Planets or asteroids? A geochemical method to constrain the masses of White Dwarf pollutants

• Published in: arXiv.org 2021-11
• Main Authors: Buchan, Andrew M, Bonsor, Amy, Shorttle, Oliver, Wade, Jon, Harrison, John, Noack, Lena, Koester, Detlev
• Format: Article
• Language: English
• Subjects: Abundance; Asteroids; Chromium; Deposition; Differentiation; Dwarf planets; Extrasolar planets; Fragments; Planetary systems; Pollutants; Silicon; Terrestrial planets; White dwarf stars
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2111.08779

Polluted white dwarfs that have accreted planetary material provide a unique opportunity to probe the geology of exoplanetary systems. However, the nature of the bodies which pollute white dwarfs is not well understood: are they small asteroids, minor planets, or even terrestrial planets? We present a novel method to infer pollutant masses from detections of Ni, Cr and Si. During core--mantle differentiation, these elements exhibit variable preference for metal and silicate at different pressures (i.e., object masses), affecting their abundances in the core and mantle. We model core--mantle differentiation self-consistently using data from metal--silicate partitioning experiments. We place statistical constraints on the differentiation pressures, and hence masses, of bodies which pollute white dwarfs by incorporating this calculation into a Bayesian framework. We show that Ni observations are best suited to constraining pressure when pollution is mantle-like, while Cr and Si are better for core-like pollution. We find 3 systems (WD0449-259, WD1350-162 and WD2105-820) whose abundances are best explained by the accretion of fragments of small parent bodies (\(