Polluted White Dwarfs: Insights regarding the chemistry of terrestrial extrasolar planets

Lead Research Organisation: University of Cambridge
Department Name: Institute of Astronomy

Abstract

Current knowledge on the interiors and the geology of terrestrial exoplanets is
limited. Our best estimates for the interior composition come from observations of the planet's mass and radius, but can lead to degenerate solutions. The frequency of solar system like chemistry and geology in the galaxy is poorly understood. The pollution of
white dwarfs by rocky exo-planetary material provides a unique opportunity to study the chemistry and geology of exo-planetary systems. Planetary bodies are scattered inwards from a planetary system that has survived the host star's evolution to the white dwarf phase and accreted by the white dwarfs. Spectra of these polluted white dwarfs yield ratios of key rock forming species, such as Mg/Si, Fe/Si and Ca/Si, as well as ratios of key volatile
species, such as C/O. In this work we propose to use data from various heavily polluted white dwarfs to estimate the chemical composition of extrasolar planetesimals, with an aim to constraining the interior compositions of terrestrial planets. We will present a model that constrains where in a proto-planetary disc the observed pollutants could have formed. This model will take into account potential variations in the host star chemistry. We will use an equilibrium chemistry model, alongside a viscous model for the evolution of a proto-planetary disc, to determine where in the disc the observed compositions could have condensed out of the nebula gas. These results should further our understanding of not only the bulk chemistry of terrestrial planets and the rarity of the solar system's chemistry, but the role host stars play in dictating the chemistry of a terrestrial planet and the role of dynamics in post main sequence systems.

Publications

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J H D Harrison (2018) Polluted White Dwarfs: Insights regarding the origin and geology of Exoplanetary material in Monthly notices of the royal astronomical society

Studentship Projects

Project Reference Relationship Related To Start End Student Name
ST/N503988/1 01/10/2015 30/09/2020
1788855 Studentship ST/N503988/1 01/10/2016 31/03/2020 John Harrison