Astrochemistry

Refractory Phosphorus In The HD 100546 Protoplanetary Disk

By Keith Cowing

Status Report

astro-ph.EP

April 22, 2025

Filed under Apatite, Ariel mission, astro-ph.EP, astrochemistry, exoplanet, habitability, HD 100546, Hubble Space Telescope, JWST, Phosphorus, Protoplanet, Protoplanetary Disk, schreibersite, Spectroscopy

Refractory Phosphorus In The HD 100546 Protoplanetary Disk — The dominant phosphorous reservoirs throughout the HD 100546 disk. Left-hand panel: a map of the calculated disk temperature structure, which dictates phosphorous mineral stability. Normalised height above midplane is given by z/r, with height above midplane, z (au), divided by the radial distance, r (au). Hatched regions indicate the two dust rings identified in this system and the dotted black line marks the water iceline (parameterised simply as the 121 K isotherm after Lodders 2003). Right-hand panel: a map of the dominant phosphorous reservoirs in the disk assuming equilibrium at the dust temperature. The minerals apatite, merrillite, and schreibersite progressively replace each other as the main phoshporous reservoir as temperature is increased, up to the point where temperatures are high enough that all major phosphorous-bearing mineral phases have sublimated and most phosphorous is in the gas phase. Phosphorous dissolved in Fe metal is never a dominant reservoir, but its presence is mapped by the dashed contour. Mineral stabilties were taken from Pasek (2019). — astro-ph.EP

The phosphorus budget of planets is intertwined with their formation history and is thought to influence their habitability.

The chemical reservoirs and volatile vs refractory budget of phosphorus in planet-forming environments have so far eluded empirical characterisation. We employ high-resolution spectra from HST/STIS in the ultraviolet and APEX in the sub-mm to constrain the phosphorus budget in the well-characterized HD 100546 star and protoplanetary disk system. We measure log(P/H)_⋆=−7.50+0.23−0.28 on the stellar surface, which traces the total inventory of P in accreting gas and dust from the inner disk.

The inner disk gas, inside of the main dust trap, has log(P/H)_in≲−8.70, and the outer disk gas log(P/H)_out≲−9.30. Phosphorus in the disk is carried by a relatively refractory reservoir, consistent with minerals such as apatite or schreibersite, or with ammonium phosphate salts, in terms of sublimation temperature. We discuss the impact this might have on the two protoplanets around HD 100546.

Our results contribute to our understanding of the chemical habitability of planetary systems and lay a foundation for future explorations, especially in the context of JWST and Ariel which can study phosphorus in exoplanet atmospheres.

Sketch of the HD 100546 system with the star, protoplanetary disk, and two claimed protoplanets. — astro-ph.EP

Mihkel Kama, Oliver Shorttle, Sandipan P. D. Borthakur, Luke Keyte, Jennifer B. Bergner, Luca Fossati, Colin P. Folsom, Heleri Ramler

Comments: 11 pages, 7 figures, accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2504.14228 [astro-ph.EP] (or arXiv:2504.14228v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2504.14228
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Submission history
From: Mihkel Kama
[v1] Sat, 19 Apr 2025 08:35:00 UTC (3,111 KB)
https://arxiv.org/abs/2504.14228
Astrobiology, Astrochemistry,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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