Exoplanetology: Exoplanets & Exomoons

Searching for Neutral Hydrogen Escape from the 120 Myr Old Sub-Neptune HIP94235b using HST

By Keith Cowing
Status Report
astro-ph.EP
August 12, 2024
Filed under , , , , , ,
Searching for Neutral Hydrogen Escape from the 120 Myr Old Sub-Neptune HIP94235b using HST
HIP94235 b’s full FUV-MAMA spectrum is depicted in the above figure. The out-of-transit spectrum, derived from orbits 1, 3, 4, and 5 from both visits, is shown in black, while the in-transit spectrum from orbit 2 is plotted in pink, using data from both Visit 1 and Visit 2. The Ly-α model and intrinsic Ly-α profile, generated using the lyapy package (Youngblood et al. 2016), are plotted in blue and navy (dashed), respectively. The shaded regions represent the blue and red wings, with corresponding velocity regions. — astro-ph.EP

HIP94235 b, a 120 Myr old sub-Neptune, provides us the unique opportunity to study mass loss at a pivotal stage of the system’s evolution: the end of a 100 million year (Myr) old phase of intense XUV irradiation.

We present two observations of HIP94235 b using the Hubble Space Telescope’s Space Telescope Imaging Spectrograph (HST/STIS) in the Ly-alpha wavelength region. We do not observe discernible differences across either the blue and red wings of the Ly-alpha line profile in and out of transit, and report no significant detection of outflowing neutral hydrogen around the planet.

We constrain the rate of neutral hydrogen escaping HIP94235 b to an upper limit of 10^13 g/s, which remains consistent with energy-limited model predictions of 10^11 g/s. The Ly-alpha non-detection is likely due to the extremely short photoionization timescale of the neutral hydrogen escaping the planet’s atmosphere.

This timescale, approximately 15 minutes, is significantly shorter than that of any other planets with STIS observations. Through energy-limited mass loss models, we anticipate that HIP94235 b will transition into a super-Earth within a timescale of 1 Gyr.

Ava Morrissey, George Zhou, Chelsea X. Huang, Duncan Wright, Caitlin Auger, Keighley E. Rockcliffe, Elisabeth R. Newton, James G. Rogers, Neale Gibson, Nataliea Lowson, Laura C. Mayorga, Robert A. Wittenmyer

Comments: Accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2408.02170 [astro-ph.EP] (or arXiv:2408.02170v1 [astro-ph.EP] for this version)
Submission history
From: Ava Morrissey
[v1] Mon, 5 Aug 2024 00:19:55 UTC (6,677 KB)
https://arxiv.org/abs/2408.02170

Astrobiology,

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) 🖖🏻

Follow on Twitter
MORE FROM Exoplanetology: Exoplanets & Exomoons