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arXiv · 2507.16777

Silicate mineralogy and bulk composition of exoplanetary material in polluted white dwarfs

Laura K. Rogers·Amy Bonsor·Érika Le Bourdais·Siyi Xu·Kate Y. L. Su·Benjamin Richards·Andrew Buchan·Nicholas P. Ballering·Marc Brouwers·Patrick Dufour·Markus Kissler-Patig·Carl Melis·Ben Zuckerman
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Abstract

White dwarf planetary systems uniquely link the bulk elemental composition of exoplanetary material to the mineralogy as photospheric abundances can be compared to circumstellar dust mineralogy. This study re-examines Spitzer/IRS spectra of eight white dwarfs with both circumstellar dust and photospheric metals. All systems show 10$μ$m silicate emission features consistent with a mixture of olivine and pyroxene silicates, with varying dominance. New Hubble Space Telescope ultraviolet spectroscopic observations of two of these systems, GD56 and WD1150-153, reveal that both are accreting dry, rocky material. WD1150-153 is accreting material consistent with Bulk Earth, while GD56 is accreting core-rich material with an inferred core mass fraction of 0.59$^{+0.08}_{-0.09}$ (0.37$^{+0.08}_{-0.08}$ by mole). A comparison between the bulk elemental composition of the accreted planetary material and the dust mineralogy of the eight systems reveals a tentative correlation between the dominant silicate mineralogy and the Mg/Si ratio, indicating that the circumstellar and photospheric material are compositionally similar. This suggests that rapid and well-mixed accretion is occurring with minimal compositional alteration. Furthermore, new GGCHEM equilibrium chemistry models confirm that Mg-rich planetary material preferentially forms olivine-rich dust, highlighting the importance of equilibrium in planetary chemistry and that a host star or rock's Mg/Si can be used to predict whether its silicate mineralogy is olivine- or pyroxene-dominated, influencing its capacity to structurally store water, recycle key nutrients, and possibly habitability.

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Laura K. Rogers, Amy Bonsor, Érika Le Bourdais, Siyi Xu, Kate Y. L. Su, Benjamin Richards, Andrew Buchan, Nicholas P. Ballering, Marc Brouwers, Patrick Dufour, Markus Kissler-Patig, Carl Melis, Ben Zuckerman. 2025-07-22. Silicate mineralogy and bulk composition of exoplanetary material in polluted white dwarfs. https://arxiv.org/abs/2507.16777

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