Oxygen Fugacities Of Extrasolar Rocks: Evidence for an Earth-like Geochemistry of Exoplanets

Bulk compositions by mass for six white dwarfs compared to Solar System bodies. Bulk compositions of the six rock-forming elements Al, Ca, Si, Mg, Fe and O are indicated by the colored bars. The six white dwarfs are shown in the right-most columns. Shown for comparison are Solar System objects: the Sun, Comet Halley (1P/Halley), Earth, the Moon, Vesta, Mars, Mercury, three types of meteorites (enstatite chondrite, ordinary L chondrite, and carbonaceous CI chondrite), and three terrestrial igneous rock types: mid ocean ridge basalt (MORB), lherzolite (representing Earth’s mantle) and bulk silicate Earth (BSE) (16). The relatively high abundances of Fe in bulk Mercury and bulk Earth are due to their metal cores. The compositions of the white dwarfs are similar to the Solar System rocks. The large amount of O in WD 1145+017 is highly uncertain. Values are listed in Data S1.

Oxygen fugacity is a measure of rock oxidation that influences planetary structure and evolution. Most rocky bodies in the Solar System formed at oxygen fugacities approximately five orders of magnitude higher than a hydrogen-rich gas of solar composition.

It is unclear whether this oxidation of rocks in the Solar System is typical among other planetary systems. We exploit the elemental abundances observed in six white dwarfs polluted by the accretion of rocky bodies to determine the fraction of oxidized iron in those extrasolar rocky bodies and therefore their oxygen fugacities.

The results are consistent with the oxygen fugacities of Earth, Mars, and typical asteroids in the Solar System, suggesting that at least some rocky exoplanets are geophysically and geochemically similar to Earth.

Alexandra E. Doyle, Edward D. Young, Beth Klein, Ben Zuckerman, Hilke Schlichting
(Submitted on 28 Oct 2019)
Comments: 12 pages of main text, 3 figures in the main text
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Journal reference: Doyle et al. (2019) Science 366 (6463), 356-359
DOI: 10.1126/science.aax3901
Cite as: arXiv:1910.12989 [astro-ph.EP] (or arXiv:1910.12989v1 [astro-ph.EP] for this version)
Submission history
From: Edward Young
[v1] Mon, 28 Oct 2019 22:13:41 UTC (7,254 KB)
Astrobiology, Astrochemistry

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