Exoplanets, -moons, -comets

From Hubble to HWO: Bridging the Frontier of White Dwarf Exoplanet Science

By Keith Cowing
Status Report
astro-ph.IM
May 28, 2026
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From Hubble to HWO: Bridging the Frontier of White Dwarf Exoplanet Science
The logarithmic number ratios of elemental abundances (ordered in increasing volatility/decreasing condensation temperature) relative to Mg for the planetary material accreting onto four white dwarfs, normalized to solar composition (black dashed line at [X/Mg] = 0) for (a) Earth-like material (M. Jura et al. 2015), (b) icy water-rich material (S. Xu et al. 2017), (c) mantle-rich material (L. K. Rogers et al. 2024a,b), (d) core-rich material (J. T. Williams et al. 2025). The gray region shows the abundance ratios for main sequence FG stars (N. R. Hinkel et al. 2014), and the lines show the abundances of bulk Earth, CI chondrites, Earth’s mantle, and Earth’s core (assuming 90% core and 10% mantle) for comparison (W. F. McDonough 2003; K. Lodders et al. 2009, 2025). With the exception of Ca and Ti, which are only detectable optically, all these diagnostic elements require HST UV spectroscopy for high-precision measurements. — astro-ph.IM

White dwarf stars, the endpoint of stellar evolution for 97% of stars in our Milky Way, offer a unique and powerful window into the bulk elemental composition of rocky exoplanetary bodies.

Up to 50% of single white dwarfs are observed with photospheric metal lines from accreted exoplanetary bodies (called ‘polluted’ white dwarfs), and spectroscopic observations reveal the bulk composition of this material.

High-resolution (R>15,000) UV spectra are essential for detecting many elements present in the material, such as the volatile elements imperative for habitability studies (C, N, O, P, S) and key rock-forming elements required to constrain interior structure (e.g. Fe, Si, Mg, Al, Ni). HST, through its COS and STIS spectrographs, remains the only facility capable of performing this science in the near future.

Looking to the next decade, the scientific case for continued HST UV observations of polluted white dwarfs is compelling on three fronts (i) as a standalone to enable the bulk composition of exoplanetary material to be measured in a statistically significant sample, (ii) as essential groundwork for the Habitable Worlds Observatory (HWO), and (iii) in a powerful synergy with JWST, to enable characterization of the bulk mineralogy and bulk elemental composition of exoplanetary material.

This white paper argues that continued UV spectroscopic capabilities with HST is a high-return investment for white dwarf and exoplanet science, and preserving and prioritizing HST’s UV capabilities through at least 2035 is crucial to maximize the scientific return from HST, JWST, and HWO.

Laura K. Rogers, Siyi Xu, Martin Barstow, Simon Blouin, Amy Bonsor, Andrew M. Buchan, Sarah L. Casewell, Tim Cunningham, John Debes, Patrick Dufour, Boris Gansicke, Joseph Guidry, Ted von Hippel, Mukremin Kilic, Erika Le Bourdais, Carl Melis, Lou Baya Ould Rouis, Judith Provencal, Melinda Soares-Furtado, Andrew Swan, Isabella Trierweiler, Zachary Vanderbosch, Jamie Williams

Comments: White paper submitted to STScI call: Building a Roadmap for Hubble science into the 2030s
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2605.26142 [astro-ph.IM](or arXiv:2605.26142v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2605.26142
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Submission history
From: Laura Rogers
[v1] Fri, 22 May 2026 19:49:03 UTC (1,548 KB)
https://arxiv.org/abs/2605.26142

Astrobiology, exoplanet,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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