Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets

Abstract

Peering inside extrasolar rocky bodies The oxygen fugacity of a rock, f O 2 , is a measure of how oxidizing or reducing its surroundings were when the rock formed. Different minerals form at different f O 2 and have different physical properties, so the internal structure of an exoplanet depends on this value. Doyle et al. exploited the signature left behind when rocky bodies impact a white dwarf—the remnant of a dead star. By examining the rock-forming elements left on the surface of each white dwarf, they determine f O 2 in the impacting body. Six systems all had similar f O 2 to bodies in the Solar System, consistent with the idea that rocky exoplanets often have internal properties similar to those of Earth and Mars. Science , this issue p. 356