Evidence for post-nebula volatilisation in an exo-planetary body

TL;DR

This study provides evidence that exo-planetary bodies can lose volatile elements after nebula dissipation, likely due to impacts or radioactive heating, affecting their composition and potential habitability.

Contribution

It introduces observational evidence for post-nebula volatile loss in exo-planetary bodies through white dwarf pollution analysis, highlighting a magma ocean stage.

Findings

High Mn/Na ratio in GD362 suggests volatile loss after nebula dissipation.

Heating during star's giant branch phase is insufficient to explain observed composition.

Potential evidence for a magma ocean stage on the exo-planetary body.

Abstract

The loss and gain of volatile elements during planet formation is key for setting their subsequent climate, geodynamics, and habitability. Two broad regimes of volatile element transport in and out of planetary building blocks have been identified: that occurring when the nebula is still present, and that occurring after it has dissipated. Evidence for volatile element loss in planetary bodies after the dissipation of the solar nebula is found in the high Mn to Na abundance ratio of Mars, the Moon, and many of the solar system's minor bodies. This volatile loss is expected to occur when the bodies are heated by planetary collisions and short-lived radionuclides, and enter a global magma ocean stage early in their history. The bulk composition of exo-planetary bodies can be determined by observing white dwarfs which have accreted planetary material. The abundances of Na, Mn, and Mg have been measured for the accreting material in four polluted white dwarf systems. Whilst the Mn/Na abundances of three white dwarf systems are consistent with the fractionations expected during nebula condensation, the high Mn/Na abundance ratio of GD362 means that it is not (>3 sigma). We find that heating of the planetary system orbiting GD362 during the star's giant branch evolution is insufficient to produce such a high Mn/Na. We, therefore, propose that volatile loss occurred in a manner analogous to that of the solar system bodies, either due to impacts shortly after their formation or from heating by short-lived radionuclides. We present potential evidence for a magma ocean stage on the exo-planetary body which currently pollutes the atmosphere of GD362.