Meteorites & Asteroids

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

By Keith Cowing
Status Report
October 4, 2023
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Outgassing Composition of the Murchison Meteorite: Implications for Volatile Depletion of Planetesimals and Interior-atmosphere Connections for Terrestrial Exoplanets
Experimentally measured outgassing composition of a 3 mg powdered Murchison sample from 200 °C–1200 ◦ C under a high-vacuum environment (∼10−4 Pa at lower temperatures and ∼10−3 Pa at higher temperatures; lower panel) compared with the outgassing trends of S and Zn under the same vacuum conditions from this study (upper panel). In the lower panel, the outgassing composition is shown as mole fractions of different outgassed species on a log scale as a function of temperature. The outgassing composition of Murchison was determined using a residual gas analyzer mass spectrometer that monitored the abundances (i.e., mole fractions) of the highly volatile outgassing species H2O, H2, CO, CO2, and H2S (see Thompson et al. 2021 for further details). Each species is labeled, and its mass number (in amu) is in parentheses. The dashed curves show equilibrium model-adjusted experimental outgassing compositions, which are the result of taking Thompson et al.’s (2021) experimental elemental outgassing results at intervals of 50 ◦ C and inputting those into the chemical equilibrium model of Figure 5 (see Schaefer & Fegley 2007, 2010 for details on the model) to recompute how the gas composition would speciate under equilibrium conditions. The upper panel shows the S and Zn outgassing trends from this study, expressed as these elements’ intensities, normalized to V and the average of the two unheated Murchison samples, for the residues heated under vacuum. — astro-ph.EP

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.

Maggie A. Thompson, Myriam Telus, Graham Harper Edwards, Laura Schaefer, Jasmeet Dhaliwal, Brian Dreyer, Jonathan J. Fortney, Kyle Kim

Comments: 23 pages, 11 figures, 15 tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2310.02028 [astro-ph.EP] (or arXiv:2310.02028v1 [astro-ph.EP] for this version)
Journal reference: Planet. Sci. J. 4 185 (2023)
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From: Maggie Thompson
[v1] Tue, 3 Oct 2023 13:14:28 UTC (2,088 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻