Presentation #625.02 in the session Planetary Atmospheres - Terrestrial Planets and Mini-Neptunes.
We present direct detections of ongoing atmospheric escape from the 120Myr old sub-Neptune HIP94235b. Understanding exoplanet atmospheres is vital for comprehending the diversity of observed planetary systems. This study will provide key insights into the formation of the radius gap in the small exoplanet population. By directly observing mass loss as it is happening for these planets, we can help constrain the mechanisms that cause atmospheric evaporation and the timescales that they occur over. The focus of our study is HIP94235b, a 120Myr old, 3.2 Earth radius planet on a close-in orbit around a Sun-like star. We make use of multiple visits from HST’s STIS and VLT’s CRIRES+ to probe the hydrogen and helium lines of this transiting planet in search of signals of an evaporating atmosphere. Our findings show that HIP94235b is undergoing rapid evaporation displaying a substantial exosphere exceeding 20 times the planetary size. This is the first time a young planet at this critical age has been observed to undergo escape via a multi-tracer approach.