arXiv subjects

Maggie A. Thompson

Publications and source records attributed to Maggie A. Thompson.

14 recordsLinked to original sources

arXiv2026

Magnesium silicate condensation in sub-Neptune envelopes: the fundamental link between chemistry, structure, and observables

Chemical interactions between the hydrogen-dominated envelopes and silicate-rich interiors of sub-Neptunes likely play a key role in shaping their atmospheric structure, mass-radius relations, and upper atmosphere composition. While atmospheric abundances and structure deeply influence each other, many existing models have either considered the effects of chemical interactions without the structural implications or have modeled the envelope structure using oversimplified chemical networks. In this work, we introduce Rocky Raccoon, a coupled chemical equilibrium-atmospheric structure model. This model incorporates Mg, Si, O, C, and H species and produces self-consistent atmospheric chemical and thermal profiles for sub-Neptune envelopes, treating multi-species condensation for the first time. We find that the condensation sequence of magnesium silicates above a magma ocean is determined by the basal magma composition. We show that these condensation sequences drive the upper atmospheric composition to two endmembers: high oxygen abundances in the underlying melt produce compositions rich in oxygen-bearing volatiles (sub-solar C/O) and higher mean molecular weight atmospheres with $μ\sim 4$ amu, while oxygen-poor melts produce lower mean molecular weight atmospheres dominated by methane and silane (super-solar C/O). The transition between the two regimes is abrupt and depends on melt properties like Mg/Si ratios and oxygen abundances. The different condensation sequences also lead to different thermal profiles, as deep convection is inhibited over different regions due to varying molecular weight gradients. Further experiments and simulations are key to resolving critical uncertainties in the condensation sequences and the corresponding significant impacts on sub-Neptune composition and thermal structure.

astro-ph.EP↗

arXiv2026

On the importance of laboratory experiments for interpreting exoplanet observations

With the advanced capabilities of ground- and space-based telescopes, exoplanet science is beginning to characterize the physics and chemistry of exoplanet atmospheres. However, interpreting exoplanet observations requires sophisticated modeling tools that rely on laboratory data to provide critical inputs and constraints. In preparation for the influx of observational data that the coming decades will bring, laboratory experiments that simulate the diverse conditions expected in exoplanet atmospheres, surfaces and interiors are vital to advancing models and thereby our understanding of these worlds. Here we discuss the key areas where laboratory experiments are providing fundamental data for exoplanet models, particularly for low-mass planets from rocky worlds to sub-Neptunes. First, we present a series of experiments to measure outgassing and volatile solubilities that are essential for establishing the connection between low-mass exoplanet interiors and their observable atmospheres. We then discuss additional laboratory techniques that can be used to understand the interior-atmosphere connection and simulate the high pressure-high temperature conditions of exoplanet interiors. Next, we summarize the experimental methods used to constrain the spectroscopic properties of atmospheric gases and aerosols along with their formation and reaction mechanisms. We also discuss how similar methods can be used to constrain exoplanet surface compositions, which is important for interpreting observations of atmosphere-less worlds. Finally, we conclude by presenting several examples of astrobiology experiments that constrain how life can modify the atmosphere and surface of rocky exoplanets. Together, these laboratory efforts are crucial to maximizing the scientific yield of exoplanet observations in the coming decades.

astro-ph.EP↗

arXiv2025

Diversity of low-mass planet atmospheres in the C-H-O-N-S-Cl system with interior dissolution, nonideality, and condensation: Application to TRAPPIST-1e and sub-Neptunes

A quantitative understanding of the nature and composition of low-mass rocky (exo)planet atmospheres during their evolution is needed to interpret observations. The magma ocean stage of terrestrial- and sub-Neptune planets permits mass exchange between their interiors and atmospheres, during which the mass and speciation of the atmosphere is dictated by the planet's volatile budget, chemical equilibria, and gas/fluid solubility in molten rock. As the atmosphere cools, it is modified by gas-phase reactions and condensation. We combine these processes into an open-source Python package built using JAX called Atmodeller, and perform calculations for planet sizes and conditions analogous to TRAPPIST-1e and K2-18b. For TRAPPIST-1e-like planets, our simulations indicate that CO-dominated atmospheres are prevalent during the magma ocean stage, which, upon isochemical cooling, predominantly evolve into CO2-rich atmospheres of a few hundred bar at 280 K. Around 40% of our simulations predict the coexistence of liquid water, graphite, alpha-sulfur, and ammonium chloride, which are key ingredients for surface habitability. For sub-Neptune gas dwarfs, pressures are sufficiently high (a few GPa) that gas fugacities deviate from ideality, thereby drastically enhancing solubilities. This buffers the total atmospheric pressure to lower values than for the ideal case. These effects conspire to produce CH4-rich sub-Neptune atmospheres for total pressures exceeding around 3.5 GPa, provided H/C is approximately 100x solar and fO2 moderately reducing (3 log10 units below the iron-wustite buffer). Otherwise, molecular hydrogen remains the predominant species at lower total pressures and/or higher H/C. For all planets at high temperature, solubility enriches C/H in the atmosphere relative to the initial composition.

astro-ph.EP↗

arXiv2025

Water solubility in silicate melts: The effects of melt composition under reducing conditions and implications for nebular ingassing on rocky planets

Rocky planet atmospheres form and evolve through interactions between the planet's surface and interior. If a growing rocky planet acquires enough mass prior to the dissipation of the nebular gas disk, it can gravitationally capture a `primary' atmosphere dominated by H2. At the same time, these young, rocky bodies are likely to have partial or global magma oceans as a result of the heat from accretion, core formation and radioactive decay of short-lived major element isotopes. During this magma ocean stage, the dissolution of volatile, life-essential elements, such as hydrogen in the form of water or H2, into the magma is critical in determining the extent to which a rocky planet can maintain these elements over time. However, our ability to quantify the amount of hydrogen dissolved in the magma oceans of rocky planets is limited by the lack of experimental constraints on H-bearing species' solubilities at relevant pressure and temperature conditions, including those expected for the early Earth. Here we experimentally determine the solubility of water in silicate melts of various compositions in the Ca-Mg-Al-Si-Fe-O system at a total pressure of 1 bar and temperatures from 1673-1823 K, synthesized in a H2-CO2 gas-mixing furnace. We use Bayesian parameter estimation to derive a robust water solubility law that includes the effects of melt composition and temperature. Using this solubility law, we estimate that ~100 ppm of hydrogen can dissolve into a 1 MEarth planet with a surface pressure of ~300 bars set by accretion of solar-like nebular gas. For rocky planets in general, ingassing of a primary atmosphere may be an important source and initial storage mechanism for hydrogen-bearing species in a planet's interior, provided it grew to a sufficient mass within the lifetime of the solar nebula.

astro-ph.EP↗

arXiv2023

Outgassing Composition of the Murchison Meteorite: Implications for Volatile Depletion of Planetesimals and Interior-atmosphere Connections for Terrestrial Exoplanets

Outgassing is a central process during the formation and evolution of terrestrial planets and their atmospheres both within and beyond the solar system. Although terrestrial planets' early atmospheres likely form via outgassing during planetary accretion, the connection between a planet's bulk composition and its initial atmospheric properties is not well understood. One way to inform this connection is to analyze the outgassing compositions of meteorites, and in particular carbonaceous chondrites, because they are some of the most volatile-rich, primitive materials (in terms of their bulk compositions) that are available for direct study. In addition, they may serve as compositional analogs for the building block materials of terrestrial planets in our solar system and around other Sun-like stars. This study builds upon previous outgassing experiments that monitored the abundances of volatile species (e.g., H2O, CO, and CO2) released from the Murchison meteorite. To gain a more complete understanding of Murchison's outgassing composition, we perform a series of heating experiments under atmospheric pressure (1 bar) and vacuum (1E-9 bar) conditions on samples of the Murchison meteorite and subsequent bulk element analysis to inform the outgassing trends of a suite of major elements in Murchison (e.g., Fe, Mg, Zn, and S). Under both pressure conditions, sulfur outgases significantly at the highest temperatures (800C - 1000C). For the samples heated under vacuum conditions, we also detect outgassing of zinc. Combined with prior outgassing experiments, this study provides important insights into the volatile depletion patterns of undifferentiated planetesimals and the early outgassing compositions of terrestrial exoplanets.

astro-ph.EP↗

arXiv2022

The Case and Context for Atmospheric Methane as an Exoplanet Biosignature

Methane has been proposed as an exoplanet biosignature. Imminent observations with the James Webb Space Telescope may enable methane detections on potentially habitable exoplanets, so it is essential to assess in what planetary contexts methane is a compelling biosignature. Methane's short photochemical lifetime in terrestrial planet atmospheres implies that abundant methane requires large replenishment fluxes. While methane can be produced by a variety of abiotic mechanisms such as outgassing, serpentinizing reactions, and impacts, we argue that, in contrast to an Earth-like biosphere, known abiotic processes cannot easily generate atmospheres rich in CH$_4$ and CO$_2$ with limited CO due to the strong redox disequilibrium between CH$_4$ and CO$_2$. Methane is thus more likely to be biogenic for planets with 1) a terrestrial bulk density, high mean-molecular-weight and anoxic atmosphere, and an old host star; 2) an abundance of CH$_4$ that implies surface fluxes exceeding what could be supplied by abiotic processes; and 3) atmospheric CO$_2$ with comparatively little CO.

astro-ph.EP↗

arXiv2021

Composition of Terrestrial Exoplanet Atmospheres from Meteorite Outgassing Experiments

Terrestrial exoplanets likely form initial atmospheres through outgassing during and after accretion, although there is currently no first-principles understanding of how to connect a planet's bulk composition to its early atmospheric properties. Important insights into this connection can be gained by assaying meteorites, representative samples of planetary building blocks. We perform laboratory outgassing experiments that use a mass spectrometer to measure the abundances of volatiles released when meteorite samples are heated to 1200 $^{\circ}$C. We find that outgassing from three carbonaceous chondrite samples consistently produce H$_2$O-rich (averaged ~66 %) atmospheres but with significant amounts of CO (~18 %) and CO$_2$ (~15 %) as well as smaller quantities of H$_2$ and H$_2$S (up to 1 %). These results provide experimental constraints on the initial chemical composition in theoretical models of terrestrial planet atmospheres, supplying abundances for principal gas species as a function of temperature.

astro-ph.EP↗

arXiv2020

The Importance of Prioritizing Exoplanet Experimental Facilities

Continuous improvements of observations and modeling efforts have led to tremendous strides in exoplanetary science. However, as instruments and techniques advance laboratory data becomes more important to interpret exoplanet observations and verify theoretical modeling. Though experimental studies are often deferred due to their high costs and long timelines, it is imperative that laboratory investigations are prioritized to ensure steady advances in the field of exoplanetary science. This White Paper discusses the importance of prioritizing exoplanetary laboratory efforts, and discusses several experimental facilities currently performing exoplanetary research.

astro-ph.IM↗

arXiv2019

Studying the Evolution of Warm Dust Encircling BD +20 307 Using SOFIA

The small class of known stars with unusually warm, dusty debris disks is a key sample to probe in order to understand cascade models and extreme collisions that likely lead to the final configurations of planetary systems. Because of its extreme dustiness and small radius, the disk of BD +20 307 has a short predicted collision time and is therefore an interesting target in which to look for changes in dust quantity and composition over time. To compare with previous ground and Spitzer Space Telescope data, SOFIA photometry and spectroscopy were obtained. The system's 8.8-12.5 $μ$m infrared emission increased by $10 \pm 2 \%$ over nine years between the SOFIA and earlier Spitzer measurements. In addition to an overall increase in infrared excess, there is a suggestion of a greater increase in flux at shorter wavelengths (less than 10.6 $μ$m) compared to longer wavelengths (greater than 10.6 $μ$m). Steady-state collisional cascade models cannot explain the increase in BD +20 307's disk flux over such short timescales. A catastrophic collision between planetary-scale bodies is still the most likely origin for the system's extreme dust; however, the cause for its recent variation requires further investigation.

astro-ph.EP↗

arXiv2018

Dynamical Masses of Eps Ind B and C: Two Massive Brown Dwarfs at the Edge of the Stellar-Substellar Boundary

We report individual dynamical masses for the brown dwarfs Epsilon Indi B and C, which have spectral types of T1.5 and T6, respectively, measured from astrometric orbit mapping. Our measurements are based on a joint analysis of astrometric data from the Carnegie Astrometric Planet Search and the Cerro Tololo Inter-American Observatory Parallax Investigation as well as archival high resolution imaging, and use a Markov Chain Monte Carlo method. We find dynamical masses of 75.0+-0.82 Mjup for the T1.5 B component and 70.1+-0.68 Mjup for the T6 C component. These masses are surprisingly high for substellar objects and challenge our understanding of substellar structure and evolution. We discuss several evolutionary scenarios proposed in the literature and find that while none of them can provide conclusive explanations for the high substellar masses, evolutionary models incorporating lower atmospheric opacities come closer to approximating our results. We discuss the details of our astrometric model, its algorithm implementation, and how we determine parameter values via Markov Chain Monte Carlo Bayesian inference.

astro-ph.SR↗

arXiv2013

Nearby M, L, and T Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)

In our effort to complete the census of low-mass stars and brown dwarfs in the immediate Solar Neighborhood, we present spectra, photometry, proper motions, and distance estimates for forty-two low-mass star and brown dwarf candidates discovered by the Wide-field Infrared Survey Explorer (WISE). We also present additional follow-up information on twelve candidates selected using WISE data but previously published elsewhere. The new discoveries include fifteen M dwarfs, seventeen L dwarfs, five T dwarfs, and five objects of other type. Among these discoveries is a newly identified "unusually red L dwarf" (WISE J223527.07+451140.9), four peculiar L dwarfs whose spectra are most readily explained as unresolved L+T binary systems, and a T9 dwarf (WISE J124309.61+844547.8). We also show that the recently discovered red L dwarf WISEP J004701.06+680352.1 (Gizis et al. 2012) may be a low-gravity object and hence young and potentially low mass (< 25 MJup).

astro-ph.SR↗

arXiv2013

A Study of the Diverse T Dwarf Population Revealed by WISE

We report the discovery of 87 new T dwarfs uncovered with the Wide-field Infrared Survey Explorer (WISE) and three brown dwarfs with extremely red near-infrared colors that exhibit characteristics of both L and T dwarfs. Two of the new T dwarfs are likely binaries with L7+/-1 primaries and mid-type T secondaries. In addition, our follow-up program has confirmed 10 previously identified T dwarfs and four photometrically-selected L and T dwarf candidates in the literature. This sample, along with the previous WISE discoveries, triples the number of known brown dwarfs with spectral types later than T5. Using the WISE All-Sky Source Catalog we present updated color-color and color-type diagrams for all the WISE-discovered T and Y dwarfs. Near-infrared spectra of the new discoveries are presented, along with spectral classifications. To accommodate later T dwarfs we have modified the integrated flux method of determining spectral indices to instead use the median flux. Furthermore, a newly defined J-narrow index differentiates the early-type Y dwarfs from late-type T dwarfs based on the J-band continuum slope. The K/J indices for this expanded sample show that 32% of late-type T dwarfs have suppressed K-band flux and are blue relative to the spectral standards, while only 11% are redder than the standards. Comparison of the Y/J and K/J index to models suggests diverse atmospheric conditions and supports the possible re-emergence of clouds after the L/T transition. We also discuss peculiar brown dwarfs and candidates that were found not to be substellar, including two Young Stellar Objects and two Active Galactic Nuclei. The coolest WISE-discovered brown dwarfs are the closest of their type and will remain the only sample of their kind for many years to come.

astro-ph.SR↗

arXiv2011

The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE)

We present ground-based spectroscopic verification of six Y dwarfs (see Cushing et al), eighty-nine T dwarfs, eight L dwarfs, and one M dwarf identified by the Wide-field Infrared Survey Explorer (WISE). Eighty of these are cold brown dwarfs with spectral types greater than or equal to T6, six of which have been announced earlier in Mainzer et al and Burgasser et al. We present color-color and color-type diagrams showing the locus of M, L, T, and Y dwarfs in WISE color space. Near-infrared classifications as late as early Y are presented and objects with peculiar spectra are discussed. After deriving an absolute WISE 4.6 um (W2) magnitude vs. spectral type relation, we estimate spectrophotometric distances to our discoveries. We also use available astrometric measurements to provide preliminary trigonometric parallaxes to four our discoveries, which have types of L9 pec (red), T8, T9, and Y0; all of these lie within 10 pc of the Sun. The Y0 dwarf, WISE 1541-2250, is the closest at 2.8 (+1.3,-0.6) pc; if this 2.8 pc value persists after continued monitoring, WISE 1541-2250 will become the seventh closest stellar system to the Sun. Another ten objects, with types between T6 and >Y0, have spectrophotometric distance estimates also placing them within 10 pc. The closest of these, the T6 dwarf WISE 1506+7027, is believed to fall at a distance of roughly 4.9 pc. WISE multi-epoch positions supplemented with positional info primarily from Spitzer/IRAC allow us to calculate proper motions and tangential velocities for roughly one half of the new discoveries. This work represents the first step by WISE to complete a full-sky, volume-limited census of late-T and Y dwarfs. Using early results from this census, we present preliminary, lower limits to the space density of these objects and discuss constraints on both the functional form of the mass function and the low-mass limit of star formation.

astro-ph.SR↗

arXiv2011

FIRE Spectroscopy of Five Late-type T Dwarfs Discovered with the Wide-field Infrared Survey Explorer

We present the discovery of five late-type T dwarfs identified with the Wide-field Infrared Survey Explorer (WISE). Low-resolution near-infrared spectroscopy obtained with the Magellan Folded-port InfraRed Echellette (FIRE) reveal strong water and methane absorption in all five sources, and spectral indices and comparison to spectral templates indicate classifications ranging from T5.5 to T8.5:. The spectrum of the latest-type source, WISE J1812+2721, is an excellent match to that of the T8.5 companion brown dwarf Wolf 940B. WISE-based spectrophotometric distance estimates place these T dwarfs at 12-13 pc from the Sun, assuming they are single. Preliminary fits of the spectral data to the atmosphere models of Saumon & Marley indicate effective temperatures ranging from 600 K to 930 K, both cloudy and cloud-free atmospheres, and a broad range of ages and masses. In particular, two sources show evidence of both low surface gravity and cloudy atmospheres, tentatively supporting a trend noted in other young brown dwarfs and exoplanets. In contrast, the high proper motion T dwarf WISE J2018-7423 exhibits a suppressed K-band peak and blue spectrophotometric J-K colors indicative of an old, massive brown dwarf; however, it lacks the broadened Y-band peak seen in metal-poor counterparts. These results illustrate the broad diversity of low-temperature brown dwarfs that will be uncovered with WISE.

astro-ph.SR↗