An optical transmission spectrum for the ultra-hot Jupiter WASP-121b measured with the Hubble Space Telescope

An optical transmission spectrum for the ultra-hot Jupiter WASP-121b measured with the Hubble Space Telescope by T.M. Evans, CSI member Nikole Lewis, and colleagues; email: nikole.lewis@cornell.edu

We present an atmospheric transmission spectrum for the ultra-hot Jupiter WASP-121b, measured using the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope (HST). Across the 0.47-1 micron wavelength range, the data imply an atmospheric opacity comparable to - and in some spectroscopic channels exceeding - that previously measured at near-infrared wavelengths (1.15-1.65 micron). Wavelength-dependent variations in the opacity rule out a gray cloud deck at a confidence level of 3.8-sigma and may instead be explained by VO spectral bands. We find a cloud-free model assuming chemical equilibrium for a temperature of 1500K and metal enrichment of 10-30x solar matches these data well. Using a free-chemistry retrieval analysis, we estimate a VO abundance of -6.6(-0.3,+0.2) dex. We find no evidence for TiO and place a 3-sigma upper limit of -7.9 dex on its abundance, suggesting TiO may have condensed from the gas phase at the day-night limb. The opacity rises steeply at the shortest wavelengths, increasing by approximately five pressure scale heights from 0.47 to 0.3 micron in wavelength. If this feature is caused by Rayleigh scattering due to uniformly-distributed aerosols, it would imply an unphysically high temperature of 6810+/-1530K. One alternative explanation for the short-wavelength rise is absorption due to SH (mercapto radical), which has been predicted as an important product of non-equilibrium chemistry in hot Jupiter atmospheres. Irrespective of the identity of the NUV absorber, it likely captures a significant amount of incident stellar radiation at low pressures, thus playing a significant role in the overall energy budget, thermal structure, and circulation of the atmosphere.

Nikole Lewis, Astronomy & Planetary Science

Klarman Hall at sunset

Tweets from CSInst

"On the Correlation between Hot Jupiters and Stellar Clustering: High-Eccentricity Migration Induced by Stellar Fly… https://t.co/KBs39nU8NS
4 days 1 hour ago
“There are a bunch of elements of Mars Sample Return that are demonstrating key technologies required to safely sen… https://t.co/TR7dH0n2zr
4 days 1 hour ago
"This is really the start of a much larger endeavor. It’s more than just a single mission, it’s the start of a camp… https://t.co/KDReeaigbM
4 days 1 hour ago
'Seven Hundred Leagues Beneath Titan’s Methane Seas' “The depth and composition of each of Titan's seas had alrea… https://t.co/UOApnHmixx
4 days 1 hour ago
“This is really the first opportunity to look for life.” Jonathan Lunine, chair of the Department of Astronomy at C… https://t.co/MCXLHtW9ye
4 days 1 hour ago
"The Perseverance rover is just step 1 of 3 in the concept of Mars sample return. Our job is to land at Jezero, ide… https://t.co/UZpLDfS6bb
4 days 1 hour ago