Astronomy & Telescopes

Building a Roadmap for Hubble Science into the 2030s: Revealing Atmospheric Structure and Evolution in Substellar Worlds Using HST

By Keith Cowing

Status Report

astro-ph.IM

June 22, 2026

Filed under astro-ph.IM, astronomy, atmosphere, exoplanet, Hubble, imaging, Spectroscopy

Building a Roadmap for Hubble Science into the 2030s: Revealing Atmospheric Structure and Evolution in Substellar Worlds Using HST — Left: Schematic illustration of the primary physical drivers of variability in substellar atmospheres (from left to right: aurora, iron clouds obscured by patchy silicate clouds, thermal inversion, and silicate clouds), their relative atmospheric depths and the wavelengths at which their signatures are most clearly observed. The instruments capable of probing these wavelengths and their drivers are shown at the top of the illustration. Right: Rotational light curves from the young, bright T2.5 brown dwarf SIMP J013656.5+093347 from GO 3548 (PI: Vos). Near-infrared variability traces deep cloud layers and higher-atmosphere temperature inversions (green and orange respectively, JWST NIRSpec PRISM), while the mid-infrared feature probes intermediate atmospheric cloud layers (pink, JWST MIRI LRS). JWST requires sequential observations with different instruments and observing modes, the NIR and MIR observations sample different rotations. Ultraviolet auroral emission is expected to originate at the highest atmospheric altitudes but has not yet been detected outside our Solar System. — astro-ph.IM

Substellar objects occupy a unique place in our universe, bridging the gap between the smallest stars and the largest planets, and serving as powerful laboratories for understanding extrasolar atmospheric physics without the contaminating glare of a host star.

Previous studies into the atmospheric structure of these objects have revealed clouds, disequilibrium chemistry, thermal inversions, and auroral processes which each contribute to wavelength-dependent brightness variations.

HST remains uniquely positioned to address key open questions in the field, such as resolving the vertical atmospheric structure, long term evolution of the atmosphere, and detection of UV aurora in the upper atmosphere, primarily in conjunction with other facilities that probe wavelength regimes that cannot be reached with instruments on HST.

We advocate for three large scale initiatives and argue that the study of the atmospheres of substellar worlds directly prepares the community for atmospheric characterization with the Habitable Worlds Observatory.

Allison M. McCarthy, Merle A. Schrader, Johanna M. Vos, Sven Kiefer, Cian O’Toole, Michael K. Plummer, Michael Poon, Daniella Bardalez Gagliuffi, Samuel Beiler, John E. Gizis, Melodie M. Kao, Gabriel-Dominique Marleau, Elisabeth C. Matthews, Philip S. Muirhead, Evert Nasedkin, Natalia Oliveros-Gomez, J. Sebastian Pineda, Kimberly Ward-Duong

Comments: 8 pages, 1 figure
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:2606.18299 [astro-ph.IM] (or arXiv:2606.18299v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2606.18299
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Submission history
From: Allison McCarthy
[v1] Tue, 16 Jun 2026 00:57:41 UTC (235 KB)
https://arxiv.org/abs/2606.18299

Astrobiology, Astrochemistry,

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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