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Development of an X-ray polarimeter at the SOLEIL Synchrotron
Authors:
L. Manzanillas,
J. M. Ablett,
M. Choukroun,
F. J. Iguaz,
J. P. Rueff
Abstract:
Synchrotron radiation facilities provide highly polarized X-ray beams across a wide energy range. However, the exact type and degree of polarization varies according to the beamline and experimental setup. To accurately determine the angle and degree of linear polarization, a portable X-ray polarimeter has been developed. This setup consists of a Silicon Drift Detector that rotates around a target…
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Synchrotron radiation facilities provide highly polarized X-ray beams across a wide energy range. However, the exact type and degree of polarization varies according to the beamline and experimental setup. To accurately determine the angle and degree of linear polarization, a portable X-ray polarimeter has been developed. This setup consists of a Silicon Drift Detector that rotates around a target made of high-density polyethylene. The imprint generated in the angular distribution of scattered photons at a 90-degree angle from the target has been exploited to determine the beam polarization. Measurements were conducted at the GALAXIES beamline of the SOLEIL Synchrotron. The expected angular distribution of the scattered photons for a given beam polarization was obtained through simulations using the Geant4 simulation toolkit. An excellent agreement between simulations and the collected data has been obtained, validating the setup and enabling a precise determination of the beam polarization.
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Submitted 12 September, 2023; v1 submitted 11 September, 2023;
originally announced September 2023.
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Experimental Characterization of the Pyridine:Acetylene Co-crystal and Implications for Titan's Surface
Authors:
Ellen C. Czaplinski,
Tuan H. Vu,
Morgan L. Cable,
Mathieu Choukroun,
Michael J. Malaska,
Robert Hodyss
Abstract:
Titan, Saturn's largest moon, has a plethora of organic compounds in the atmosphere and on the surface that interact with each other. Cryominerals such as co-crystals may influence the geologic processes and chemical composition of Titan's surface, which in turn informs our understanding of how Titan may have evolved, how the surface is continuing to change, as well as the extent of Titan's habita…
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Titan, Saturn's largest moon, has a plethora of organic compounds in the atmosphere and on the surface that interact with each other. Cryominerals such as co-crystals may influence the geologic processes and chemical composition of Titan's surface, which in turn informs our understanding of how Titan may have evolved, how the surface is continuing to change, as well as the extent of Titan's habitability. Previous work has shown that a pyridine:acetylene (1:1) co-crystal forms under specific temperatures and experimental conditions; however, this has not yet been demonstrated under Titan-relevant conditions. Our work here demonstrates that the pyridine:acetylene co-crystal is stable from 90 K, Titan's average surface temperature, up to 180 K under an atmosphere of N2. In particular, the co-crystal forms via liquid-solid interactions within minutes upon mixing of the constituents at 150 K, as evidenced by distinct, new Raman bands and band shifts. XRD results indicate moderate anisotropic thermal expansion (about 0.5% - 1.1%) along the three principal axes between 90-150 K. Additionally, the co-crystal is detectable after being exposed to liquid ethane, implying stability in a residual ethane "wetting" scenario on Titan. These results suggest that the pyridine:acetylene co-crystal could form in specific geologic contexts on Titan that allow for warm environments in which liquid pyridine could persist, and as such, this cryomineral may preserve evidence of impact, cryovolcanism, or subsurface transport in surface materials.
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Submitted 28 February, 2023;
originally announced February 2023.
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CO2-driven surface changes in the Hapi region on Comet 67P/Churyumov-Gerasimenko
Authors:
Björn J. R. Davidsson,
F. Peter Schloerb,
Sonia Fornasier,
Nilda Oklay,
Pedro J. Gutiérrez,
Bonnie J. Buratti,
Artur B. Chmielewski,
Samuel Gulkis,
Mark D. Hofstadter,
H. Uwe Keller,
Holger Sierks,
Carsten Güttler,
Michael Küppers,
Hans Rickman,
Mathieu Choukroun,
Seungwon Lee,
Emmanuel Lellouch,
Anthony Lethuillier,
Vania Da Deppo,
Olivier Groussin,
Ekkehard Kührt,
Nicolas Thomas,
Cecilia Tubiana,
M. Ramy El-Maarry,
Fiorangela La Forgia
, et al. (2 additional authors not shown)
Abstract:
Between 2014 December 31 and 2015 March 17, the OSIRIS cameras on Rosetta documented the growth of a 140m wide and 0.5m deep depression in the Hapi region on Comet 67P/Churyumov-Gerasimenko. This shallow pit is one of several that later formed elsewhere on the comet, all in smooth terrain that primarily is the result of airfall of coma particles. We have compiled observations of this region in Hap…
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Between 2014 December 31 and 2015 March 17, the OSIRIS cameras on Rosetta documented the growth of a 140m wide and 0.5m deep depression in the Hapi region on Comet 67P/Churyumov-Gerasimenko. This shallow pit is one of several that later formed elsewhere on the comet, all in smooth terrain that primarily is the result of airfall of coma particles. We have compiled observations of this region in Hapi by the microwave instrument MIRO on Rosetta, acquired during October and November 2014. We use thermophysical and radiative transfer models in order to reproduce the MIRO observations. This allows us to place constraints on the thermal inertia, diffusivity, chemical composition, stratification, extinction coefficients, and scattering properties of the surface material, and how they evolved during the months prior to pit formation. The results are placed in context through long-term comet nucleus evolution modelling. We propose that: 1) MIRO observes signatures that are consistent with a solid-state greenhouse effect in airfall material; 2) CO2 ice is sufficiently close to the surface to have a measurable effect on MIRO antenna temperatures, and likely is responsible for the pit formation in Hapi observed by OSIRIS; 3) the pressure at the CO2 sublimation front is sufficiently strong to expel dust and water ice outwards, and to compress comet material inwards, thereby causing the near-surface compaction observed by CONSERT, SESAME, and groundbased radar, manifested as the "consolidated terrain" texture observed by OSIRIS.
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Submitted 14 October, 2022;
originally announced October 2022.
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Operations for Autonomous Spacecraft
Authors:
Rebecca Castano,
Tiago Vaquero,
Federico Rossi,
Vandi Verma,
Ellen Van Wyk,
Dan Allard,
Bennett Huffmann,
Erin M. Murphy,
Nihal Dhamani,
Robert A. Hewitt,
Scott Davidoff,
Rashied Amini,
Anthony Barrett,
Julie Castillo-Rogez,
Steve A. Chien,
Mathieu Choukroun,
Alain Dadaian,
Raymond Francis,
Benjamin Gorr,
Mark Hofstadter,
Mitch Ingham,
Cristina Sorice,
Iain Tierney
Abstract:
Onboard autonomy technologies such as planning and scheduling, identification of scientific targets, and content-based data summarization, will lead to exciting new space science missions. However, the challenge of operating missions with such onboard autonomous capabilities has not been studied to a level of detail sufficient for consideration in mission concepts. These autonomy capabilities will…
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Onboard autonomy technologies such as planning and scheduling, identification of scientific targets, and content-based data summarization, will lead to exciting new space science missions. However, the challenge of operating missions with such onboard autonomous capabilities has not been studied to a level of detail sufficient for consideration in mission concepts. These autonomy capabilities will require changes to current operations processes, practices, and tools. We have developed a case study to assess the changes needed to enable operators and scientists to operate an autonomous spacecraft by facilitating a common model between the ground personnel and the onboard algorithms. We assess the new operations tools and workflows necessary to enable operators and scientists to convey their desired intent to the spacecraft, and to be able to reconstruct and explain the decisions made onboard and the state of the spacecraft. Mock-ups of these tools were used in a user study to understand the effectiveness of the processes and tools in enabling a shared framework of understanding, and in the ability of the operators and scientists to effectively achieve mission science objectives.
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Submitted 21 November, 2021;
originally announced November 2021.
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Vertical compositional variations of liquid hydrocarbons in Titan's alkanofers
Authors:
Daniel Cordier,
David A. Bonhommeau,
Tuan H. Vu,
Mathieu Choukroun,
Fernando Garcia-Sanchez
Abstract:
According to clues left by the Cassini mission, Titan, one of the two Solar System bodies with a hydrologic cycle, may harbor liquid hydrocarbon-based analogs of our terrestrial aquifers, referred to as "alkanofers". On the Earth, petroleum and natural gas reservoirs show a vertical gradient in chemical composition, established over geological timescales. In this work, we aim to investigate the co…
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According to clues left by the Cassini mission, Titan, one of the two Solar System bodies with a hydrologic cycle, may harbor liquid hydrocarbon-based analogs of our terrestrial aquifers, referred to as "alkanofers". On the Earth, petroleum and natural gas reservoirs show a vertical gradient in chemical composition, established over geological timescales. In this work, we aim to investigate the conditions under which Titan's processes could lead to similar situations. We built numerical models including barodiffusion and thermodiffusion (Soret's effect) in N_2+CH_4+C_2H_6 liquid mixtures, which are relevant for Titan's possible alkanofers. Our main assumption is the existence of reservoirs of liquids trapped in a porous matrix with low permeability. Due to the small size of the molecule, nitrogen seems to be more sensitive to gravity than ethane, even if the latter has a slightly larger mass. This behavior, noticed for an isothermal crust, is reinforced by the presence of a geothermal gradient. Vertical composition gradients, formed over timescales of between a fraction of a mega-year to several tens of mega-years, are not influenced by molecular diffusion coefficients. We find that ethane does not accumulate at the bottom of the alkanofers under diffusion, leaving the question of why ethane is not observed on Titan's surface unresolved. If the alkanofer liquid was in contact with water-ice, we checked that N_2 did not, in general, impede the clathration of C_2H_6, except in some layers. Interestingly, we found that noble gases could easily accumulate at the bottom of an alkanofer.
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Submitted 13 July, 2021;
originally announced July 2021.
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The Case for Non-Cryogenic Comet Nucleus Sample Return
Authors:
Keiko Nakamura-Messenger,
Alexander G. Hayes,
Scott Sandford,
Carol Raymond,
Steven W. Squyres,
Larry R. Nittler,
Samuel Birch,
Denis Bodewits,
Nancy Chabot,
Meenakshi Wadhwa,
Mathieu Choukroun,
Simon J. Clemett,
Maitrayee Bose,
Neil Dello Russo,
Jason P. Dworkin,
Jamie E. Elsila,
Kenton Fisher,
Perry Gerakines,
Daniel P. Glavin,
Julie Mitchell,
Michael Mumma,
Ann. N. Nguyen,
Lisa Pace,
Jason Soderblom,
Jessica M. Sunshine
Abstract:
Comets hold answers to mysteries of the Solar System by recording presolar history, the initial states of planet formation and prebiotic organics and volatiles to the early Earth. Analysis of returned samples from a comet nucleus will provide unparalleled knowledge about the Solar System starting materials and how they came together to form planets and give rise to life:
1. How did comets form?…
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Comets hold answers to mysteries of the Solar System by recording presolar history, the initial states of planet formation and prebiotic organics and volatiles to the early Earth. Analysis of returned samples from a comet nucleus will provide unparalleled knowledge about the Solar System starting materials and how they came together to form planets and give rise to life:
1. How did comets form?
2. Is comet material primordial, or has it undergone a complex alteration history?
3. Does aqueous alteration occur in comets?
4. What is the composition of cometary organics?
5. Did comets supply a substantial fraction of Earth's volatiles?
6. Did cometary organics contribute to the homochirality in life on Earth?
7. How do complex organic molecules form and evolve in interstellar, nebular, and planetary environments?
8. What can comets tell us about the mixing of materials in the protosolar nebula?
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Submitted 29 September, 2020;
originally announced September 2020.
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The Science Case for a Titan Flagship-class Orbiter with Probes
Authors:
Conor A. Nixon,
James Abshire,
Andrew Ashton,
Jason W. Barnes,
Nathalie Carrasco,
Mathieu Choukroun,
Athena Coustenis,
Louis-Alexandre Couston,
Niklas Edberg,
Alexander Gagnon,
Jason D. Hofgartner,
Luciano Iess,
Stéphane Le Mouélic,
Rosaly Lopes,
Juan Lora,
Ralph D. Lorenz,
Adrienn Luspay-Kuti,
Michael Malaska,
Kathleen Mandt,
Marco Mastrogiuseppe,
Erwan Mazarico,
Marc Neveu,
Taylor Perron,
Jani Radebaugh,
Sébastien Rodriguez
, et al. (14 additional authors not shown)
Abstract:
We outline a flagship-class mission concept focused on studying Titan as a global system, with particular emphasis on the polar regions. Investigating Titan from the unique standpoint of a polar orbit would enable comprehensive global maps to uncover the physics and chemistry of the atmosphere, and the topography and geophysical environment of the surface and subsurface. The mission includes two k…
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We outline a flagship-class mission concept focused on studying Titan as a global system, with particular emphasis on the polar regions. Investigating Titan from the unique standpoint of a polar orbit would enable comprehensive global maps to uncover the physics and chemistry of the atmosphere, and the topography and geophysical environment of the surface and subsurface. The mission includes two key elements: (1) an orbiter spacecraft, which also acts as a data relay, and (2) one or more small probes to directly investigate Titan's seas and make the first direct measurements of their liquid composition and physical environment. The orbiter would carry a sophisticated remote sensing payload, including a novel topographic lidar, a long-wavelength surface-penetrating radar, a sub-millimeter sounder for winds and for mesospheric/thermospheric composition, and a camera and near-infrared spectrometer. An instrument suite to analyze particles and fields would include a mass spectrometer to focus on the interactions between Titan's escaping upper atmosphere and the solar wind and Saturnian magnetosphere. The orbiter would enter a stable polar orbit around 1500 to 1800 km, from which vantage point it would make global maps of the atmosphere and surface. One or more probes, released from the orbiter, would investigate Titan's seas in situ, including possible differences in composition between higher and lower latitude seas, as well as the atmosphere during the parachute descent. The number of probes, as well as the instrument complement on the orbiter and probe, remain to be finalized during a mission study that we recommend to NASA as part of the NRC Decadal Survey for Planetary Science now underway, with the goal of an overall mission cost in the "small flagship" category of ~$2 bn. International partnerships, similar to Cassini-Huygens, may also be included for consideration.
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Submitted 13 August, 2020;
originally announced August 2020.
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AMBITION -- Comet Nucleus Cryogenic Sample Return (White paper for ESA's Voyage 2050 programme)
Authors:
D. Bockelée-Morvan,
G. Filacchione,
K. Altwegg,
E. Bianchi,
M. Bizzarro,
J. Blum,
L. Bonal,
F. Capaccioni,
C. Codella,
M. Choukroun,
H. Cottin,
B. Davidsson,
M. C. De Sanctis,
M. Drozdovskaya,
C. Engrand,
M. Galand,
C. Güttler,
P. Henri,
A. Herique,
S. Ivanoski,
R. Kokotanekova,
A. -C. Levasseur-Regourd,
K. E. Miller,
A. Rotundi,
M. Schönbächler
, et al. (5 additional authors not shown)
Abstract:
This white paper proposes that AMBITION, a Comet Nucleus Sample Return mission, be a cornerstone of ESA's Voyage 2050 programme. We summarise some of the most important questions still open in cometary science after the successes of the Rosetta mission, many of which require sample analysis using techniques that are only possible in laboratories on Earth. We then summarise measurements, instrument…
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This white paper proposes that AMBITION, a Comet Nucleus Sample Return mission, be a cornerstone of ESA's Voyage 2050 programme. We summarise some of the most important questions still open in cometary science after the successes of the Rosetta mission, many of which require sample analysis using techniques that are only possible in laboratories on Earth. We then summarise measurements, instrumentation and mission scenarios that can address these questions, with a recommendation that ESA select an ambitious cryogenic sample return mission. Rendezvous missions to Main Belt comets and Centaurs are compelling cases for M-class missions, expanding our knowledge by exploring new classes of comets. AMBITION would engage a wide community, drawing expertise from a vast range of disciplines within planetary science and astrophysics. With AMBITION, Europe will continue its leadership in the exploration of the most primitive Solar System bodies.
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Submitted 25 July, 2019;
originally announced July 2019.
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No compelling evidence for clathrate hydrate formation under interstellar medium conditions over laboratory timescales
Authors:
Mathieu Choukroun,
Tuan H. Vu,
Edith C. Fayolle
Abstract:
A recent article reported experimental observations of methane and CO2 clathrate formation at conditions similar to the interstellar medium (ISM), namely 10-30 K and 10-10 mbar. The authors conducted time-dependent reflection-absorption infrared spectroscopy (RAIRS) of vapor-deposited H2O:CH4 and H2O:CO2 mixtures and interpreted new blue and red -shifted peaks from those of trapped CH4 and CO2 in…
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A recent article reported experimental observations of methane and CO2 clathrate formation at conditions similar to the interstellar medium (ISM), namely 10-30 K and 10-10 mbar. The authors conducted time-dependent reflection-absorption infrared spectroscopy (RAIRS) of vapor-deposited H2O:CH4 and H2O:CO2 mixtures and interpreted new blue and red -shifted peaks from those of trapped CH4 and CO2 in amorphous ice, respectively, as indicative of clathrate formation. In this Letter to the Editor, we point out potential pitfalls and caution against the implications drawn for the ISM.
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Submitted 8 July, 2019; v1 submitted 22 May, 2019;
originally announced May 2019.
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The microstructural evolution of water ice in the solar system through sintering
Authors:
Jamie L. Molaro,
Mathieu Choukroun,
Cynthia B. Phillips,
Eli S. Phelps,
Robert Hodyss,
Karl L. Mitchell,
Juan M. Lora,
Gareth Meirion-Griffith
Abstract:
Ice sintering is a form of metamorphism that drives the microstructural evolution of an aggregate of grains through surface and volume diffusion. This leads to an increase in the grain-to-grain contact area ("neck") and density of the aggregate over time, resulting in the evolution of its strength, porosity, thermal conductivity, and other properties. This process plays an important role in the ev…
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Ice sintering is a form of metamorphism that drives the microstructural evolution of an aggregate of grains through surface and volume diffusion. This leads to an increase in the grain-to-grain contact area ("neck") and density of the aggregate over time, resulting in the evolution of its strength, porosity, thermal conductivity, and other properties. This process plays an important role in the evolution of icy planetary surfaces, though its rate and nature are not well constrained. In this study, we explore the model of Swinkels and Ashby (1981), and assess the extent to which it can be used to quantify sintering timescales for water ice. We compare predicted neck growth rates to new and historical observations of ice sintering, and find agreement to some studies at the order of magnitude level. First-order estimates of neck growth timescales on planetary surfaces show that ice may undergo significant modification over geologic timescales, even in the outer solar system. Densification occurs over much longer timescales, suggesting some surfaces may develop cohesive, but porous, crusts. Sintering rates are extremely sensitive to temperature and grain size, occurring faster in warmer aggregates of smaller grains. This suggests that the microstructural evolution of ices may vary not only throughout the solar system, but also spatially across the surface and in the near-surface of a given body. Our experimental observations of complex grain growth and mass redistribution in ice aggregates point to components of the model that may benefit from improvement, and areas where additional laboratory studies are needed.
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Submitted 14 January, 2019;
originally announced January 2019.
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The Rosetta mission orbiter Science overview the comet phase
Authors:
M. G. G. T. Taylor,
N. Altobelli,
B. J. Buratti,
M. Choukroun
Abstract:
The International Rosetta Mission was launched in 2004 and consists of the orbiter spacecraft Rosetta and the lander Philae. The aim of the mission is to map the comet 67P Churyumov Gerasimenko by remote sensing, to examine its environment insitu and its evolution in the inner solar system.Rosetta was the first spacecraft to rendezvous and orbit a comet, accompanying it as it passes through the in…
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The International Rosetta Mission was launched in 2004 and consists of the orbiter spacecraft Rosetta and the lander Philae. The aim of the mission is to map the comet 67P Churyumov Gerasimenko by remote sensing, to examine its environment insitu and its evolution in the inner solar system.Rosetta was the first spacecraft to rendezvous and orbit a comet, accompanying it as it passes through the inner solar system, and to deploy a lander, Philae and perform in situ science on the comet surface. The primary goals of the mission were to: characterize the comets nucleus; examine the chemical, mineralogical and isotopic composition of volatiles and refractories; examine the physical properties and interrelation of volatiles and refractories in a cometary nucleus; study the development of cometary activity and the processes in the surface layer of the nucleus and in the coma; detail the origin of comets, the relationship between cometary and interstellar material and the implications for the origin of the solar system; characterize asteroids, 2867 Steins and 21 Lutetia. This paper presents a summary of mission operations and science, focusing on the Rosetta orbiter component of the mission during its comet phase, from early 2014 up to September 2016.
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Submitted 30 March, 2017;
originally announced March 2017.
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Equilibrium composition between liquid and clathrate reservoirs on Titan
Authors:
Olivier Mousis,
Mathieu Choukroun,
Jonathan I. Lunine,
Christophe Sotin
Abstract:
Hundreds of lakes and a few seas of liquid hydrocarbons have been observed by the Cassini spacecraft to cover the polar regions of Titan. A significant fraction of these lakes or seas could possibly be interconnected with subsurface liquid reservoirs of alkanes. In this paper, we investigate the interplay that would happen between a reservoir of liquid hydrocarbons located in Titan's subsurface an…
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Hundreds of lakes and a few seas of liquid hydrocarbons have been observed by the Cassini spacecraft to cover the polar regions of Titan. A significant fraction of these lakes or seas could possibly be interconnected with subsurface liquid reservoirs of alkanes. In this paper, we investigate the interplay that would happen between a reservoir of liquid hydrocarbons located in Titan's subsurface and a hypothetical clathrate reservoir that progressively forms if the liquid mixture diffuses throughout a preexisting porous icy layer. To do so, we use a statistical-thermodynamic model in order to compute the composition of the clathrate reservoir that forms as a result of the progressive entrapping of the liquid mixture. This study shows that clathrate formation strongly fractionates the molecules between the liquid and the solid phases. Depending on whether the structure I or structure II clathrate forms, the present model predicts that the liquid reservoirs would be mainly composed of either propane or ethane, respectively. The other molecules present in the liquid are trapped in clathrates. Any river or lake emanating from subsurface liquid reservoirs that significantly interacted with clathrate reservoirs should present such composition. On the other hand, lakes and rivers sourced by precipitation should contain higher fractions of methane and nitrogen, as well as minor traces of argon and carbon monoxide.
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Submitted 26 May, 2014;
originally announced May 2014.
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A Hot Gap Around Jupiter's Orbit in the Solar Nebula
Authors:
N. J. Turner,
M. Choukroun,
J. Castillo-Rogez,
G. Bryden
Abstract:
The Sun was an order of magnitude more luminous during the first few hundred thousand years of its existence, due in part to the gravitational energy released by material accreting from the Solar nebula. If Jupiter was already near its present mass, the planet's tides opened an optically-thin gap in the nebula. We show using Monte Carlo radiative transfer calculations that sunlight absorbed by the…
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The Sun was an order of magnitude more luminous during the first few hundred thousand years of its existence, due in part to the gravitational energy released by material accreting from the Solar nebula. If Jupiter was already near its present mass, the planet's tides opened an optically-thin gap in the nebula. We show using Monte Carlo radiative transfer calculations that sunlight absorbed by the nebula and re-radiated into the gap raised temperatures well above the sublimation threshold for water ice, with potentially drastic consequences for the icy bodies in Jupiter's feeding zone. Bodies up to a meter in size were vaporized within a single orbit if the planet was near its present location during this early epoch. Dust particles lost their ice mantles, and planetesimals were partially to fully devolatilized, depending on their size. Scenarios in which Jupiter formed promptly, such as those involving a gravitational instability of the massive early nebula, must cope with the high temperatures. Enriching Jupiter in the noble gases through delivery trapped in clathrate hydrates will be more difficult, but might be achieved by either forming the planet much further from the star, or capturing planetesimals at later epochs. The hot gap resulting from an early origin for Jupiter also would affect the surface compositions of any primordial Trojan asteroids.
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Submitted 9 January, 2012; v1 submitted 18 October, 2011;
originally announced October 2011.