TY - JOUR
T1 - Experimental Determination of Mantle Solidi and Melt Compositions for Two Likely Rocky Exoplanet Compositions
AU - Brugman, K.
AU - Phillips, M. G.
AU - Till, C. B.
N1 - Funding Information:
Thank you to associate editor Ananya Mallik and to Chris Renggli and two anonymous reviewers whose feedback and insightful questions helped to enrich this manuscript. Thanks to Axel Wittmann, Chelsea Allison, Stephanie Brown, Steve Desch, Sierra Ferguson, Crystylynda Fudge, Chris Haberle, Rick Hervig, Natalie Hinkel, Kayla Iacovino, Aleisha Johnson, Thad Komacek, Heather Meyer, Kurt Roggensack, Everett Shock, Cayman Unterborn, Jax Webb, and the EPIC group at ASU. The results reported herein benefited from collaborations and/or information exchange within NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. The research shown here acknowledges use of the Hypatia Catalog Database, an online compilation of stellar abundance data as described in Hinkel et al. (2014, , 148, 54), which was supported by NExSS and the Vanderbilt Initiative in Data‐Intensive Astrophysics (VIDA). This work was supported by the U.S. National Science Foundation under Graduate Research Fellowship no. 026257‐001 to K.K.B., an ASU Graduate College Completion Fellowship to K.K.B, an ASU College of Liberal Arts and Sciences Undergraduate Summer Research Fellowship to M.G.P., and the ASU‐NExSS grant (NNX15AD53G to Steve Desch). The EPMA facilities at ASU are in part supported by the National Nanotechnology Coordinated Infrastructure grant ECCS‐1542160. AJ
Funding Information:
Thank you to associate editor Ananya Mallik and to Chris Renggli and two anonymous reviewers whose feedback and insightful questions helped to enrich this manuscript. Thanks to Axel Wittmann, Chelsea Allison, Stephanie Brown, Steve Desch, Sierra Ferguson, Crystylynda Fudge, Chris Haberle, Rick Hervig, Natalie Hinkel, Kayla Iacovino, Aleisha Johnson, Thad Komacek, Heather Meyer, Kurt Roggensack, Everett Shock, Cayman Unterborn, Jax Webb, and the EPIC group at ASU. The results reported herein benefited from collaborations and/or information exchange within NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. The research shown here acknowledges use of the Hypatia Catalog Database, an online compilation of stellar abundance data as described in Hinkel et?al. (2014, AJ, 148, 54), which was supported by NExSS and the Vanderbilt Initiative in Data-Intensive Astrophysics (VIDA). This work was supported by the U.S. National Science Foundation under Graduate Research Fellowship no. 026257-001 to K.K.B., an ASU Graduate College Completion Fellowship to K.K.B, an ASU College of Liberal Arts and Sciences Undergraduate Summer Research Fellowship to M.G.P., and the ASU-NExSS grant (NNX15AD53G to Steve Desch). The EPMA facilities at ASU are in part supported by the National Nanotechnology Coordinated Infrastructure grant ECCS-1542160.
Publisher Copyright:
© 2021. American Geophysical Union. All Rights Reserved.
PY - 2021/7
Y1 - 2021/7
N2 - For rocky exoplanets, knowledge of their geologic characteristics such as composition and mineralogy, surface recycling mechanisms, and volcanic behavior are key to determining their suitability to host life. Thus, determining exoplanet habitability requires an understanding of surface chemistry, and understanding the composition of exoplanet surfaces necessitates applying methods from the field of igneous petrology. Piston-cylinder partial melting experiments were conducted on two hypothetical rocky exoplanet bulk silicate compositions. HEX1, a composition with molar Mg/Si = 1.42 (higher than bulk silicate Earth's Mg/Si = 1.23) yields a solidus similar to that of Earth's undepleted mantle. However, HEX2, a composition with molar Ca/Al = 1.07 (higher than Earth Ca/Al = 0.72) has a solidus with a slope of ∼10°C/kbar (vs. ∼15°C/kbar for Earth) and as result, has much lower melting temperatures than Earth. The majority of predicted adiabats point toward the likely formation of a silicate magma ocean for exoplanets with a mantle composition similar to HEX2. For adiabats that do intersect HEX2's solidus, decompression melting initiates at pressures more than 4x greater than in the modern Earth's undepleted mantle. The experimental partial melt compositions for these exoplanet mantle analogs are broadly similar to primitive terrestrial magmas but with higher CaO, and for the HEX2 composition, higher SiO2 for a given degree of melting. This first of its kind exoplanetary experimental data can be used to calibrate future exoplanet petrologic models and predict volatile solubilities, volcanic degassing, and crust compositions for exoplanets with bulk compositions and ƒO2 similar to those explored herein.
AB - For rocky exoplanets, knowledge of their geologic characteristics such as composition and mineralogy, surface recycling mechanisms, and volcanic behavior are key to determining their suitability to host life. Thus, determining exoplanet habitability requires an understanding of surface chemistry, and understanding the composition of exoplanet surfaces necessitates applying methods from the field of igneous petrology. Piston-cylinder partial melting experiments were conducted on two hypothetical rocky exoplanet bulk silicate compositions. HEX1, a composition with molar Mg/Si = 1.42 (higher than bulk silicate Earth's Mg/Si = 1.23) yields a solidus similar to that of Earth's undepleted mantle. However, HEX2, a composition with molar Ca/Al = 1.07 (higher than Earth Ca/Al = 0.72) has a solidus with a slope of ∼10°C/kbar (vs. ∼15°C/kbar for Earth) and as result, has much lower melting temperatures than Earth. The majority of predicted adiabats point toward the likely formation of a silicate magma ocean for exoplanets with a mantle composition similar to HEX2. For adiabats that do intersect HEX2's solidus, decompression melting initiates at pressures more than 4x greater than in the modern Earth's undepleted mantle. The experimental partial melt compositions for these exoplanet mantle analogs are broadly similar to primitive terrestrial magmas but with higher CaO, and for the HEX2 composition, higher SiO2 for a given degree of melting. This first of its kind exoplanetary experimental data can be used to calibrate future exoplanet petrologic models and predict volatile solubilities, volcanic degassing, and crust compositions for exoplanets with bulk compositions and ƒO2 similar to those explored herein.
KW - exoplanet
KW - experimental petrology
KW - melt initiation
KW - melt migration
KW - partial melting
KW - volatile saturation
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U2 - 10.1029/2020JE006731
DO - 10.1029/2020JE006731
M3 - Article
AN - SCOPUS:85111701091
VL - 126
JO - Journal of Geophysical Research: Planets
JF - Journal of Geophysical Research: Planets
SN - 2169-9097
IS - 7
M1 - e2020JE006731
ER -