The Survival of Water within Extrasolar Minor Planets

TL;DR

This paper suggests that extrasolar minor planets can retain water during stellar evolution, and their accretion onto white dwarfs could explain observed hydrogen and oxygen pollution, implying widespread water-rich bodies in the galaxy.

Contribution

It introduces a model for water retention in extrasolar minor planets and proposes observational tests for water-rich bodies via white dwarf pollution analysis.

Findings

Extrasolar minor planets can retain internal water during red giant phases.

Accretion of water-rich bodies onto white dwarfs can explain hydrogen and oxygen pollution.

Potential for widespread liquid water environments in the Milky Way.

Abstract

We compute that extrasolar minor planets can retain much of their internal H_2O during their host star's red giant evolution. The eventual accretion of a water-rich body or bodies onto a helium white dwarf might supply an observable amount of atmospheric hydrogen, as seems likely for GD 362. More generally, if hydrogen pollution in helium white dwarfs typically results from accretion of large parent bodies rather than interstellar gas as previously supposed, then H_2O probably constitutes at least 10% of the aggregate mass of extrasolar minor planets. One observational test of this possibility is to examine the atmospheres of externally-polluted white dwarfs for oxygen in excess of that likely contributed by oxides such as SiO_2. The relatively high oxygen abundance previously reported in GD 378 plausibly but not uniquely can be explained by accretion of an H_2O-rich parent body or bodies. Future ultraviolet observations of white dwarf pollutions can serve to investigate the hypothesis that environments with liquid water that are suitable habitats for extremophiles are widespread in the Milky Way.