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Fundamentals of interior modelling and challenges in the interpretation of observed rocky exoplanets
Authors:
Philipp Baumeister,
Francesca Miozzi,
Claire Marie Guimond,
Marie-Luise Steinmeyer,
Caroline Dorn,
Shun-Ichiro Karato,
Emeline Bolmont,
Alexandre Revol,
Alexander Thamm,
Lena Noack
Abstract:
Most our knowledge about rocky exoplanets is based on their measure of mass and radius. These two parameters are routinely measured and are used to categorise different populations of observed exoplanets. They are also tightly linked to the planet's properties, in particular those of the interior. As such they offer the unique opportunity to interpret the observations and potentially infer the pla…
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Most our knowledge about rocky exoplanets is based on their measure of mass and radius. These two parameters are routinely measured and are used to categorise different populations of observed exoplanets. They are also tightly linked to the planet's properties, in particular those of the interior. As such they offer the unique opportunity to interpret the observations and potentially infer the planet's chemistry and structure. Required for the interpretation are models of planetary interiors, calculated a priori, constrained using other available data, and based on the physiochemical properties of mineralogical phases. This article offers an overview of the current knowledge about exoplanet interiors, the fundamental aspects and tools for interior modelling and how to improve the contraints on the models, along with a discussion on the sources of uncertainty. The origin and fate of volatiles, and their role in planetary evolution is discussed. The chemistry and structure of planetary interiors have a pivotal role in the thermal evolution of planets and the development of large scale properties that might become observables with future space missions and ground-based surveys. As such, having reliable and well constrained interior models is of the utmost importance for the advancement of the field.
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Submitted 13 November, 2025;
originally announced November 2025.
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A diamond anvil microassembly for Joule heating and electrical measurements up to 150 GPa and 4000 K
Authors:
Zachary M. Geballe,
Suzy M. Vitale,
Jing Yang,
Francesca Miozzi,
Vasilije V. Dobrosavljevic,
Michael J. Walter
Abstract:
When diamond anvil cell (DAC) sample chambers are outfitted with both thermal insulation and electrodes, two cutting-edge experimental methods are enabled: Joule heating with spectroradiometric temperature measurement, and electrical resistance measurements of samples heated to thousands of kelvin. The accuracy of temperature and resistance measurements, however, often suffers from poor control of…
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When diamond anvil cell (DAC) sample chambers are outfitted with both thermal insulation and electrodes, two cutting-edge experimental methods are enabled: Joule heating with spectroradiometric temperature measurement, and electrical resistance measurements of samples heated to thousands of kelvin. The accuracy of temperature and resistance measurements, however, often suffers from poor control of the shape and location of the sample, electrodes, and thermal insulation. Here, we present a recipe for the reproducible and precise fabrication of DAC sample, electrodes, and thermal insulation using a three-layer microassembly. The microassembly contains two potassium chloride thermal insulation layers, four electrical leads, a sample, and a buttressing layer made of polycrystalline alumina. The sample, innermost electrodes, and buttress layer are fabricated by focused-ion-beam milling. Three iron samples are presented as proof of concept. Each is successfully compressed and pulsed Joule heated while maintaining a four-point probe configuration. The highest pressure-temperature condition achieved is $\sim 150$ GPa and $\sim 4000$ K.
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Submitted 27 October, 2023;
originally announced October 2023.
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Spectroradiometry with sub-microsecond time resolution using multianode photomultiplier tube assemblies
Authors:
Zachary M. Geballe,
Francesca Miozzi,
Chris F. Anto,
Javier Rojas,
Jing Yang,
Michael J. Walter
Abstract:
Accurate and precise measurements of spectroradiometric temperature are crucial for many high pressure experiments that use diamond anvil cells or shock waves. In experiments with sub-millisecond timescales, specialized detectors such as streak cameras or photomultiplier tubes are required to measure temperature. High accuracy and precision are difficult to attain, especially at temperatures below…
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Accurate and precise measurements of spectroradiometric temperature are crucial for many high pressure experiments that use diamond anvil cells or shock waves. In experiments with sub-millisecond timescales, specialized detectors such as streak cameras or photomultiplier tubes are required to measure temperature. High accuracy and precision are difficult to attain, especially at temperatures below 3000 K. Here we present a new spectroradiometry system based on multianode photomultiplier tube technology and passive readout circuitry that yields a 0.24 $μ$s rise-time for each channel. Temperature is measured using five color spectroradiometry. During high pressure pulsed Joule heating experiments in a diamond anvil cell, we document measurement precision to be $\pm 30$ K at temperatures as low as 2000 K during single-shot heating experiments with $0.6$ $μ$s time-resolution. Ambient pressure melting tests using pulsed Joule heating indicate that the accuracy is $\pm 80$ K in the temperature range 1800-2700 K.
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Submitted 25 October, 2023;
originally announced October 2023.
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Ultra-high pressure disordered eight-coordinated phase of Mg$_2$GeO$_4$: Analogue for super-Earth mantles
Authors:
Rajkrishna Dutta,
Sally J. Tracy,
Ronald E. Cohen,
Francesca Miozzi,
Kai Luo,
Jing Yang,
Pamela C. Burnley,
Dean Smith,
Yue Meng,
Stella Chariton,
Vitali B. Prakapenka,
Thomas S. Duffy
Abstract:
Mg2GeO4 is an analogue for the ultra-high pressure behavior of Mg2SiO4, so we have investigated magnesium germanate to 275 GPa and over 2000 K using a laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction and density functional theory (DFT) computations. The experimental results are consistent with a novel phase with disordered Mg and Ge, in which germanium adopts eig…
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Mg2GeO4 is an analogue for the ultra-high pressure behavior of Mg2SiO4, so we have investigated magnesium germanate to 275 GPa and over 2000 K using a laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction and density functional theory (DFT) computations. The experimental results are consistent with a novel phase with disordered Mg and Ge, in which germanium adopts eight-fold coordination with oxygen: the cubic Th3P4- type structure. Simulations using the special quasirandom structure (SQS) method suggest partial order in the tetragonal I-42d structure, indistinguishable from I-43d Th3P4 in our experiments. These structures have not been reported before in any oxide. If applicable to silicates, the formation of this highly coordinated and intrinsically disordered phase would have important implications for the interior mineralogy of large, rocky extrasolar planets.
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Submitted 20 August, 2021; v1 submitted 1 January, 2021;
originally announced January 2021.