Showing 1–50 of 94 results for author: Sheppard, S

Rotation and Mutual Eclipse Events Season in the Kuiper Belt: (524366) 2001 XR$_{254}$

Authors: Audrey Thirouin, William M. Grundy, Scott S. Sheppard, Keith S. Noll, José María Gómez-Limón, Benjamin Proudfoot

Abstract: (524366) 2001 XR$_{254}$ is a dynamically Cold Classical Kuiper Belt Object that is a nearly equal-sized wide binary whose upcoming mutual events season makes it a particularly valuable target for physical characterization. In advance of the mutual eclipse events, we conducted a ground-based photometric observing campaign between 2021 and 2026 using the \textit{Lowell Discovery Telescope} to inves… ▽ More (524366) 2001 XR$_{254}$ is a dynamically Cold Classical Kuiper Belt Object that is a nearly equal-sized wide binary whose upcoming mutual events season makes it a particularly valuable target for physical characterization. In advance of the mutual eclipse events, we conducted a ground-based photometric observing campaign between 2021 and 2026 using the \textit{Lowell Discovery Telescope} to investigate the rotational and physical properties of the system, to refine predictions for its future mutual events, as well as provide a lightcurve we can use as a baseline to identify eclipse events superimposed with the rotation. We derive a double-peaked asymmetric rotational lightcurve with a period of 11.17$\pm$0.04 h and a lightcurve amplitude of 0.42$\pm$0.04 mag. The lightcurve presents a sharp V-shaped minimum consistent with the primary being a close/contact binary, possibly making this a triple system. Using the Keplerian mutual orbit solution, we model the upcoming mutual event season expected between $\sim$2031 and $\sim$2040 and present some individual events for future campaigns. 2001 XR$_{254}$ is one of the few wide binary Kuiper belt systems with a well-determined mutual orbit and a soon observable mutual eclipse event season. Mutual event observations of this possible triple system will provide a rare opportunity to improve component sizes, shapes, densities, and surface properties, offering insights into the formation of the Kuiper Belt. △ Less

Submitted 29 July, 2026; originally announced July 2026.

Comments: AJ, In press

Photometry of Kuiper belt objects in inner and outer mean motion resonances with Neptune

Authors: Audrey Thirouin, Scott S. Sheppard

Abstract: We present a time-resolved photometric survey of Kuiper Belt Objects (KBOs) trapped in the inner and outer Neptune resonances. Lightcurves and rotational properties provide constraints on the shapes, internal structures, collisional histories, and formation environments of these primitive bodies. Our survey was conducted using the Magellan-Baade telescope and the Lowell Discovery Telescope, allowi… ▽ More We present a time-resolved photometric survey of Kuiper Belt Objects (KBOs) trapped in the inner and outer Neptune resonances. Lightcurves and rotational properties provide constraints on the shapes, internal structures, collisional histories, and formation environments of these primitive bodies. Our survey was conducted using the Magellan-Baade telescope and the Lowell Discovery Telescope, allowing us to go fainter than past works and yielding lightcurve studies for 41 KBOs in the 1:1, 5:4, 4:3, 11:5, 7:3, 12:5, and 5:2 resonances. We obtained complete lightcurves for objects displaying large amplitudes, with two KBOs in the 5:2 resonance (2001 XQ$_{254}$, 2013 RZ$_{108}$), one object in the 7:3 (2013 TJ$_{159}$), and one object in the 12:5 (2015 AR$_{293}$). Their lightcurve amplitudes range from 0.26 to 0.46mag, with rotational periods between 5.35 and 11.63 h. 2013 TJ$_{159}$ has the fastest rotation, largest amplitude, and most asymmetric lightcurve in our sample. Combining our results with published studies, we find that inner and outer resonant KBOs generally display lower lightcurve amplitudes than the dynamically Cold Classical population and the 5:3 and 7:4 resonances. The absence of the amplitude--period trends observed in those populations, and their surface color distributions, further suggests that inner and outer resonances do not share the same origin or evolutionary history as the Cold Classicals and overlapping resonances. Based on the literature and our survey, only one nearly equal-sized contact binary, 2004 TT$_{357}$, is currently known among the surveyed populations, implying a lower limit to the contact binary fraction of $\sim$12-15% in the 5:2 resonance. △ Less

Submitted 4 July, 2026; originally announced July 2026.

Comments: AJ, In press

You Only Stack Once (YOSO): A Motion-Filtered, Deep-Learning Framework for Detecting Faint Moving Sources

Authors: Nitya Pandey, César Fuentes, Pedro Bernardinelli, Valeria Frías, Colin Orion Chandler, David E. Trilling, Matthew J. Holman, Steven Stetzler, Dallin Spencer, Hsing Wen Lin, Luis E. Salazar Manzano, Darin Ragozzine, Ryder Strauss, Mario Jurić, Andrew J. Connolly, Hayden Smotherman, Scott S. Sheppard, Kevin Napier

Abstract: We present You Only Stack Once (YOSO), an automated pipeline designed to detect faint, slow-moving Solar System objects in wide-field astronomical surveys. The pipeline integrates a novel Gaussian Motion Filter (GMoF) that operates at the pixel level to enhance signal-to-noise for objects exhibiting a range of apparent rates of motion. Unlike conventional shift-and-stack methods, which rely on dis… ▽ More We present You Only Stack Once (YOSO), an automated pipeline designed to detect faint, slow-moving Solar System objects in wide-field astronomical surveys. The pipeline integrates a novel Gaussian Motion Filter (GMoF) that operates at the pixel level to enhance signal-to-noise for objects exhibiting a range of apparent rates of motion. Unlike conventional shift-and-stack methods, which rely on discrete velocity trials, GMoF amplifies trails while suppressing random noise and static background features. Applied to a subset of DEEP observations from the Dark Energy Camera, YOSO recovered 45 out of 73 previously detected objects, as well as 11 new TNOs. It also discovered 216 objects in the near Solar System. Although alternative shift-and-stack methods are sensitive to objects about 0.88 magnitudes fainter, YOSO's false positive rate is extremely low, since it detects only sources that exhibit a trail and are consistent with a point source when shifted at the right rate. We show how this method can be deployed on large surveys like LSST, and adapted for other domains that require motion-based signal enhancement, including exoplanet imaging through Angular Differential Imaging (ADI), and near-Earth object (NEO) detection for missions like NEO Surveyor. YOSO thus provides a versatile, scalable approach for extracting faint, motion-dependent signals in the era of data-intensive astronomy. △ Less

Submitted 7 May, 2026; originally announced May 2026.

Comments: Accepted to The Astronomical Journal; 13 pages, 9 figures

Characterization of the Volatile Properties of 133P/Elst-Pizarro and Other Main-Belt Comets with JWST and Ground-Based Observations

Authors: Henry H. Hsieh, John W. Noonan, Michael S. P. Kelley, Dennis Bodewits, Jana Pittichova, Audrey Thirouin, Marco Micheli, Scott S. Sheppard, Colin O. Chandler, Theodore Kareta, Colin Snodgrass, Richard E. Cannon, Brian P. Murphy

Abstract: We report results from an analysis of the volatile composition and evolution of main-belt comet (MBC) 133P/Elst-Pizarro using JWST NIRSpec and NIRCam observations and ground-based observations during its 2024 active apparition, and also assess the body of JWST MBC observations acquired to date. Using NIRSpec, we measure water vapor outgassing rates at two points in 133P's orbit, finding Q(H2O)=(1.… ▽ More We report results from an analysis of the volatile composition and evolution of main-belt comet (MBC) 133P/Elst-Pizarro using JWST NIRSpec and NIRCam observations and ground-based observations during its 2024 active apparition, and also assess the body of JWST MBC observations acquired to date. Using NIRSpec, we measure water vapor outgassing rates at two points in 133P's orbit, finding Q(H2O)=(1.9+/-0.6)x10^25 molecules/s on UT 2024 June 12 (at a true anomaly of nu=8 deg and heliocentric distance of rh=2.674 au), and Q(H2O)=(1.4+/-0.4)x10^25 molecules/s on UT 2024 October 14 (at nu=37.4 deg and rh=2.747 au). These measurements nominally represent a decline of ~25% in Q(H2O) between the visits, although they are also consistent with no change within uncertainties. We do not detect CO, CO2, or CH3OH, placing 133P's hypervolatile depletion (Q(CO2)/Q(H_2O)<0.009) at a similar level found for previously observed MBCs. We find log(Afrho/Q(H2O)) values for the three MBCs for which water vapor outgassing has been successfully detected that are consistent within uncertainties with an average value of log(Afrho/Q(H2O))=-24.6+/-0.2. Lastly, we find no clear correlations of water production rates with nucleus size, semimajor axis, or heliocentric distance among MBCs observed by JWST so far, but would particularly encourage future JWST observations of additional MBCs interior to the 5A:2J MMR with Jupiter and at high inclinations, as well as multiple observations of MBCs during single active apparitions to further investigate areas of interest identified from the current sample of JWST-observed MBCs. △ Less

Submitted 24 April, 2026; originally announced April 2026.

Comments: 33 pages, 13 figures, accepted for publication in PSJ

Emerging Diversity Among the Main-Belt Comets: Insights from JWST and Ground-Based Observations of 457P/Lemmon-PANSTARRS

Authors: John W. Noonan, Henry H. Hsieh, Michael S. P. Kelley, Dennis Bodewits, Jana Pittichova, Audrey Thirouin, Marco Micheli, Scott S. Sheppard, Colin O. Chandler, Theodore Kareta, Colin Snodgrass, Richard E. Cannon, Brian P. Murphy

Abstract: We present JWST NIRSpec and NIRCam observations of 457P/Lemmon-PANSTARRS, a main-belt comet that displayed activity around its 2020 perihelion and that was observed to regain activity during its 2024 perihelion by a ground-based observing campaign. The previous successful measurements of water production from two main-belt comets by the JWST NIRSpec instrument confirmed the hypothesis that H2O res… ▽ More We present JWST NIRSpec and NIRCam observations of 457P/Lemmon-PANSTARRS, a main-belt comet that displayed activity around its 2020 perihelion and that was observed to regain activity during its 2024 perihelion by a ground-based observing campaign. The previous successful measurements of water production from two main-belt comets by the JWST NIRSpec instrument confirmed the hypothesis that H2O reservoirs are responsible for activity in dynamically stable main-belt comets. However, the main-belt comets observed with JWST thus far, 238P/Read and 358P/PANSTARRS, occupy orbits in the outer main-belt, with main-belt comets with smaller semi-major axes not yet sensitively tested for H2O. We find that despite clearly displaying dust activity in both ground-based and JWST imaging over a broad period, there were no corresponding H2O, CO, CO2, or CH3OH emissions within sensitive upper limits; notable given 457P is the first main-belt comet with a semi-major axis within the 5:2 mean-motion resonance with Jupiter. We show that we were sensitive to production rates of gas predicted by the dust/gas ratios of 238P and 358P, and hypothesize that 457P may be more depleted than its companions; Q(H2O) must be less than 2x10^24 molecules/s, or 0.035 kg/s. Further surveying of main-belt comets across the parameter space of semi-major axis and eccentricity will shed light on whether 457P represents an edge member of a spectrum or a distinct subclass of main-belt comets. △ Less

Submitted 24 April, 2026; originally announced April 2026.

Comments: 27 pages, 13 figures, accepted for publication in PSJ

An Efficient Shift-and-Stack Algorithm Applied to Detection Catalogs

Authors: Steven Stetzler, Mario Jurić, Pedro H. Bernardinelli, Dino Bektešević, Colin Orion Chandler, Andrew J. Connolly, Fred C. Adams, Cesar Fuentes, David W. Gerdes, Matthew J. Holman, Hsing Wen Lin, Larissa Markwardt, Andrew McNeill, Michael Mommert, Kevin J. Napier, William J. Oldroyd, Matthew J. Payne, Andrew S. Rivkin, Luis E. Salazar-Manzano, Hilke Schlichting, Scott S. Sheppard, Dallin Spencer, Ryder Strauss, David E. Trilling, Chadwick A. Trujillo

Abstract: The boundary of solar system object discovery lies in detecting its faintest members. However, their discovery in detection catalogs from imaging surveys is fundamentally limited by the practice of thresholding detections at signal-to-noise (SNR) $\geq 5$ to maintain catalog purity. Faint moving objects can be recovered from survey images using the shift-and-stack algorithm, which coadds pixels fr… ▽ More The boundary of solar system object discovery lies in detecting its faintest members. However, their discovery in detection catalogs from imaging surveys is fundamentally limited by the practice of thresholding detections at signal-to-noise (SNR) $\geq 5$ to maintain catalog purity. Faint moving objects can be recovered from survey images using the shift-and-stack algorithm, which coadds pixels from multi-epoch images along a candidate trajectory. Trajectories matching real objects accumulate signal coherently, enabling high-confidence detections of very faint moving objects. Applying shift-and-stack comes with high computational cost, which scales with target object velocity, typically limiting its use to searches for slow-moving objects in the outer solar system. This work introduces a modified shift-and-stack algorithm that trades sensitivity for speedup. Our algorithm stacks low SNR detection catalogs instead of pixels, the sparsity of which enables approximations that reduce the number of stacks required. Our algorithm achieves real-world speedups of $10$--$10^3 \times$ over image-based shift-and-stack while retaining the ability to find faint objects. We validate its performance by recovering synthetic inner and outer solar system objects injected into images from the DECam Ecliptic Exploration Project (DEEP). Exploring the sensitivity--compute time trade-off of this algorithm, we find that our method achieves a speedup of $\sim30\times$ with $88\%$ of the memory usage while sacrificing $0.25$ mag in depth compared to image-based shift-and-stack. These speedups enable the broad application of shift-and-stack to large-scale imaging surveys and searches for faint inner solar system objects. We provide a reference implementation via the find-asteroids Python package and this URL: https://github.com/stevenstetzler/find-asteroids. △ Less

Submitted 30 September, 2025; originally announced September 2025.

Comments: 35 pages, 15 figures, accepted for publication in The Astronomical Journal

Evaluating an Embryo Origin for Detached TNOs within Full Kuiper Belt Formation Models

Authors: Nathan A. Kaib, Chadwick A. Trujillo, Scott S. Sheppard

Abstract: With perihelia well beyond Neptune, but semimajor axes and eccentricities indicative of substantial perturbation, the origins of detached trans-Neptunian objects (TNOs) remain a dynamical puzzle. In particular, detached TNOs with orbital inclinations below ~25 degrees are not easily generated from any known mechanism currently in the modern solar system. One notable hypothesis for the origins of d… ▽ More With perihelia well beyond Neptune, but semimajor axes and eccentricities indicative of substantial perturbation, the origins of detached trans-Neptunian objects (TNOs) remain a dynamical puzzle. In particular, detached TNOs with orbital inclinations below ~25 degrees are not easily generated from any known mechanism currently in the modern solar system. One notable hypothesis for the origins of detached TNOs is that a ~Mars- to Earth-mass planetary embryo detached the perihelia of these objects from Neptune during the process of Kuiper belt formation before the embryo itself was ejected. We numerically model this scenario via simulations of Kuiper belt formation from a primordial planetesimal belt that is dispersed through the migration of the giant planets. In addition to ~100,000 Kuiper belt objects, each of our simulations contains a hypothetical population of embryos in the primordial belt. We find that our embryos are unlikely to reach the high-perihelion, large semimajor axis orbit necessary to efficiently detach TNO perihelia from Neptune's influence. Moreover, embryos will typically take at least 100 Myrs to reach these unlikely orbits, at which point most of the primordial belt will have already been ejected by the planets, limiting the available population that can be detached. Finally, the TNOs that our embryos do detach consistently have a semimajor axis distribution that is more biased toward small values than observed detached TNOs have. Thus, we conclude that planetary embryos in the primordial Kuiper belt are not likely to have been the primary mechanism for the origin of detached TNOs. △ Less

Submitted 4 July, 2025; originally announced July 2025.

Comments: 12 pages, 8 figures, Accepted for publication in Icarus

Colors and Dynamics of a Near-Sun Orbital Asteroid Family: 2021 PH27 and 2025 GN1

Authors: Scott Sheppard, Henry Hsieh, Petr Pokorny, David Tholen, Audrey Thirouin, Carlos Contreras, Marcelo Mora, Mauricio Martinez, Ivonne Toro

Abstract: We observed the dynamically similar near-Sun asteroids 2021 PH27 and 2025 GN1 for their optical colors. These objects have the lowest known semi-major axes of any asteroids. 2021 PH27 has the largest general relativistic effects of any known solar system object. The small semi-major axis and very close passage to the Sun suggests the extreme thermal and gravitational environment should highly modi… ▽ More We observed the dynamically similar near-Sun asteroids 2021 PH27 and 2025 GN1 for their optical colors. These objects have the lowest known semi-major axes of any asteroids. 2021 PH27 has the largest general relativistic effects of any known solar system object. The small semi-major axis and very close passage to the Sun suggests the extreme thermal and gravitational environment should highly modify these asteroids' surfaces. From g', r', i' and z'-band imaging, we find the colors of 2021 PH27 to be between the two major asteroid types the S and C classes (g'-r'= 0.58 +- 0.02, r'-i'=0.12 +- 0.02 and i'-z'=-0.08 +- 0.05 mags). With a spectral slope of 6.8 +-0.03 percent per 100nm, 2021 PH27 is a X-type asteroid and requires albedo or spectral features to further identify its composition. We find the dynamically similar 2025 GN1 also has very similar colors (g'-r'=0.55 +-0.06 and r'-i'=0.14 +-0.04) as 2021 PH27, suggesting these objects are fragments from a once larger parent asteroid or 2021 PH27 is shedding material. The colors are not blue like some other near-Sun asteroids such as 3200 Phaethon that have been interpreted to be from the loss of reddening substances from the extreme temperatures. There is no evidence of activity or a large amplitude period for 2021 PH27, whereas 2025 GN1 might have a more significant rotational light curve. 2025 GN1 may have a very close encounter or hit Venus in about 2155 years and likely separated from 2021 PH27 in about the last 10 kyrs. △ Less

Submitted 22 April, 2025; originally announced April 2025.

Comments: Submitted

Logos-Zoe: A contact binary triple system in the trans-neptunian belt

Authors: Audrey Thirouin, Keith S. Noll, William M. Grundy, Scott S. Sheppard, Felicity Escarzaga, Brian Donnelly

Abstract: The trans-neptunian object (58534) 1997 CQ$_{29}$ (a.k.a. Logos) is a resolved wide binary in the dynamically Cold Classical population. With Hubble Space Telescope resolved observations where the primary Logos is well separated from its secondary Zoe it can be established that Logos has a time-variable brightness. Logos' brightness varied by several tenths of a magnitude over a short timescale of… ▽ More The trans-neptunian object (58534) 1997 CQ$_{29}$ (a.k.a. Logos) is a resolved wide binary in the dynamically Cold Classical population. With Hubble Space Telescope resolved observations where the primary Logos is well separated from its secondary Zoe it can be established that Logos has a time-variable brightness. Logos' brightness varied by several tenths of a magnitude over a short timescale of hours while the brightness variability of Zoe was on a longer timescale. New unresolved ground-based observations obtained with the Lowell Discovery Telescope and the Magellan-Baade telescope confirm at least one highly variable component in this system. With our ground-based observations and photometric constraints from space-based observations, we suggest that the primary Logos is likely a close/contact binary whose rotational period is 17.43$\pm$0.06 h for a lightcurve amplitude of 0.70$\pm$0.07 mag while Zoe is potentially a (very) slow rotator with an unknown shape. Using the Candela software, we model the Logos-Zoe system and predict its upcoming mutual events season using rotational, physical, and mutual orbit parameters derived in this work or already published. Zoe's shape and rotational period are still uncertain, so we consider various options to better understand Zoe. The upcoming mutual event season for Logos-Zoe starts in 2026 and will last for four years with up to two events per year. Observations of these mutual events will allow us to significantly improve the physical and rotational properties of both Logos and Zoe. △ Less

Submitted 21 April, 2025; originally announced April 2025.

Comments: Accepted for publication

The Volatile Composition and Activity Evolution of Main-Belt Comet 358P/PANSTARRS

Authors: Henry H. Hsieh, John W. Noonan, Michael S. P. Kelley, Dennis Bodewits, Jana Pittichova, Audrey Thirouin, Marco Micheli, Matthew M. Knight, Michele T. Bannister, Colin O. Chandler, Carrie E. Holt, Matthew J. Hopkins, Yaeji Kim, Nicholas A. Moskovitz, William J. Oldroyd, Jack Patterson, Scott S. Sheppard, Nicole Tan, Chadwick A. Trujillo, Quanzhi Ye

Abstract: We report the detection of water vapor associated with main-belt comet 358P/PANSTARRS on UT 2024 January 8-9 using the NIRSPEC instrument aboard JWST. We derive a water production rate of Q(H2O)=(5.0+/-0.2)x10^25 molecules/s, marking only the second direct detection of sublimation products of any kind from a main-belt comet, after 238P/Read. Similar to 238P, we find a remarkable absence of hypervo… ▽ More We report the detection of water vapor associated with main-belt comet 358P/PANSTARRS on UT 2024 January 8-9 using the NIRSPEC instrument aboard JWST. We derive a water production rate of Q(H2O)=(5.0+/-0.2)x10^25 molecules/s, marking only the second direct detection of sublimation products of any kind from a main-belt comet, after 238P/Read. Similar to 238P, we find a remarkable absence of hypervolatile species, finding Q(CO2)<7.6x10^22 molecules/s, corresponding to Q(CO2)/Q(H2O)<0.2%. Upper limits on CH3OH and CO emission are also estimated. Photometry from ground-based observations show that the dust coma brightened and faded slowly over ~250 days in 2023-2024, consistent with photometric behavior observed in 2012-2013, but also indicate a ~2.5x decline in the dust production rate between these two periods. Dynamical dust modeling shows that the coma's morphology as imaged by JWST's NIRCAM instrument on 2023 November 22 can be reproduced by asymmetric dust emission from a nucleus with a mid-range obliquity (~80 deg) with a steady-state mass loss rate of ~0.8 kg/s. Finally, we find similar Afrho-to-gas ratios of log10(Afrho/Q(H2O))=-24.8+/-0.2 for 358P and log10(Afrho/QH2O)=-24.4+/-0.2 for 238P, suggesting that Afrho could serve as an effective proxy for estimating water production rates in other active main-belt comets. The confirmation of water vapor outgassing in both main-belt comets observed by JWST to date reinforces the use of recurrent activity near perihelion as an indicator of sublimation-driven activity in active asteroids. △ Less

Submitted 11 November, 2024; originally announced November 2024.

Comments: 32 pages, 13 figures. Accepted for publication in The Planetary Science Journal

The DECam Ecliptic Exploration Project (DEEP). VII. The Strengths of Three Superfast Rotating Main-belt Asteroids from a Preliminary Search of DEEP Data

Authors: Ryder Strauss, Andrew McNeill, David E. Trilling, Francisco Valdes, Pedro H. Bernardinell, Cesar Fuentes, David W. Gerdes, Matthew J. Holman, Mario Juric, Hsing Wen Lin, Larissa Markwardt, Michael Mommert, Kevin J. Napier, William J. Oldroyd, Matthew J. Payne, Andrew S. Rivkin, Hilke E. Schlichting, Scott S. Sheppard, Hayden Smotherman, Chadwick A Trujillo, Fred C. Adams, Colin Orion Chandler

Abstract: Superfast rotators (SFRs) are small solar system objects that rotate faster than generally possible for a cohesionless rubble pile. Their rotational characteristics allow us to make inferences about their interior structure and composition. Here, we present the methods and results from a preliminary search for SFRs in the DECam Ecliptic Exploration Project (DEEP) data set. We find three SFRs from… ▽ More Superfast rotators (SFRs) are small solar system objects that rotate faster than generally possible for a cohesionless rubble pile. Their rotational characteristics allow us to make inferences about their interior structure and composition. Here, we present the methods and results from a preliminary search for SFRs in the DECam Ecliptic Exploration Project (DEEP) data set. We find three SFRs from a sample of 686 main-belt asteroids, implying an occurrence rate of 0.4 -0.3/+0.1 percent - a higher incidence rate than has been measured by previous studies. We suggest that this high occurrence rate is due to the small sub-kilometer size regime to which DEEP has access: the objects searched here were as small as 500 m. We compute the minimum required cohesive strength for each of these SFRs and discuss the implications of these strengths in the context of likely evolution mechanisms. We find that all three of these SFRs require strengths that are more than that of weak regolith but consistent with many cohesive asteroid strengths reported in the literature. Across the full DEEP data set, we have identified ~70,000 Main-Belt Asteroids and expect ~300 SFRs - a result that will be assessed in a future paper. △ Less

Submitted 1 October, 2024; originally announced October 2024.

Journal ref: The Astronomical Journal, Volume 168, Number 4 (2024)

New Moons of Uranus and Neptune from Ultra-Deep Pencil Beam Surveys

Authors: Scott Sheppard, David Tholen, Marina Brozovic, Robert Jacobson, Chadwick Trujillo, Patryk Sofia Lykawka, Mike Alexandersen

Abstract: We have conducted extremely ultra-deep pencil beam observations for new satellites around both Uranus and Neptune. Tens of images on several different nights in 2021, 2022 and 2023 were obtained and shifted and added together to reach as faint as 26.9 and 27.2 magnitudes in the r-band around Uranus and Neptune, respectively. One new moon of Uranus, S/2023 U1, and two new moons of Neptune, S/2021 N… ▽ More We have conducted extremely ultra-deep pencil beam observations for new satellites around both Uranus and Neptune. Tens of images on several different nights in 2021, 2022 and 2023 were obtained and shifted and added together to reach as faint as 26.9 and 27.2 magnitudes in the r-band around Uranus and Neptune, respectively. One new moon of Uranus, S/2023 U1, and two new moons of Neptune, S/2021 N1 and S/2002 N5, were found. S/2023 U1 was 26.6 mags, is about 7 km in diameter and has a distant, eccentric and inclined retrograde orbit similar to Caliban and Stephano, implying these satellites are fragments from a once larger parent satellite. S/2023 U1 almost completely overlaps Stephano in orbital phase space. S/2021 N1 was 26.9 mags, about 14 km in size and has a retrograde orbit similar to Neso and Psamathe, indicating they are a dynamical family. We find S/2021 N1 is in a Kozai-Lidov orbital resonance. S/2002 N5 was 25.9 mags, is about 23 km in size and it makes a family of distant prograde satellites with Sao and Laomedeia. All three new moons show for the first time dynamical groups of moons exist around both Uranus and Neptune. The creation of these groups likely produced dust that could be the source of red material seen on the leading hemispheres of some larger inner satellites like Titania, Oberon and Umbriel. We also detected all known outer moons of Uranus and Neptune on multiple nights. This survey mostly completes the outer satellites of Uranus to about 8 km and Neptune to about 14 km in diameter. The size distributions of satellite dynamical families around the giant planets shows a strong steepening in the power law size distribution smaller than 5 km in diameter. The satellites of a family become much more common smaller than 5 km and their size distribution is consistent with a collisional break-up of a once larger parent satellite. △ Less

Submitted 30 September, 2024; originally announced October 2024.

Comments: Accepted Astronomical Journal

Correcting for objective sample refractive index mismatch in extended field of view selective plane illumination microscopy

Authors: Steven J. Sheppard, Peter T. Brown, Douglas P. Shepherd

Abstract: Selective plane illumination microscopy (SPIM) is an optical sectioning imaging approach based on orthogonal light pathways for excitation and detection. The excitation pathway has an inverse relation between the optical sectioning strength and the effective field of view (FOV). Multiple approaches exist to extend the effective FOV, and here we focus on remote focusing to axially scan the light sh… ▽ More Selective plane illumination microscopy (SPIM) is an optical sectioning imaging approach based on orthogonal light pathways for excitation and detection. The excitation pathway has an inverse relation between the optical sectioning strength and the effective field of view (FOV). Multiple approaches exist to extend the effective FOV, and here we focus on remote focusing to axially scan the light sheet, synchronized with a CMOS camera's rolling shutter. A typical axially scanned SPIM configuration for imaging large samples utilizes a tunable optic for remote focusing, paired with air objectives focused into higher refractive index media. To quantitatively explore the effect of remote focus choices and sample space refractive index mismatch on light sheet intensity distributions, we developed a computational model integrating ray tracing and field propagation. We validate our model's performance against experimental light sheet profiles for various SPIM configurations. Our findings indicate that optimizing the position of the sample chamber relative to the excitation optics can enhance image quality by balancing aberrations induced by refractive index mismatch. We validate this prediction using a homebuilt, large sample axially scanned SPIM configuration and calibration samples. △ Less

Submitted 26 July, 2024; originally announced July 2024.

The Active Asteroids Citizen Science Program: Overview and First Results

Authors: Colin Orion Chandler, Chadwick A. Trujillo, William J. Oldroyd, Jay K. Kueny, William A. Burris, Henry H. Hsieh, Jarod A. DeSpain, Nima Sedaghat, Scott S. Sheppard, Kennedy A. Farrell, David E. Trilling, Annika Gustafsson, Mark Jesus Mendoza Magbanua, Michele T. Mazzucato, Milton K. D. Bosch, Tiffany Shaw-Diaz, Virgilio Gonano, Al Lamperti, José A. da Silva Campos, Brian L. Goodwin, Ivan A. Terentev, Charles J. A. Dukes, Sam Deen

Abstract: We present the Citizen Science program Active Asteroids and describe discoveries stemming from our ongoing project. Our NASA Partner program is hosted on the Zooniverse online platform and launched on 2021 August 31, with the goal of engaging the community in the search for active asteroids -- asteroids with comet-like tails or comae. We also set out to identify other unusual active solar system o… ▽ More We present the Citizen Science program Active Asteroids and describe discoveries stemming from our ongoing project. Our NASA Partner program is hosted on the Zooniverse online platform and launched on 2021 August 31, with the goal of engaging the community in the search for active asteroids -- asteroids with comet-like tails or comae. We also set out to identify other unusual active solar system objects, such as active Centaurs, active quasi-Hilda asteroids, and Jupiter-family comets (JFCs). Active objects are rare in large part because they are difficult to identify, so we ask volunteers to assist us in searching for active bodies in our collection of millions of images of known minor planets. We produced these cutout images with our project pipeline that makes use of publicly available Dark Energy Camera (DECam) data. Since the project launch, roughly 8,300 volunteers have scrutinized some 430,000 images to great effect, which we describe in this work. In total we have identified previously unknown activity on 15 asteroids, plus one Centaur, that were thought to be asteroidal (i.e., inactive). Of the asteroids, we classify four as active quasi-Hilda asteroids, seven as JFCs, and four as active asteroids, consisting of one Main-belt comet (MBC) and three MBC candidates. We also include our findings concerning known active objects that our program facilitated, an unanticipated avenue of scientific discovery. These include discovering activity occurring during an orbital epoch for which objects were not known to be active, and the reclassification of objects based on our dynamical analyses. △ Less

Submitted 14 March, 2024; originally announced March 2024.

Comments: 35 pages, 5 figures, 3 tables

The New Horizons Extended Mission Target: Arrokoth Search and Discovery

Authors: Marc W. Buie, John R. Spencer, Simon B. Porter, Susan D. Benecchi, Alex H. Parker, S. Alan Stern, Michael Belton, Richard P. Binzel, David Borncamp, Francesca DeMeo, S. Fabbro, Cesar Fuentes, Hisanori Furusawa, Tetsuharu Fuse, Pamela L. Gay, Stephen Gwyn, Matthew J. Holman, H. Karoji, J. J. Kavelaars, Daisuke Kinoshita, Satoshi Miyazaki, Matt Mountain, Keith S. Noll, David J. Osip, Jean-Marc Petit , et al. (15 additional authors not shown)

Abstract: Following the Pluto fly-by of the New Horizons spacecraft, the mission provided a unique opportunity to explore the Kuiper Belt in-situ. The possibility existed to fly-by a Kuiper Belt object (KBO) as well as to observe additional objects at distances closer than are feasible from earth-orbit facilities. However, at the time of launch no KBOs were known about that were accessible by the spacecraft… ▽ More Following the Pluto fly-by of the New Horizons spacecraft, the mission provided a unique opportunity to explore the Kuiper Belt in-situ. The possibility existed to fly-by a Kuiper Belt object (KBO) as well as to observe additional objects at distances closer than are feasible from earth-orbit facilities. However, at the time of launch no KBOs were known about that were accessible by the spacecraft. In this paper we present the results of 10 years of observations and three uniquely dedicated efforts -- two ground-based using the Subaru Suprime Camera, the Magellan MegaCam and IMACS Cameras, and one with the Hubble Space Telescope -- to find such KBOs for study. In this paper we overview the search criteria and strategies employed in our work and detail the analysis efforts to locate and track faint objects in the galactic plane. We also present a summary of all of the KBOs that were discovered as part of our efforts and how spacecraft targetability was assessed, including a detailed description of our astrometric analysis which included development of an extensive secondary calibration network. Overall, these efforts resulted in the discovery of 89 KBOs including 11 which became objects for distant observation by New Horizons and (486958) Arrokoth which became the first post-Pluto fly-by destination. △ Less

Submitted 3 July, 2024; v1 submitted 7 March, 2024; originally announced March 2024.

Comments: Accepted to PSJ. 40 pages, 10 figures, 10 tables

Rotational Study of 5:3 and 7:4 Resonant Objects within the Main Classical Trans-Neptunian Belt

Authors: Audrey Thirouin, Scott S. Sheppard

Abstract: The 5:3 and 7:4 mean motion resonances of Neptune are at 42.3 and 43.7 au, respectively, and overlap with objects in the Classical trans-neptunian belt (Kuiper belt). We report the complete/partial lightcurves of 13 and 14 trans-Neptunian objects (TNOs) in the 5:3 and 7:4 resonances, respectively. We report a most likely contact binary in the 7:4 resonance, 2013 FR$_{28}$, with a periodicity of 13… ▽ More The 5:3 and 7:4 mean motion resonances of Neptune are at 42.3 and 43.7 au, respectively, and overlap with objects in the Classical trans-neptunian belt (Kuiper belt). We report the complete/partial lightcurves of 13 and 14 trans-Neptunian objects (TNOs) in the 5:3 and 7:4 resonances, respectively. We report a most likely contact binary in the 7:4 resonance, 2013 FR$_{28}$, with a periodicity of 13.97$\pm$0.04 h and a lightcurve amplitude of 0.94$\pm$0.02 mag. With a V-/U-shaped lightcurve, 2013 FR$_{28}$ has one of the largest well-sampled TNO amplitude observed with ground-based observations, comparable to the well-determined contact binary 2001 QG$_{298}$. 2013 FR$_{28}$ has a mass ratio q$\sim$1 with a density $ρ$$\sim$1 g cm$^{-3}$. We find several objects with large amplitudes and classify 2004 SC$_{60}$, 2006 CJ$_{69}$, and 2013 BN$_{82}$ as likely contact binaries, and 2001 QF$_{331}$, 2003 YW$_{179}$, and 2015 FP$_{345}$ as likely elongated objects. We observe the 17:9 resonant or classical object 2003 SP$_{317}$ that we classify as a likely contact binary. A lower estimate of 10-50% and 20-55% for the fraction of (nearly) equal-sized contact binaries is calculated in the 5:3 and 7:4 resonances, respectively. Surface colors of 2004 SC$_{60}$, 2013 BN$_{82}$, 2014 OL$_{394}$, and 2015 FP$_{345}$ have been obtained. Including these colors with ones from the literature reveals that elongated objects and contact binaries share the same ultra-red surface color, except Manwë-Thorondor and 2004 SC$_{60}$. Not only are the colors of the 7:4 and 5:3 TNOs similar to the Cold Classicals, but we demonstrate that the rotational properties of the 5:3 and 7:4 resonants are similar to those of the Cold Classicals, inferring a clear link between these sub-populations. △ Less

Submitted 7 February, 2024; originally announced February 2024.

Comments: Accepted for publication in Planetary Science Journal (PSJ)

WindCline: Sloping Wind Tunnel for Characterizing Flame Behavior Under Variable Inclines and Wind Conditions

Authors: Amanda S. Makowiecki, Sean C. Coburn, Samantha Sheppard, Brendan Bitterlin, Timothy Breda, Abdul Dawlatzai, Robert Giannella, Alexandra Jaros, Christopher Kling, Eric Kolb, Caelan Lapointe, Sam Simons-Wellin, Hope A. Michelsen, John W. Daily, Michael Hannigan, Peter E. Hamlington, John Farnsworth, Gregory B. Rieker

Abstract: Developing accurate computational models of wildfire dynamics is increasingly important due to the substantial and expanding negative impacts of wildfire events on human health, infrastructure, and the environment. Wildfire spread and emissions depend on a number of factors, including fuel type, environmental conditions (moisture, wind speed, etc.) and terrain/location. However, there currently ex… ▽ More Developing accurate computational models of wildfire dynamics is increasingly important due to the substantial and expanding negative impacts of wildfire events on human health, infrastructure, and the environment. Wildfire spread and emissions depend on a number of factors, including fuel type, environmental conditions (moisture, wind speed, etc.) and terrain/location. However, there currently exist only a few experimental facilities that enable testing of the interplay of these factors at length scales <1 m with carefully controlled and characterized boundary conditions and advanced diagnostics. Experiments performed at such facilities are required for informing and validating computational models. Here we present the design and characterization of a novel tilting wind tunnel (the 'WindCline') for studying wildfire dynamics. The WindCline is unique in that the entire tunnel platform is constructed to pivot around a central axis, which enables sloping of the entire system without compromising the quality of the flow properties. In addition, this facility has a configurable design for the test section and diffuser to accommodate a suite of advanced diagnostics to aid in the characterization of 1) the parameters needed to establish boundary conditions and 2) flame properties and dynamics. The WindCline thus allows for measurement and control of several critical wildfire variables and boundary conditions, especially at the small length scales important to the development of high fidelity computational simulations (10 - 100 cm). Computational modeling frameworks developed and validated under these controlled conditions can expand understanding of fundamental combustion processes, promoting greater confidence when leveraging these processes in complex combustion environments. △ Less

Submitted 3 December, 2023; originally announced December 2023.

Comments: 27 pages, 12 figures + 6 in supplemental material, submitted to Review of Scientific Instruments

Recurring Activity Discovered on Quasi-Hilda 2009 DQ118

Authors: William J. Oldroyd, Colin Orion Chandler, Chadwick A. Trujillo, Scott S. Sheppard, Henry H. Hsieh, Jay K. Kueny, William A. Burris, Jarod A. DeSpain, Kennedy A. Farrell, Michele T. Mazzucato, Milton K. D. Bosch, Tiffany Shaw-Diaz, Virgilio Gonano

Abstract: We have discovered two epochs of activity on quasi-Hilda 2009 DQ118. Small bodies that display comet-like activity, such as active asteroids and active quasi-Hildas, are important for understanding the distribution of water and other volatiles throughout the solar system. Through our NASA Partner Citizen Science project, Active Asteroids, volunteers classified archival images of 2009 DQ118 as disp… ▽ More We have discovered two epochs of activity on quasi-Hilda 2009 DQ118. Small bodies that display comet-like activity, such as active asteroids and active quasi-Hildas, are important for understanding the distribution of water and other volatiles throughout the solar system. Through our NASA Partner Citizen Science project, Active Asteroids, volunteers classified archival images of 2009 DQ118 as displaying comet-like activity. By performing an in-depth archival image search, we found over 20 images from UT 2016 March 8--9 with clear signs of a comet-like tail. We then carried out follow-up observations of 2009 DQ118 using the 3.5 m Astrophysical Research Consortium Telescope at Apache Point Observatory, Sunspot, New Mexico, USA and the 6.5 m Magellan Baade Telescope at Las Campanas Observatory, Chile. These images revealed a second epoch of activity associated with the UT 2023 April 22 perihelion passage of 2009 DQ118. We performed photometric analysis of the tail and find that it had a similar apparent length and surface brightness during both epochs. We also explored the orbital history and future of 2009 DQ118 through dynamical simulations. These simulations show that 2009 DQ118 is currently a quasi-Hilda and that it frequently experiences close encounters with Jupiter. We find that 2009 DQ118 is currently on the boundary between asteroidal and cometary orbits. Additionally, it has likely been a Jupiter family comet or Centaur for much of the past 10 kyr and will be in these same regions for the majority of the next 10 kyr. Since both detected epochs of activity occurred near perihelion, the observed activity is consistent with sublimation of volatile ices. 2009 DQ118 is currently observable until ~mid-October 2023. Further observations would help to characterize the observed activity. △ Less

Submitted 3 November, 2023; originally announced November 2023.

Comments: 10 pages, 3 figures

Journal ref: ApJL, 957, L1 (2023)

The DECam Ecliptic Exploration Project (DEEP) II. Observational Strategy and Design

Authors: Chadwick A. Trujillo, Cesar Fuentes, David W. Gerdes, Larissa Markwardt, Scott S. Sheppard, Ryder Strauss, Colin Orion Chandler, William J. Oldroyd, David E. Trilling, Hsing Wen Lin, Fred C. Adams, Pedro H. Bernardinelli, Matthew J. Holman, Mario Juric, Andrew McNeill, Michael Mommert, Kevin J. Napier, Matthew J. Payne, Darin Ragozzine, Andrew S. Rivkin, Hilke Schlichting, Hayden Smotherman

Abstract: We present the DECam Ecliptic Exploration Project (DEEP) survey strategy including observing cadence for orbit determination, exposure times, field pointings and filter choices. The overall goal of the survey is to discover and characterize the orbits of a few thousand Trans-Neptunian Objects (TNOs) using the Dark Energy Camera (DECam) on the Cerro Tololo Inter-American Observatory (CTIO) Blanco 4… ▽ More We present the DECam Ecliptic Exploration Project (DEEP) survey strategy including observing cadence for orbit determination, exposure times, field pointings and filter choices. The overall goal of the survey is to discover and characterize the orbits of a few thousand Trans-Neptunian Objects (TNOs) using the Dark Energy Camera (DECam) on the Cerro Tololo Inter-American Observatory (CTIO) Blanco 4 meter telescope. The experiment is designed to collect a very deep series of exposures totaling a few hours on sky for each of several 2.7 square degree DECam fields-of-view to achieve a magnitude of about 26.2 using a wide VR filter which encompasses both the V and R bandpasses. In the first year, several nights were combined to achieve a sky area of about 34 square degrees. In subsequent years, the fields have been re-visited to allow TNOs to be tracked for orbit determination. When complete, DEEP will be the largest survey of the outer solar system ever undertaken in terms of newly discovered object numbers, and the most prolific at producing multi-year orbital information for the population of minor planets beyond Neptune at 30 au. △ Less

Submitted 30 October, 2023; originally announced October 2023.

Comments: 29 pages, 4 figures and 4 tables

The DECam Ecliptic Exploration Project (DEEP) VI: first multi-year observations of trans-Neptunian objects

Authors: Hayden Smotherman, Pedro H. Bernardinelli, Stephen K. N. Portillo, Andrew J. Connolly, J. Bryce Kalmbach, Steven Stetzler, Mario Juric, Dino Bektesvic, Zachary Langford, Fred C. Adams, William J. Oldroyd, Matthew J. Holman, Colin Orion Chandler, Cesar Fuentes, David W. Gerdes, Hsing Wen Lin, Larissa Markwardt, Andrew McNeill, Michael Mommert, Kevin J. Napier, Matthew J. Payne, Darin Ragozzine, Andrew S. Rivkin, Hilke Schlichting, Scott S. Sheppard , et al. (3 additional authors not shown)

Abstract: We present the first set of trans-Neptunian objects (TNOs) observed on multiple nights in data taken from the DECam Ecliptic Exploration Project (DEEP). Of these 110 TNOs, 105 do not coincide with previously known TNOs and appear to be new discoveries. Each individual detection for our objects resulted from a digital tracking search at TNO rates of motion, using two to four hour exposure sets, and… ▽ More We present the first set of trans-Neptunian objects (TNOs) observed on multiple nights in data taken from the DECam Ecliptic Exploration Project (DEEP). Of these 110 TNOs, 105 do not coincide with previously known TNOs and appear to be new discoveries. Each individual detection for our objects resulted from a digital tracking search at TNO rates of motion, using two to four hour exposure sets, and the detections were subsequently linked across multiple observing seasons. This procedure allows us to find objects with magnitudes $m_{VR} \approx 26$. The object discovery processing also included a comprehensive population of objects injected into the images, with a recovery and linking rate of at least $94\%$. The final orbits were obtained using a specialized orbit fitting procedure that accounts for the positional errors derived from the digital tracking procedure. Our results include robust orbits and magnitudes for classical TNOs with absolute magnitudes $H \sim 10$, as well as a dynamically detached object found at 76 au (semi-major axis $a\approx 77 \, \mathrm{au}$). We find a disagreement between our population of classical TNOs and the CFEPS-L7 three component model for the Kuiper belt. △ Less

Submitted 5 October, 2023; originally announced October 2023.

Comments: Accepted to AJ, companion paper do DEEP III. Objects will be released in the journal version (or contacting the authors)

The DECam Ecliptic Exploration Project (DEEP) III: Survey characterization and simulation methods

Authors: Pedro H. Bernardinelli, Hayden Smotherman, Zachary Langford, Stephen K. N. Portillo, Andrew J. Connolly, J. Bryce Kalmbach, Steven Stetzler, Mario Juric, William J. Oldroyd, Hsing Wen Lin, Fred C. Adams, Colin Orion Chandler, Cesar Fuentes, David W. Gerdes, Matthew J. Holman, Larissa Markwardt, Andrew McNeill, Michael Mommert, Kevin J. Napier, Matthew J. Payne, Darin Ragozzine, Andrew S. Rivkin, Hilke Schlichting, Scott S. Sheppard, Ryder Strauss , et al. (2 additional authors not shown)

Abstract: We present a detailed study of the observational biases of the DECam Ecliptic Exploration Project's (DEEP) B1 data release and survey simulation software that enables direct statistical comparisons between models and our data. We inject a synthetic population of objects into the images, and then subsequently recover them in the same processing as our real detections. This enables us to characteriz… ▽ More We present a detailed study of the observational biases of the DECam Ecliptic Exploration Project's (DEEP) B1 data release and survey simulation software that enables direct statistical comparisons between models and our data. We inject a synthetic population of objects into the images, and then subsequently recover them in the same processing as our real detections. This enables us to characterize the survey's completeness as a function of apparent magnitudes and on-sky rates of motion. We study the statistically optimal functional form for the magnitude, and develop a methodology that can estimate the magnitude and rate efficiencies for all survey's pointing groups simultaneously. We have determined that our peak completeness is on average 80\% in each pointing group, and our magnitude drops to $25\%$ of this value at $m_{25} = 26.22$. We describe the freely available survey simulation software and its methodology. We conclude by using it to infer that our effective search area for objects at 40 au is $14.8°^2$, and that our lack of dynamically cold distant objects means that there at most $8\times 10^3$ objects with $60 < a < 80$ au and absolute magnitudes $H \leq 8$. △ Less

Submitted 5 October, 2023; originally announced October 2023.

Comments: Accepted to AJ, companion paper to DEEP VI

The DECam Ecliptic Exploration Project (DEEP) IV: Constraints on the shape distribution of bright TNOs

Authors: R. Strauss, D. E. Trilling, P. H. Bernardinelli, C. Beach, W. J. Oldroyd, S. S. Sheppard, H. E. Schlichting, D. W. Gerdes, F. C. Adams, C. O. Chandler, C. Fuentes, M. J. Holman, M. Jurić, H. W. Lin, L. Markwardt, A. McNeill, M. Mommert, K. J. Napier, M. J. Payne, D. Ragozzine, A. S. Rivkin, H. Smotherman, C. A. Trujillo

Abstract: We present the methods and results from the discovery and photometric measurement of 26 bright (VR $>$ 24 trans-Neptunian objects (TNOs) during the first year (2019-20) of the DECam Ecliptic Exploration Project (DEEP). The DEEP survey is an observational TNO survey with wide sky coverage, high sensitivity, and a fast photometric cadence. We apply a computer vision technique known as a progressive… ▽ More We present the methods and results from the discovery and photometric measurement of 26 bright (VR $>$ 24 trans-Neptunian objects (TNOs) during the first year (2019-20) of the DECam Ecliptic Exploration Project (DEEP). The DEEP survey is an observational TNO survey with wide sky coverage, high sensitivity, and a fast photometric cadence. We apply a computer vision technique known as a progressive probabilistic Hough transform to identify linearly-moving transient sources within DEEP photometric catalogs. After subsequent visual vetting, we provide a photometric and astrometric catalog of our TNOs. By modeling the partial lightcurve amplitude distribution of the DEEP TNOs using Monte Carlo techniques, we find our data to be most consistent with an average TNO axis ratio b/a $<$ 0.5, implying a population dominated by non-spherical objects. Based on ellipsoidal gravitational stability arguments, we find our data to be consistent with a TNO population containing a high fraction of contact binaries or other extremely non-spherical objects. We also discuss our data as evidence that the expected binarity fraction of TNOs may be size-dependent. △ Less

Submitted 7 September, 2023; originally announced September 2023.

The DECam Ecliptic Exploration Project (DEEP): I. Survey description, science questions, and technical demonstration

Authors: David E. Trilling, David W. Gerdes, Mario Juric, Chadwick A. Trujillo, Pedro H. Bernardinelli, Kevin J. Napier, Hayden Smotherman, Ryder Strauss, Cesar Fuentes, Matthew J. Holman, Hsing Wen Lin, Larissa Markwardt, Andrew McNeill, Michael Mommert, William J. Oldroyd, Matthew J. Payne, Darin Ragozzine, Andrew S. Rivkin, Hilke Schlichting, Scott S. Sheppard, Fred C. Adams, Colin Orion Chandler

Abstract: We present here the DECam Ecliptic Exploration Project (DEEP), a three year NOAO/NOIRLab Survey that was allocated 46.5 nights to discover and measure the properties of thousands of trans-Neptunian objects (TNOs) to magnitudes as faint as VR~27, corresponding to sizes as small as 20 km diameter. In this paper we present the science goals of this project, the experimental design of our survey, and… ▽ More We present here the DECam Ecliptic Exploration Project (DEEP), a three year NOAO/NOIRLab Survey that was allocated 46.5 nights to discover and measure the properties of thousands of trans-Neptunian objects (TNOs) to magnitudes as faint as VR~27, corresponding to sizes as small as 20 km diameter. In this paper we present the science goals of this project, the experimental design of our survey, and a technical demonstration of our approach. The core of our project is "digital tracking," in which all collected images are combined at a range of motion vectors to detect unknown TNOs that are fainter than the single exposure depth of VR~23 mag. Through this approach we reach a depth that is approximately 2.5 magnitudes fainter than the standard LSST "wide fast deep" nominal survey depth of 24.5 mag. DEEP will more than double the number of known TNOs with observational arcs of 24 hours or more, and increase by a factor of 10 or more the number of known small (<50 km) TNOs. We also describe our ancillary science goals, including measuring the mean shape distribution of very small main belt asteroids, and briefly outline a set of forthcoming papers that present further aspects of and preliminary results from the DEEP program. △ Less

Submitted 6 September, 2023; originally announced September 2023.

Comments: AJ, in press. First in a series of papers

Observational Characterization of Main-Belt Comet and Candidate Main-Belt Comet Nuclei

Authors: Henry H. Hsieh, Marco Micheli, Michael S. P. Kelley, Matthew M. Knight, Nicholas A. Moskovitz, Jana Pittichova, Scott S. Sheppard, Audrey Thirouin, Chadwick A. Trujillo, Richard J. Wainscoat, Robert J. Weryk, Quanzhi Ye

Abstract: We report observations of nine MBCs or candidate MBCs, most of which were obtained when the targets were apparently inactive. We find effective nucleus radii (assuming albedos of p_V=0.05+/-0.02) of r_n=(0.24+/-0.05) km for 238P/Read, r_n=(0.9+/-0.2) km for 313P/Gibbs, r_n=(0.6+/-0.1) km for 324P/La Sagra, r_n=(1.0+/-0.2) km for 426P/PANSTARRS, r_n=(0.5+/-0.1) km for 427P/ATLAS, r_n<(0.3+/-0.1) km… ▽ More We report observations of nine MBCs or candidate MBCs, most of which were obtained when the targets were apparently inactive. We find effective nucleus radii (assuming albedos of p_V=0.05+/-0.02) of r_n=(0.24+/-0.05) km for 238P/Read, r_n=(0.9+/-0.2) km for 313P/Gibbs, r_n=(0.6+/-0.1) km for 324P/La Sagra, r_n=(1.0+/-0.2) km for 426P/PANSTARRS, r_n=(0.5+/-0.1) km for 427P/ATLAS, r_n<(0.3+/-0.1) km for P/2016 J1-A (PANSTARRS), r_n<(0.17+/-0.04) km for P/2016 J1-B (PANSTARRS), r_n<(0.5+/-0.2) km for P/2017 S9 (PANSTARRS), and r_n=(0.4+/-0.1) km for P/2019 A3 (PANSTARRS). We identify evidence of activity in observations of 238P in 2021, and find similar inferred activity onset times and net initial mass loss rates for 238P during perihelion approaches in 2010, 2016, and 2021. P/2016 J1-A and P/2016 J1-B are also found to be active in 2021 and 2022, making them collectively the tenth MBC confirmed to be recurrently active near perihelion and therefore likely to be exhibiting sublimation-driven activity. The nucleus of 313P is found to have colors of g'-r'=0.52+/-0.05 and r'-i'=0.22+/-0.07, consistent with 313P being a Lixiaohua family member. We also report non-detections of P/2015 X6 (PANSTARRS), where we conclude that its current nucleus size is likely below our detection limits (r_n<0.3 km). Lastly, we find that of 17 MBCs or candidate MBCs for which nucleus sizes (or inferred parent body sizes) have been estimated, >80% have r_n<1.0 km, pointing to an apparent physical preference toward small MBCs, where we suggest that YORP spin-up may play a significant role in triggering and/or facilitating MBC activity. △ Less

Submitted 22 February, 2023; originally announced February 2023.

Comments: 27 pages, 14 figures. Accepted for publication in The Planetary Science Journal

A Deep and Wide Twilight Survey for Asteroids Interior to Earth and Venus

Authors: Scott S. Sheppard, David Tholen, Petr Pokorny, Marco Micheli, Ian Dell'Antonio, Shenming Fu, Chadwick Trujillo, Rachael Beaton, Scott Carlsten, Alex Drlica-Wagner, Clara Martinez-Vazquez, Sidney Mau, Toni Santana-Ros, Luidhy Santana-Silva, Cristobal Sifo, Sunil Simha, Audrey Thirouin, David Trilling, A. Katherina Vivas, Alfredo Zenteno

Abstract: We are conducting a survey using twilight time on the Dark Energy Camera with the Blanco 4m telescope in Chile to look for objects interior to Earth's and Venus' orbits. To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo type Near Earth Object (NEO) that crosses Earth's orbit… ▽ More We are conducting a survey using twilight time on the Dark Energy Camera with the Blanco 4m telescope in Chile to look for objects interior to Earth's and Venus' orbits. To date we have discovered two rare Atira/Apohele asteroids, 2021 LJ4 and 2021 PH27, which have orbits completely interior to Earth's orbit. We also discovered one new Apollo type Near Earth Object (NEO) that crosses Earth's orbit, 2022 AP7. Two of the discoveries likely have diameters greater than 1 km. 2022 AP7 is likely the largest Potentially Hazardous Asteroid (PHA) discovered in about eight years. To date we have covered 624 square degrees of sky near to and interior to the orbit of Venus. The average images go to 21.3 mags in the r-band, with the best images near 22nd mag. Our new discovery 2021 PH27 has the smallest semi-major axis known for an asteroid, 0.4617 au, and the largest general relativistic effects (53 arcseconds/century) known for any body in the Solar System. The survey has detected about 15 percent of all known Atira NEOs. We put strong constraints on any stable population of Venus co-orbital resonance objects existing, as well as the Atira and Vatira asteroid classes. These interior asteroid populations are important to complete the census of asteroids near Earth, including some of the most likely Earth impactors that cannot easily be discovered in other surveys. Comparing the actual population of asteroids found interior to Earth and Venus with those predicted to exist by extrapolating from the known population exterior to Earth is important to better understand the origin, composition and structure of the NEO population. △ Less

Submitted 13 September, 2022; originally announced September 2022.

Comments: In Press at The Astronomical Journal

Lightcurves and Rotations of Trans-Neptunian Objects in the 2:1 Mean Motion Resonance with Neptune

Authors: Audrey Thirouin, Scott S. Sheppard

Abstract: We report the rotational lightcurves of 21 trans-Neptunian objects (TNOs) in Neptune's 2:1 mean motion resonance obtained with the 6.5 m Magellan-Baade telescope and the 4.3 m Lowell Discovery Telescope. The main survey's goal is to find objects displaying a large lightcurve amplitude which is indicative of contact binaries or highly elongated objects. In our sample, two 2:1 resonant TNOs showed a… ▽ More We report the rotational lightcurves of 21 trans-Neptunian objects (TNOs) in Neptune's 2:1 mean motion resonance obtained with the 6.5 m Magellan-Baade telescope and the 4.3 m Lowell Discovery Telescope. The main survey's goal is to find objects displaying a large lightcurve amplitude which is indicative of contact binaries or highly elongated objects. In our sample, two 2:1 resonant TNOs showed a significant short-term lightcurve amplitude: 2002 VD$_{130}$ and (531074) 2012 DX$_{98}$. The full lightcurve of 2012 DX$_{98}$ infers a periodicity of 20.80$\pm$0.06h and amplitude of 0.56$\pm$0.03mag whereas 2002 VD$_{130}$ rotates in 9.85$\pm$0.07h with a 0.31$\pm$0.04mag lightcurve amplitude. Based on lightcurve morphology, we classify (531074) 2012 DX$_{98}$ as a likely contact binary, but 2002 VD$_{130}$ as a likely single elongated object. Based on our sample and the lightcurves reported in the literature, we estimate the lower percentage of nearly equal-sized contact binaries at only 7-14$\%$ in the 2:1 resonance, which is comparable to the low fraction reported for the dynamically Cold Classical trans-Neptunian objects. This low contact binary fraction in the 2:1 Neptune resonance is consistent with the lower estimate of the recent numerical modeling. We report the Sloan g', r', i' surface colors of 2002 VD$_{130}$ which is an ultra-red TNO whereas 2012 DX$_{98}$ is a very red object based on published surface colors. △ Less

Submitted 20 June, 2022; originally announced June 2022.

Comments: Accepted for publication, Planetary Science Journal

Physical Characterization of Main-Belt Comet (248370) 2005 QN173

Authors: Henry H. Hsieh, Colin O. Chandler, Larry Denneau, Alan Fitzsimmons, Nicolas Erasmus, Michael S. P. Kelley, Matthew M. Knight, Tim A. Lister, Jana Pittichova, Scott S. Sheppard, Audrey Thirouin, Chadwick A. Trujillo, Helen Usher, Edward Gomez, Joey Chatelain, Sarah Greenstreet, Tony Angel, Richard Miles, Paul Roche, Ben Wooding

Abstract: We report results from new and archival observations of the newly discovered active asteroid (248370) 2005 QN_137, which has been determined to be a likely main-belt comet based on a subsequent discovery that it is recurrently active near perihelion. From archival data analysis, we estimate g'-, r'-, i'-, and z'-band absolute magnitudes for the nucleus of H_g=16.62+/-0.13, H_r=16.12+/-0.10, H_i=16… ▽ More We report results from new and archival observations of the newly discovered active asteroid (248370) 2005 QN_137, which has been determined to be a likely main-belt comet based on a subsequent discovery that it is recurrently active near perihelion. From archival data analysis, we estimate g'-, r'-, i'-, and z'-band absolute magnitudes for the nucleus of H_g=16.62+/-0.13, H_r=16.12+/-0.10, H_i=16.05+/-0.11, and H_z=15.93+/-0.08, corresponding to nucleus colors of g'-r'=0.50+/-0.16, r'-i'=0.07+/-0.15, and i'-z'=0.12+/-0.14, an equivalent V-band absolute magnitude of H_V=16.32+/-0.08, and a nucleus radius of r_n=1.6+/-0.2 km (using a V-band albedo of p_V=0.054+/-0.012). Meanwhile, we find mean near-nucleus coma colors when 248370 was active of g'-r'=0.47+/-0.03, r'-i'=0.10+/-0.04, and i'-z'=0.05+/-0.05, and similar mean dust tail colors, suggesting that no significant gas coma is present. We find approximate ratios between the scattering cross-sections of near-nucleus dust (within 5000 km of the nucleus) and the nucleus of A_d/A_n=0.7+/-0.3 on 2016 July 22, and 1.8<A_d/A_n<2.9 in 2021 July and August. During the 2021 observation period, the coma declined in intrinsic brightness by ~0.35 mag (or ~25%) in 37 days, while the surface brightness of the dust tail remained effectively constant over the same period. Constraints derived from the sunward extent of the coma suggest that terminal velocities of ejected dust grains are extremely slow (~1 m/s for 1 micron particles), indicating that the observed dust emission may have been aided by rapid rotation of the nucleus lowering the effective escape velocity. △ Less

Submitted 29 September, 2021; originally announced September 2021.

Comments: 12 pages, 2 figures, accepted for publication in ApJ Letters (submitted version posted here; please contact first author for final accepted version)

Readability Research: An Interdisciplinary Approach

Authors: Sofie Beier, Sam Berlow, Esat Boucaud, Zoya Bylinskii, Tianyuan Cai, Jenae Cohn, Kathy Crowley, Stephanie L. Day, Tilman Dingler, Jonathan Dobres, Jennifer Healey, Rajiv Jain, Marjorie Jordan, Bernard Kerr, Qisheng Li, Dave B. Miller, Susanne Nobles, Alexandra Papoutsaki, Jing Qian, Tina Rezvanian, Shelley Rodrigo, Ben D. Sawyer, Shannon M. Sheppard, Bram Stein, Rick Treitman , et al. (3 additional authors not shown)

Abstract: Readability is on the cusp of a revolution. Fixed text is becoming fluid as a proliferation of digital reading devices rewrite what a document can do. As past constraints make way for more flexible opportunities, there is great need to understand how reading formats can be tuned to the situation and the individual. We aim to provide a firm foundation for readability research, a comprehensive frame… ▽ More Readability is on the cusp of a revolution. Fixed text is becoming fluid as a proliferation of digital reading devices rewrite what a document can do. As past constraints make way for more flexible opportunities, there is great need to understand how reading formats can be tuned to the situation and the individual. We aim to provide a firm foundation for readability research, a comprehensive framework for modern, multi-disciplinary readability research. Readability refers to aspects of visual information design which impact information flow from the page to the reader. Readability can be enhanced by changes to the set of typographical characteristics of a text. These aspects can be modified on-demand, instantly improving the ease with which a reader can process and derive meaning from text. We call on a multi-disciplinary research community to take up these challenges to elevate reading outcomes and provide the tools to do so effectively. △ Less

Submitted 20 July, 2021; originally announced July 2021.

Comments: This paper was generated collaboratively over the course of a series of online workshops, the results of which were extensively edited by Dr. Zoya Bylinskii, Dr. Ben D. Sawyer, and Dr. Benjamin Wolfe. Original illustrations by Bernard Kerr. Corresponding Author: Dr. Ben D. Sawyer

Stability of Neptune's distant resonances in the presence of Planet Nine

Authors: Matthew S. Clement, Scott S. Sheppard

Abstract: Trans-Neptunian Objects (TNOs) in the scattered disk with 50 < a < 100 au are thought to cluster near Neptune's n:1 resonances (e.g: 3:1, 4:1, and so on). While these objects spend lengthy periods of time at large heliocentric distances, if their perihelia remain less than around 40 au, their dynamical evolution is still largely coupled to Neptune's. Conversely, around a dozen extreme TNOs with a… ▽ More Trans-Neptunian Objects (TNOs) in the scattered disk with 50 < a < 100 au are thought to cluster near Neptune's n:1 resonances (e.g: 3:1, 4:1, and so on). While these objects spend lengthy periods of time at large heliocentric distances, if their perihelia remain less than around 40 au, their dynamical evolution is still largely coupled to Neptune's. Conversely, around a dozen extreme TNOs with a > 250 au and detached perihelia seem to exist in a regime where they are too distant to be affected by the giant planets, and too close for their dynamics to be governed by external forces. Recent work suggests that the apparent alignment of these orbits in physical space is a signature of gravitational shepherding by a distant massive planet. In this paper, we investigate the evolution of TNOs in each of Neptune's n:1 resonances between the 3:1 and 14:1. We conclude that both resonant and non-resonant objects beyond the 12:1 near ~157 au are removed rather efficiently via perturbations from the hypothetical Planet Nine. Additionally, we uncover a population of simulated TNOs with a < 100 au, 40 < q < 45 au and low inclinations that experience episodes of resonant interactions with both Neptune and Planet Nine. Finally, we simulate the evolution of observed objects with a > 100 au and identify several TNOs that are potentially locked in n:1 resonances with Neptune; including the most distant known resonant candidates 2014 JW80 and 2014 OS394 that appear to be in the 10:1 and 11:1 resonances, respectively. Our results suggest that the detection of similar remote objects might provide a useful constraint on hypotheses invoking the existence of additional distant planets. △ Less

Submitted 21 May, 2021; v1 submitted 3 May, 2021; originally announced May 2021.

Comments: 18 pages, 12 figures, 1 table, AJ in press, corrected minor typographical errors

The Reactivation of Main-Belt Comet 259P/Garradd (P/2008 R1)

Authors: Henry H. Hsieh, Masateru Ishiguro, Matthew M. Knight, Nicholas A. Moskovitz, Scott S. Sheppard, Chadwick A. Trujillo

Abstract: We present observations of main-belt comet 259P/Garradd from four months prior to its 2017 perihelion passage to five months after perihelion using the Gemini North and South telescopes. The object was confirmed to be active during this period, placing it among seven MBCs confirmed to have recurrent activity. We find an average net pre-perihelion dust production rate for 259P in 2017 of dM/dt = 4.… ▽ More We present observations of main-belt comet 259P/Garradd from four months prior to its 2017 perihelion passage to five months after perihelion using the Gemini North and South telescopes. The object was confirmed to be active during this period, placing it among seven MBCs confirmed to have recurrent activity. We find an average net pre-perihelion dust production rate for 259P in 2017 of dM/dt = 4.6+/-0.2 kg/s (assuming grain densities of rho = 2500 kg/m^3 and a mean effective particle size of a_d = 2 mm) and a best-fit start date of detectable activity of 2017 April 22+/-1, when the object was at a heliocentric distance of r_h = 1.96-/+0.03 au and a true anomaly of nu = 313.9+/-0.4 deg. We estimate the effective active fraction of 259P's surface area to be from f_act ~ 7x10^-3 to f_act ~ 6x10^-2 (corresponding to effective active areas of A_act ~ 8x10^3 m^2 to A_act ~ 7x10^4 m^2) at the start of its 2017 active period. A comparison of estimated total dust masses measured for 259P in 2008 and 2017 shows no evidence of changes in activity strength between the two active apparitions. The heliocentric distance of 259P's activity onset point is much smaller than those of other MBCs, suggesting that its ice reservoirs may be located at greater depths than on MBCs farther from the Sun, increasing the time needed for a solar irradiation-driven thermal wave to reach subsurface ice. We suggest that deeper ice on 259P could be a result of more rapid ice depletion caused by the object's closer proximity to the Sun compared to other MBCs. △ Less

Submitted 11 February, 2021; originally announced February 2021.

Comments: 12 pages, 6 figures. Accepted for publication in The Planetary Science Journal

ASASSN-14ko is a Periodic Nuclear Transient in ESO 253-G003

Authors: Anna V. Payne, Benjamin J. Shappee, Jason T. Hinkle, Patrick J. Vallely, Christopher S. Kochanek, Thomas W. -S. Holoien, Katie Auchettl, K. Z. Stanek, Todd A. Thompson, Jack M. M. Neustadt, Michael A. Tucker, James D. Armstrong, Joseph Brimacombe, Paulo Cacella, Robert Cornect, Larry Denneau, Michael M. Fausnaugh, Heather Flewelling, Dirk Grupe, A. N. Heinze, Laura A. Lopez, Berto Monard, Jose L. Prieto, Adam C. Schneider, Scott S. Sheppard , et al. (2 additional authors not shown)

Abstract: We present the discovery that ASASSN-14ko is a periodically flaring AGN at the center of the galaxy ESO 253-G003. At the time of its discovery by the All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a supernova close to the nucleus. The subsequent six years of V- and g-band ASAS-SN observations reveal that ASASSN-14ko has nuclear flares occurring at regular intervals. The se… ▽ More We present the discovery that ASASSN-14ko is a periodically flaring AGN at the center of the galaxy ESO 253-G003. At the time of its discovery by the All-Sky Automated Survey for Supernovae (ASAS-SN), it was classified as a supernova close to the nucleus. The subsequent six years of V- and g-band ASAS-SN observations reveal that ASASSN-14ko has nuclear flares occurring at regular intervals. The seventeen observed outbursts show evidence of a decreasing period over time, with a mean period of $P_0 = 114.2 \pm 0.4$ days and a period derivative of $\dot{P} = -0.0017\pm0.0003$. The most recent outburst in May 2020, which took place as predicted, exhibited spectroscopic changes during the rise and a had a UV bright, blackbody spectral energy distribution similar to tidal disruption events (TDEs). The X-ray flux decreased by a factor of 4 at the beginning of the outburst and then returned to its quiescent flux after ~8 days. TESS observed an outburst during Sectors 4-6, revealing a rise time of $5.60 \pm 0.05$ days in the optical and a decline that is best fit with an exponential model. We discuss several possible scenarios to explain ASASSN-14ko's periodic outbursts, but currently favor a repeated partial TDE. The next outbursts should peak in the optical on UT 2020-09-7.4$ \pm $1.1 and UT 2020-12-26.5$ \pm $1.4. △ Less

Submitted 7 September, 2020; originally announced September 2020.

Comments: 26 pages, 15 figures, 7 tables. Will be submitted to ApJ. The latest flare is currently ongoing, as we predicted

A Deep Search for Stable Venus Co-Orbital Asteroids: Limits on The Population

Authors: Petr Pokorny, Marc J. Kuchner, Scott S. Sheppard

Abstract: A stable population of objects co-orbiting with Venus was recently hypothesized in order to explain the existence of Venus's co-orbital dust ring. We conducted a 5 day twilight survey for these objects with the Cerro-Tololo Inter-American Observatory (CTIO) 4 meter telescope covering about 35 unique square degrees to 21 mag in the $r$-band. Our survey provides the most stringent limit so far on th… ▽ More A stable population of objects co-orbiting with Venus was recently hypothesized in order to explain the existence of Venus's co-orbital dust ring. We conducted a 5 day twilight survey for these objects with the Cerro-Tololo Inter-American Observatory (CTIO) 4 meter telescope covering about 35 unique square degrees to 21 mag in the $r$-band. Our survey provides the most stringent limit so far on the number of Venus co-orbital asteroids; it was capable of detecting $5\%$ of the entire population of those asteroids brighter than 21 magnitude. We estimate an upper limit on the number of co-orbital asteroids brighter than 21 magnitude (approximately 400-900 m in diameter depending on the asteroid albedo) to be $N=18^{+30}_{-14}$. Previous studies estimated the mass of the observed dust ring co-orbiting with Venus to be equivalent to an asteroid with a 2 km diameter ground to dust. Our survey estimates $<6$ asteroids larger than 2 km. This implies the following possibilities: that Venus co-orbitals are non-reflective at the observed phase angles, have a very low albedo ($<1\%$), or that the Venus co-orbital dust ring has a source other than asteroids co-orbiting Venus. We discuss this result, and as an aid to future searches, we provide predictions for the spatial, visual magnitude, and number density distributions of stable Venus co-orbitals based on the dynamics of the region and magnitude estimates for various asteroid types. △ Less

Submitted 5 August, 2020; v1 submitted 3 August, 2020; originally announced August 2020.

Comments: Accepted to PSJ. 19 pages, 8 figures, 4 tables

The Geology and Geophysics of Kuiper Belt Object (486958) Arrokoth

Authors: J. R. Spencer, S. A. Stern, J. M. Moore, H. A. Weaver, K. N. Singer, C. B. Olkin, A. J. Verbiscer, W. B. McKinnon, J. Wm. Parker, R. A. Beyer, J. T. Keane, T. R. Lauer, S. B. Porter, O. L. White, B. J. Buratti, M. R. El-Maarry, C. M. Lisse, A. H. Parker, H. B. Throop, S. J. Robbins, O. M. Umurhan, R. P. Binzel, D. T. Britt, M. W. Buie, A. F. Cheng , et al. (53 additional authors not shown)

Abstract: The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, are primitive objects preserving information about Solar System formation. The New Horizons spacecraft flew past one of these objects, the 36 km long contact binary (486958) Arrokoth (2014 MU69), in January 2019. Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger t… ▽ More The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, are primitive objects preserving information about Solar System formation. The New Horizons spacecraft flew past one of these objects, the 36 km long contact binary (486958) Arrokoth (2014 MU69), in January 2019. Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters diameter) within a radius of 8000 km, and has a lightly-cratered smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism. △ Less

Submitted 1 April, 2020; originally announced April 2020.

Journal ref: Science, 367, aay3999 (2020)

Observational Investigation of the 2013 Near-Earth Encounter by Asteroid (367943) Duende

Authors: Nicholas Moskovitz, Conor Benson, Daniel Scheeres, Thomas Endicott, David Polishook, Richard Binzel, Francesca DeMeo, William Ryan, Eileen Ryan, Mark Willman, Carl Hergenrother, Arie Verneer, Tim Lister, Peter Birtwhistle, Amanda Sickafoose, Takahiro Nagayama, Alan Gilmore, Pamela Kilmartin, Susan Bennechi, Scott Sheppard, Franck Marchis, Thomas Augusteijn, Olesja Smirnova

Abstract: On 15 February 2013, the asteroid 367943 Duende (2012 DA14) experienced a near-Earth encounter at an altitude of 27,700 km or 4.2 Earth radii. We present here the results of an extensive, multi-observatory campaign designed to probe for spectral and/or rotational changes to Duende due to gravitational interactions with the Earth during the flyby. Our spectral data reveal no changes within the syst… ▽ More On 15 February 2013, the asteroid 367943 Duende (2012 DA14) experienced a near-Earth encounter at an altitude of 27,700 km or 4.2 Earth radii. We present here the results of an extensive, multi-observatory campaign designed to probe for spectral and/or rotational changes to Duende due to gravitational interactions with the Earth during the flyby. Our spectral data reveal no changes within the systematic uncertainties of the data. Post-flyby lightcurve photometry places strong constraints on the rotation state of Duende, showing that it is in non-principal axis rotation with fundamental periods of P_1 = 8.71 +/- 0.03 and P_2 = 23.7 +/- 0.2 hours. Multiple lightcurve analysis techniques, coupled with theoretical considerations and delay-doppler radar imaging, allows us to assign these periods to specific rotational axes of the body. In particular we suggest that Duende is now in a non-principal, short axis mode rotation state with a precessional period equal to P_1 and oscillation about the symmetry axis at a rate equal to P_2. Temporal and signal-to-noise limitations inherent to the pre-flyby photometric dataset make it difficult to definitively diagnose whether these periods represent a change imparted due to gravitational torques during the flyby. However, based on multiple analysis techniques and a number of plausibility arguments, we suggest that Duende experienced a rotational change during the planetary encounter with an increase in its precessional rotation period. Our preferred interpretation of the available data is that the precession rate increased from 8.4 hours prior to the flyby to 8.7 hours afterwards. A companion paper by Benson et al. (2019) provides a more detailed dynamical analysis of this event and compares the data to synthetic lightcurves computed from a simple shape model of Duende. (abbreviated abstract) △ Less

Submitted 1 November, 2019; originally announced November 2019.

Comments: 50 pages (double spaced), 12 figures, 5 tables, accepted to Icarus

Colors of Trans-Neptunian Contact Binaries

Authors: Audrey Thirouin, Scott S. Sheppard

Abstract: The g'r'i' colors of seven likely and potential contact binaries in the Kuiper belt were acquired with the Magellan-Baade telescope and combined with colors from the literature to understand contact binary surfaces. The likely and potential contact binaries discovered in the dynamically Cold Classical population display very-red/ultra-red colors. Such a color is common in this sub-population and i… ▽ More The g'r'i' colors of seven likely and potential contact binaries in the Kuiper belt were acquired with the Magellan-Baade telescope and combined with colors from the literature to understand contact binary surfaces. The likely and potential contact binaries discovered in the dynamically Cold Classical population display very-red/ultra-red colors. Such a color is common in this sub-population and infers that the Cold Classical contact binaries were formed in-situ. The likely contact binaries found in several mean motion resonances with Neptune have colors from moderately to ultra-red suggesting different formation regions. Among the nine contact binaries discovered in resonances, five have very-red/ultra-red colors and four have moderately-red surfaces. Based on the very-red/ultra-red colors and low to moderate inclination of the contact binaries in resonances, these contact binaries are maybe escaped dynamically Cold Classicals that are now trapped in resonances. Moderately-red surfaces are common in diverse sub-populations of the Kuiper belt and thus pinpointing their origin is difficult though they are most likely captured objects formed in the giant planet area. Finally, for the contact binary population we report an anti-correlation between inclination and g'-r', as noticed in the rest of this belt. We also have hints for trends between eccentricity, perihelion distance, rotational period and g'-r', but as we are still dealing with a limited sample, additional data are required to confirm them. △ Less

Submitted 5 June, 2019; originally announced June 2019.

Comments: In press, AJ

Lightcurves and Rotational Properties of the Pristine Cold Classical Kuiper Belt Objects

Authors: Audrey Thirouin, Scott S. Sheppard

Abstract: We present a survey on the rotational and physical properties of the dynamically low inclination Cold Classical trans-Neptunian objects. The Cold Classicals (CCs) are primordial planetesimals and contain relevant information about the early phase of our Solar System and planet formation over the first 100 million years after the formation of the Sun. Our project makes use of the Magellan and the L… ▽ More We present a survey on the rotational and physical properties of the dynamically low inclination Cold Classical trans-Neptunian objects. The Cold Classicals (CCs) are primordial planetesimals and contain relevant information about the early phase of our Solar System and planet formation over the first 100 million years after the formation of the Sun. Our project makes use of the Magellan and the Lowell's Discovery Channel Telescopes for photometric purposes. We obtained partial/complete lightcurves for 42 CCs. We use statistical tests to derive general properties about the shape and rotational frequency distributions of the CC population, and infer that the CCs have slower rotations and are more elongated/deformed than the other trans-Neptunian objects. Based on the available full lightcurves, the mean rotational period of the CC population is 9.48$\pm$1.53h whereas the mean period of the rest of the trans-Neptunian objects is 8.45$\pm$0.58h. About 65% of the trans-Neptunian objects (excluding the CCs) have a lightcurve amplitude below 0.2mag compared to the 36% of CCs with small amplitude. We present the full lightcurve of one new likely contact binary: 2004 VC131 with a potential density of 1gcc for a mass ratio of 0.4. We also have hints that 2004 MU8 and 2004 VU75 are maybe potential contact binaries based on their sparse lightcurves but more data are needed to confirm such a find. Assuming equal-sized binaries, we find that only ~10-25% of the Cold Classicals could be contact binaries, suggesting that there is a deficit of contact binaries in this population compared to previous estimates and compared to the abundant (~40-50%) possible contact binaries in the 3:2 resonant population. This estimate is a lower limit and will increase if non equal-sized contact binaries are also considered. Finally, we put in context the early results of the New Horizons flyby of (486958) 2014 MU69. △ Less

Submitted 3 April, 2019; originally announced April 2019.

Comments: AJ, In press

A Northern Ecliptic Survey for Solar System Science

Authors: Megan E. Schwamb, Kathryn Volk, Hsing Wen, Lin, Michael S. P. Kelley, Michele T. Bannister, Henry H. Hsieh, R. Lynne Jones, Michael Mommert, Colin Snodgrass, Darin Ragozzine, Steven R. Chesley, Scott S. Sheppard, Mario Juric, Marc W. Buie

Abstract: Making an inventory of the Solar System is one of the four fundamental science requirements for the Large Synoptic Survey Telescope (LSST). The current baseline footprint for LSST's main Wide-Fast-Deep (WFD) Survey observes the sky below 0$^\circ$ declination, which includes only half of the ecliptic plane. Critically, key Solar System populations are asymmetrically distributed on the sky: they wi… ▽ More Making an inventory of the Solar System is one of the four fundamental science requirements for the Large Synoptic Survey Telescope (LSST). The current baseline footprint for LSST's main Wide-Fast-Deep (WFD) Survey observes the sky below 0$^\circ$ declination, which includes only half of the ecliptic plane. Critically, key Solar System populations are asymmetrically distributed on the sky: they will be entirely missed, or only partially mapped, if only the WFD occurs. We propose a Northern Ecliptic Spur (NES) mini survey, observing the northern sky up to +10$^\circ$ ecliptic latitude, to maximize Solar System science with LSST. The mini survey comprises a total area of $\sim$5800 deg$^2$/604 fields, with 255 observations/field over the decade, split between g,r, and z bands. Our proposed survey will 1) obtain a census of main-belt comets; 2) probe Neptune's past migration history, by exploring the resonant structure of the Kuiper belt and the Neptune Trojan population; 3) explore the origin of Inner Oort cloud objects and place significant constraints on the existence of a hypothesized planet beyond Neptune; and 4) enable precise predictions of KBO stellar occultations. These high-ranked science goals of the Solar System Science Collaboration are only achievable with this proposed northern survey. △ Less

Submitted 3 December, 2018; originally announced December 2018.

Comments: White Paper submitted in response to the Call for LSST Cadence Optimization White Papers

MARVEL Analysis of the Measured High-Resolution Rovibronic Spectra of 90Zr16O

Authors: Laura K McKemmish, Jasmin Borsovszky, Katie L Goodhew, Samuel Sheppard, Aphra F V Bennett, Alfie D J Martin, Amrik Singh, Callum A J Sturgeon, Tibor Furtenbacher, Attila G Csaszar, Jonathan Tennyson

Abstract: Zirconium oxide(ZrO) is an important astrophysical molecule that defines the S-star classification class for cool giant stars. Accurate, empirical rovibronic energy levels, with associated labels and uncertainties, are reported for 9 low-lying electronic states of the diatomic 90Zr16O molecule. These 8088 empirical energy levels are determined using the Marvel (Measured Active Rotational-Vibration… ▽ More Zirconium oxide(ZrO) is an important astrophysical molecule that defines the S-star classification class for cool giant stars. Accurate, empirical rovibronic energy levels, with associated labels and uncertainties, are reported for 9 low-lying electronic states of the diatomic 90Zr16O molecule. These 8088 empirical energy levels are determined using the Marvel (Measured Active Rotational-Vibrational Energy Levels) algorithm with 23 317 input assigned transition frequencies, 22 549 of which were validated. A temperature-dependent partition function is presented alongside updated spectroscopic constants for the 9 low-lying electronic states. △ Less

Submitted 4 November, 2018; originally announced November 2018.

Journal ref: The Astrophysical Journal 867.1 (2018): 33

A New High Perihelion Inner Oort Cloud Object: 2015 TG387

Authors: Scott Sheppard, Chadwick Trujillo, David Tholen, Nathan Kaib

Abstract: Inner Oort Cloud objects (IOCs) are Trans-Plutonian for their entire orbits. They are beyond the strong gravitational influences of the known planets yet close enough to the Sun that outside forces are minimal. Here we report the discovery of the third known IOC after Sedna and 2012 VP113, called 2015 TG387. 2015 TG387 has a perihelion of $65 \pm 1$ au and semi-major axis of $1170 \pm 70$ au. The… ▽ More Inner Oort Cloud objects (IOCs) are Trans-Plutonian for their entire orbits. They are beyond the strong gravitational influences of the known planets yet close enough to the Sun that outside forces are minimal. Here we report the discovery of the third known IOC after Sedna and 2012 VP113, called 2015 TG387. 2015 TG387 has a perihelion of $65 \pm 1$ au and semi-major axis of $1170 \pm 70$ au. The longitude of perihelion angle, $\barω$, for 2015 TG387 is between that of Sedna and 2012 VP113, and thus similar to the main group of clustered extreme trans-Neptunian objects (ETNOs), which may be shepherded into similar orbital angles by an unknown massive distant planet, called Planet X or Planet Nine. 2015 TG387's orbit is stable over the age of the solar system from the known planets and Galactic tide. When including outside stellar encounters over 4 Gyrs, 2015 TG387's orbit is usually stable, but its dynamical evolution depends on the stellar encounter scenarios used. Surprisingly, when including a massive Planet X beyond a few hundred au on an eccentric orbit that is anti-aligned in longitude of perihelion with most of the known ETNOs, we find 2015 TG387 is typically stable for Planet X orbits that render the other ETNOs stable as well. Notably, 2015 TG387's argument of perihelion is constrained and its longitude of perihelion librates about 180 degs from Planet X's longitude of perihelion, keeping 2015 TG387 anti-aligned with Planet X over the age of the solar system. We find a power law slope near 3 for the semi-major axis distribution of IOCs, meaning there are many more high than low semi-major axis IOCs. There are about 2 million IOCs larger than 40 km, giving a mass of $10^{22}$ kg. The IOCs inclination distribution is similar to the scattered disk, with an average inclination of 19 degs. △ Less

Submitted 19 February, 2019; v1 submitted 28 September, 2018; originally announced October 2018.

Comments: Accepted to The Astronomical Journal

The 2016 Reactivations of Main-Belt Comets 238P/Read and 288P/(300163) 2006 VW139

Authors: Henry H. Hsieh, Masateru Ishiguro, Yoonyoung Kim, Matthew M. Knight, Zhong-Yi Lin, Marco Micheli, Nicholas A. Moskovitz, Scott S. Sheppard, Audrey Thirouin, Chadwick A. Trujillo

Abstract: We report observations of the reactivations of main-belt comets 238P/Read and 288P/(300163) 2006 VW139, that also track the evolution of each object's activity over several months in 2016 and 2017. We additionally identify and analyze archival SDSS data showing 288P to be active in 2000, meaning that both 238P and 288P have now each been confirmed to be active near perihelion on three separate occ… ▽ More We report observations of the reactivations of main-belt comets 238P/Read and 288P/(300163) 2006 VW139, that also track the evolution of each object's activity over several months in 2016 and 2017. We additionally identify and analyze archival SDSS data showing 288P to be active in 2000, meaning that both 238P and 288P have now each been confirmed to be active near perihelion on three separate occasions. From data obtained of 288P from 2012-2015 when it appeared inactive, we find best-fit R-band H,G phase function parameters of H_R=16.80+/-0.12 mag and G_R=0.18+/-0.11, corresponding to effective component radii of r_c=0.80+/-0.04 km, assuming a binary system with equally-sized components. Fitting linear functions to ejected dust masses inferred for 238P and 288P soon after their observed reactivations in 2016, we find an initial average net dust production rate of 0.7+/-0.3 kg/s and a best-fit start date of 2016 March 11 (when the object was at a true anomaly of -63 deg) for 238P, and an initial average net dust production rate of 5.6+/-0.7 kg/s and a best-fit start date of 2016 August 5 (when the object was at a true anomaly of -27 deg) for 288P. Applying similar analyses to archival data, we find similar start points for previous active episodes for both objects, suggesting that minimal mantle growth or ice recession occurred between the active episodes in question. Some changes in dust production rates between active episodes are detected, however. More detailed dust modeling is suggested to further clarify the process of activity evolution in main-belt comets. △ Less

Submitted 26 September, 2018; originally announced September 2018.

Comments: 21 pages, 9 figures, accepted by AJ

The Albedos, Sizes, Colors and Satellites of Dwarf Planets Compared with Newly Measured Dwarf Planet 2013 FY27

Authors: Scott Sheppard, Yanga Fernandez, Arielle Moullet

Abstract: 2013 FY27 is the ninth intrinsically brightest Trans-Neptunian Object (TNO). We observed 2013 FY27 at thermal wavelengths with ALMA and in the optical with Magellan to determine its size and albedo for the first time and compare it to other dwarf planets. The geometric albedo of 2013 FY27 was found to be 0.17 -0.030+0.045, giving an effective diameter of D = 765 +80-85 km. 2013 FY27 has a size wit… ▽ More 2013 FY27 is the ninth intrinsically brightest Trans-Neptunian Object (TNO). We observed 2013 FY27 at thermal wavelengths with ALMA and in the optical with Magellan to determine its size and albedo for the first time and compare it to other dwarf planets. The geometric albedo of 2013 FY27 was found to be 0.17 -0.030+0.045, giving an effective diameter of D = 765 +80-85 km. 2013 FY27 has a size within the transition region between the largest few TNOs that have higher albedos and higher densities than smaller TNOs. No significant short-term optical light curve was found, with variations less than 0.06 mags over hours and days. The Sloan optical colors of 2013 FY27 are g-r=0.76 +-0.02 and r-i=0.31 +-0.03 mags, which is a moderately red color. This color is different than the neutral or ultra-red colors found for the ten largest TNOs, making 2013 FY27 one of the largest known moderately red TNOs, which only start to be seen, and in abundance, at diameters less than 800 km. This suggests something physically different might be associated with TNOs larger than 800 km. It could be that moderately red surfaces are older or less ice rich and TNOs larger than 800 km have fresher surfaces or are able to hold onto more volatile ices. Its also possible TNOs larger than 800 km are more fully differentiated, giving them different surface compositions. A satellite at 0.17 arcsec away and 3.0 +-0.2 mags fainter than 2013 FY27 was found through Hubble Space Telescope observations. Almost all the largest TNOs have satellites, and the relative small size of 2013 FY27's satellite suggests it was created through a direct collision, similar to satellites known around the largest TNOs. Assuming the satellite has a similar albedo as the primary, it is about 190 km in diameter, making the primary D = 740 +85-90 km. △ Less

Submitted 6 September, 2018; originally announced September 2018.

Comments: AJ

New Jupiter Satellites and Moon-Moon Collisions

Authors: Scott Sheppard, Gareth Williams, David Tholen, Chadwick Trujillo, Marina Brozovic, Audrey Thirouin, Maxime Devogele, Dora Fohring, Robert Jacobson, Nicholas Moskovitz

Abstract: We report the discovery of 12 new satellites of Jupiter, giving Jupiter 79 known satellites. The new finds are between 23rd-24th mag in the r-band and 1-3 km in diameter assuming dark albedos. Nine of the discoveries are in the distant retrograde satellite groupings. Two of the new satellites are in the closer Himalia prograde group near 28 degrees in inclination. S/2016 J2, nicknamed Valetudo, ha… ▽ More We report the discovery of 12 new satellites of Jupiter, giving Jupiter 79 known satellites. The new finds are between 23rd-24th mag in the r-band and 1-3 km in diameter assuming dark albedos. Nine of the discoveries are in the distant retrograde satellite groupings. Two of the new satellites are in the closer Himalia prograde group near 28 degrees in inclination. S/2016 J2, nicknamed Valetudo, has an orbit unlike any other known outer satellite and is the most distant prograde satellite around any planet at 0.36 Hill radii. Numerical simulations show S/2016 J2 is very stable, with average and range of i=34.2+-3 deg, e=0.216+-0.125, and a=18.9+-0.7 million km over 100 Myrs. Our stability simulations show a S/2016 J2 like orbit would be stable out to a=21.8 million km or 0.41 Hill radii, but no further, unlike more distant and eccentric retrograde satellites. S/2016 J2's large semi-major axis means it significantly overlaps the orbits of the distant retrogrades. A prograde-retrograde moon-moon collision between outer satellites of Jupiter has likely happened over the age of the solar system. △ Less

Submitted 3 September, 2018; originally announced September 2018.

Comments: Published Research Notes AAS

SAFARI: Searching Asteroids For Activity Revealing Indicators

Authors: Colin Orion Chandler, Anthony M. Curtis, Michael Mommert, Scott S. Sheppard, Chadwick A. Trujillo

Abstract: Active asteroids behave dynamically like asteroids but display comet-like comae. These objects are poorly understood, with only about 30 identified to date. We have conducted one of the deepest systematic searches for asteroid activity by making use of deep images from the Dark Energy Camera (DECam) ideally suited to the task. We looked for activity indicators amongst 11,703 unique asteroids extra… ▽ More Active asteroids behave dynamically like asteroids but display comet-like comae. These objects are poorly understood, with only about 30 identified to date. We have conducted one of the deepest systematic searches for asteroid activity by making use of deep images from the Dark Energy Camera (DECam) ideally suited to the task. We looked for activity indicators amongst 11,703 unique asteroids extracted from 35,640 images. We detected three previously-identified active asteroids ((62412), (1) Ceres and (779) Nina), though only (62412) showed signs of activity. Our activity occurrence rate of 1 in 11,703 is consistent with the prevailing 1 in 10,000 activity occurrence rate estimate. Our proof of concept demonstrates 1) our novel informatics approach can locate active asteroids and 2) DECam data are well-suited to the search for active asteroids. △ Less

Submitted 2 July, 2018; originally announced July 2018.

Comments: 25 pages, 6 figures, 5 tables

The Reactivation and Nucleus Characterization of Main-Belt Comet 358P/PANSTARRS (P/2012 T1)

Authors: Henry H. Hsieh, Masateru Ishiguro, Matthew M. Knight, Marco Micheli, Nicholas A. Moskovitz, Scott S. Sheppard, Chadwick A. Trujillo

Abstract: We present observations of main-belt comet 358P/PANSTARRS (P/2012 T1) obtained using the Gemini South telescope from 2017 July to 2017 December, as the object approached perihelion for the first time since its discovery. We find best-fit IAU phase function parameters of H_R=19.5+/-0.2 mag and G_R=-0.22+/-0.13 for the nucleus, corresponding to an effective radius of r_N=0.32+/-0.03 km (assuming an… ▽ More We present observations of main-belt comet 358P/PANSTARRS (P/2012 T1) obtained using the Gemini South telescope from 2017 July to 2017 December, as the object approached perihelion for the first time since its discovery. We find best-fit IAU phase function parameters of H_R=19.5+/-0.2 mag and G_R=-0.22+/-0.13 for the nucleus, corresponding to an effective radius of r_N=0.32+/-0.03 km (assuming an albedo of p_R=0.05). The object appears significantly brighter (by >1 mag) than expected starting in 2017 November, while a faint dust tail oriented approximately in the antisolar direction is also observed on 2017 December 18. We conclude that 358P has become active again for the first time since its previously observed active period in 2012-2013. These observations make 358P the seventh main-belt comet candidate confirmed to exhibit recurrent activity near perihelion with intervening inactivity away from perihelion, strongly indicating that its activity is sublimation-driven. Fitting a linear function to the ejected dust masses inferred for 358P in 2017 when it is apparently active, we find an average net dust production rate of 2.0+/-0.6 kg/s (assuming a mean effective particle radius of 1 mm) and an estimated activity start date of 2017 November 8+/-4 when the object was at a true anomaly of 316+/-1 deg and a heliocentric distance of R=2.54 AU. Insufficient data is currently available to ascertain whether activity strength has changed between the object's 2012-2013 and 2017 active periods. Further observations are therefore highly encouraged during the object's upcoming observing window (2018 August through 2019 May). △ Less

Submitted 23 May, 2018; originally announced May 2018.

Comments: 13 pages, 5 figures, accepted by AJ

The Plutino population: An Abundance of contact binaries

Authors: Audrey Thirouin, Scott S. Sheppard

Abstract: We observed twelve Plutinos over two separated years with the 4.3m Lowell's Discovery Channel Telescope. Here, we present the first lightcurve data for those objects. Three of them (2014JL$_{80}$, 2014JO$_{80}$, 2014JQ$_{80}$) display a large lightcurve amplitude explainable by a single elongated object, but are most likely caused by a contact binary system due to their lightcurves morphology. The… ▽ More We observed twelve Plutinos over two separated years with the 4.3m Lowell's Discovery Channel Telescope. Here, we present the first lightcurve data for those objects. Three of them (2014JL$_{80}$, 2014JO$_{80}$, 2014JQ$_{80}$) display a large lightcurve amplitude explainable by a single elongated object, but are most likely caused by a contact binary system due to their lightcurves morphology. These potential contact binaries have rotational periods from 6.3h to 34.9h and peak-to-peak lightcurve variability between 0.6 and 0.8mag. We present partial lightcurves allowing us to constrain the lightcurve amplitude and the rotational period of another nine Plutinos. By merging our data with the literature, we estimate that up to $\sim$40$\%$ of the Plutinos could be contact binaries. Interestingly, we found that all the suspected contact binaries in the 3:2 resonance are small with absolute magnitude H$>$6mag. Based on our sample and the literature, up to $\sim$50$\%$ of the small Plutinos are potential contact binaries. △ Less

Submitted 25 April, 2018; originally announced April 2018.

Comments: In press, AJ

The Excited Spin State of 1I/2017 U1 `Oumuamua

Authors: Michael J. S. Belton, Olivier R. Hainaut, Karen J. Meech, Beatrice E. A. Mueller, Jan T. Kleyna, Harold A. Weaver, Marc W. Buie, Michał Drahus, Piotr Guzik, Richard J. Wainscoat, Wacław Waniak, Barbara Handzlik, Sebastian Kurowski, Siyi Xu, Scott S. Sheppard, Marco Micheli, Harald Ebeling, Jacqueline V. Keane

Abstract: We show that `Oumuamua's excited spin could be in a high energy LAM state, which implies that its shape could be far from the highly elongated shape found in previous studies. CLEAN and ANOVA algorithms are used to analyze `Oumuamua's lightcurve using 818 observations over 29.3~days. Two fundamental periodicities are found at frequencies (2.77$\pm$0.11) and (6.42$\pm$0.18)~cycles/day, correspondin… ▽ More We show that `Oumuamua's excited spin could be in a high energy LAM state, which implies that its shape could be far from the highly elongated shape found in previous studies. CLEAN and ANOVA algorithms are used to analyze `Oumuamua's lightcurve using 818 observations over 29.3~days. Two fundamental periodicities are found at frequencies (2.77$\pm$0.11) and (6.42$\pm$0.18)~cycles/day, corresponding to (8.67$\pm$0.34)~h and (3.74$\pm$0.11)~h, respectively. The phased data show that the lightcurve does not repeat in a simple manner, but approximately shows a double minimum at 2.77~cycles/day and a single minimum at 6.42~cycles/day. This is characteristic of an excited spin state. `Oumuamua could be spinning in either the long (LAM) or short (SAM) axis mode. For both, the long axis precesses around the total angular momentum vector with an average period of (8.67$\pm$0.34)~h. For the three LAMs we have found, the possible rotation periods around the long axis are 6.58, 13.15, or 54.48~h, with 54.48~h being the most likely. `Oumuamua may also be nutating with respective periods of half of these values. We have also found two possible SAM states where `Oumuamua oscillates around the long axis with possible periods at 13.15 and 54.48~h, the latter as the most likely. In this case any nutation will occur with the same periods. Determination of the spin state, the amplitude of the nutation, the direction of the TAMV, and the average total spin period may be possible with a direct model fit to the lightcurve. We find that `Oumuamua is "cigar-shaped"', if close to its lowest rotational energy, and an extremely oblate spheroid if close to its highest energy state for its total angular momentum. △ Less

Submitted 10 April, 2018; originally announced April 2018.

Comments: 8 pages, 3 figures

Journal ref: The Astrophysical Journal Letters, Volume 856, Issue 2, article id. L21, 6 pp. (2018)

New Y and T dwarfs from WISE identified by Methane Imaging

Authors: C. G. Tinney, J. Davy Kirkpatrick, Jacqueline K. Faherty, Gregory N. Mace, Mike Cushing, Christopher R. Gelino, Adam J. Burgasser, Scott S. Sheppard, Edward L. Wright

Abstract: We identify new Y- and T-type brown dwarfs from the WISE All Sky data release using images obtained in filters that divide the traditional near-infrared H and J bands into two halves -- specifically CH4s & CH4l in the H and J2 & J3 in the J. This proves to be very effective at identifying cool brown dwarfs via the detection of their methane absorption, as well as providing preliminary classificati… ▽ More We identify new Y- and T-type brown dwarfs from the WISE All Sky data release using images obtained in filters that divide the traditional near-infrared H and J bands into two halves -- specifically CH4s & CH4l in the H and J2 & J3 in the J. This proves to be very effective at identifying cool brown dwarfs via the detection of their methane absorption, as well as providing preliminary classification using methane colours and WISE-to-near-infrared colours. New and updated calibrations between T/Y spectral types and CH4s-CH4l, J3-W2, and CH4s-W2 colours are derived, producing classification estimates good to a few spectral sub-types. We present photometry for a large sample of T and Y dwarfs in these filters, together with spectroscopy for 23 new ultra-cool dwarfs - two Y dwarfs and twenty one T dwarfs. We identify a further 8 new cool brown dwarfs, which we have high confidence are T dwarfs based on their methane photometry. We find that, for objects observed on a 4m-class telescope at J band magnitudes of ~20 or brighter, CH4s-CH4l is the more powerful colour for detecting objects and then estimating spectral types. Due to the lower sky background in the J-band, the J3 and J2 bands are more useful for identifying fainter cool dwarfs at J>22. The J3-J2 colour is poor at estimating spectral types. But fortunately, once J3-J2 confirms that an object is a cool dwarf, the J3-W2 colour is very effective at estimating approximate spectral types. △ Less

Submitted 1 April, 2018; originally announced April 2018.

Comments: 29 pages, 6 figures. To appear in the Astrophysical Journal Supplement

A possible dynamically Cold Classical contact binary: (126719) 2002 CC249

Authors: Audrey Thirouin, Scott S. Sheppard

Abstract: Images of the Kuiper belt object (126719) 2002 CC249 obtained in 2016 and 2017 using the 6.5m Magellan-Baade Telescope and the 4.3m Discovery Channel Telescope are presented. A lightcurve with a periodicity of 11.87+/-0.01 h and a peak-to-peak amplitude of 0.79+/-0.04 mag is reported. This high amplitude double-peaked lightcurve can be due to a single elongated body, but it is best explained by a… ▽ More Images of the Kuiper belt object (126719) 2002 CC249 obtained in 2016 and 2017 using the 6.5m Magellan-Baade Telescope and the 4.3m Discovery Channel Telescope are presented. A lightcurve with a periodicity of 11.87+/-0.01 h and a peak-to-peak amplitude of 0.79+/-0.04 mag is reported. This high amplitude double-peaked lightcurve can be due to a single elongated body, but it is best explained by a contact binary system from its U-/V-shaped lightcurve. We present a simple full-width-at-half-maximum (FWHM) test that can be used to determine if an object is likely a contact binary or an elongated object based on its lightcurve. Considering that 2002 CC249 is in hydrostatic equilibrium, a system with a mass ratio qmin=0.6, and a density ρmin=1gcc, or less plausible a system with qmax=1, and ρmax=5gcc can interpret the lightcurve. Assuming a single Jacobi ellipsoid in hydrostatic equilibrium, and an equatorial view, we estimate ρ= 0.34gcc, and a/b=2.07. Finally, we report a new color study showing that 2002 CC249 displays an ultra red surface characteristic of a dynamically Cold Classical trans-Neptunian object. △ Less

Submitted 28 October, 2017; originally announced October 2017.

Comments: In press, The Astronomical Journal

2004 TT357: A potential contact binary in the Trans-Neptunian belt

Authors: Audrey Thirouin, Scott S. Sheppard, Keith S. Noll

Abstract: We report photometric observations of the trans-Neptunian object 2004~TT$_{357}$ obtained in 2015 and 2017 using the 4.3~m Lowell's Discovery Channel Telescope. We derive a rotational period of 7.79$\pm$0.01~h and a peak-to-peak lightcurve amplitude of 0.76$\pm$0.03~mag. 2004 TT$_{357}$ displays a large variability that can be explained by a very elongated single object or can be due to a contact/… ▽ More We report photometric observations of the trans-Neptunian object 2004~TT$_{357}$ obtained in 2015 and 2017 using the 4.3~m Lowell's Discovery Channel Telescope. We derive a rotational period of 7.79$\pm$0.01~h and a peak-to-peak lightcurve amplitude of 0.76$\pm$0.03~mag. 2004 TT$_{357}$ displays a large variability that can be explained by a very elongated single object or can be due to a contact/close binary. The most likely scenario is that 2004 TT$_{357}$ is a contact binary. If it is in hydrostatic equilibrium, we find that the lightcurve can be explained by a system with a mass ratio q$_{min}$=0.45$\pm$0.05, and a density of $ρ_{min}$=2g cm$^{-3}$, or less likely a system with q$_{max}$=0.8$\pm$0.05, and $ρ_{max}$=5g cm$^{-3}$. Considering a single triaxial ellipsoid in hydrostatic equilibrium, we derive a lower limit to the density of 0.78g cm$^{-3}$, and an elongation (a/b) of 2.01 assuming an equatorial view. From Hubble Space Telescope data, we report no resolved companion orbiting 2004 TT$_{357}$. Despite an expected high fraction of contact binaries in the trans-Neptunian belt, 2001 QG$_{298}$ is the unique confirmed contact binary in the trans-Neptunian belt, and 2004 TT$_{357}$ is only the second candidate to this class of systems, with 2003 SQ$_{317}$. △ Less

Submitted 31 July, 2017; originally announced July 2017.

Comments: In Press, ApJ

All planetesimals born near the Kuiper Belt formed as binaries

Authors: Wesley C. Fraser, Michele t. Bannister, Rosemary E. Pike, Michael Marsset, Megan E. Schwamb, J. J. Kavelaars, Pedro Lacerda, David Nesvornyy, Kathryn Volk, audrey Delsanti, Susan Benecchi, Matthew J. Lehner, Keith Noll, Brett Gladman, Jean-Marc Petit, Stephen Gwyn, Ying-tung Chen, Shiang-Yu Wang, Mike Alexandersen, Todd Burdullis, Scott Sheppard, Chad Trujillo

Abstract: The cold classical Kuiper belt objects have low inclinations and eccentricities and are the only Kuiper belt population suspected to have formed in situ. Compared with the dynamically excited populations, which exhibit a broad range of colours and a low binary fraction of ~10% cold classical Kuiper belt objects typically have red optical colours with ~30% of the population found in binary pairs; t… ▽ More The cold classical Kuiper belt objects have low inclinations and eccentricities and are the only Kuiper belt population suspected to have formed in situ. Compared with the dynamically excited populations, which exhibit a broad range of colours and a low binary fraction of ~10% cold classical Kuiper belt objects typically have red optical colours with ~30% of the population found in binary pairs; the origin of these differences remains unclear. We report the detection of a population of blue-coloured, tenuously bound binaries residing among the cold classical Kuiper belt objects. Here we show that widely separated binaries could have survived push-out into the cold classical region during the early phases of Neptune's migration. The blue binaries may be contaminants, originating at ~38 au, and could provide a unique probe of the formative conditions in a region now nearly devoid of objects. The idea that the blue objects, which are predominantly binary, are the products of push-out requires that the planetesimals formed entirely as multiples. Plausible formation routes include planetesimal formation via pebble accretion and subsequent binary production through dynamic friction and binary formation during the collapse of a cloud of solids. △ Less

Submitted 1 May, 2017; originally announced May 2017.

Comments: 7 Figures, 3 tables, accepted to Nature Astronomy. Main manuscript and supplement available at http://www.nature.com/articles/s41550-017-0088