^1,2K. K. Brugman,^1,3M. G. Phillips,¹C. B. Till
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2020JE006731]
¹School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
²Earth & Planets Laboratory, Carnegie Institution for Science, Washington, D.C. USA
³United States Geological Survey, Moffett Field, CA USA
Published by arrangement with John Wiley & Sons

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 (versus ∼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.

^1,2Amanda A.Tosi,²Maria Elizabeth Zucolotto,³Wania Wolff,¹Julio C.Mendes,⁴Sergio Suárez,^5,6Pablo Daniel Pérez,⁷Diana P.P.Andrade
Planetary and Space Science (in Press) Link to Article [https://doi.org/10.1016/j.pss.2021.105250]
¹LABSONDA/IGEO/UFRJ, Instituto de Geociências, Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 274, Cidade Universitária, 21941-972, Rio de Janeiro, RJ, Brazil
²LABET/MN/UFRJ, Laboratório Extraterrestre, Departamento de Geologia e Paleontologia, Museu Nacional, Universidade Federal do Rio de Janeiro, Quinta da Boa Vista, São Cristóvão, 20940-040 Rio de Janeiro, RJ, Brazil
³Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil
⁴Divisiones Atômicas, Centro Atomico Bariloche (CONICET), Av. Bustillo 10000, San Carlos de Bariloche, Argentina
⁵Departamento de Ciencias Físicas, Universidad de La Frontera (UFRO), Temuco, Chile
⁶Centro de Física e Ingeniería en Medicina (CFIM), Universidad La Frontera (UFRO), Temuco, Chile
⁷Observatório do Valongo, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brazil

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