The Gas Composition and Deep Cloud Structure of Jupiter's Great Red Spot

Abstract

We have obtained high-resolution spectra of Jupiter’s Great Red Spot (GRS) between 4.6–5.4 μ m using telescopes on Mauna Kea to derive gas abundances and to constrain its cloud structure between 0.5–5 bars. We used line profiles of deuterated methane (CH 3 D) at 4.66 μ m to infer the presence of an opaque cloud at 5 ± 1 bars. From thermochemical models, this is almost certainly a water cloud. We also used the strength of Fraunhofer lines in the GRS to obtain the ratio of reflected sunlight to thermal emission. The level of the reflecting layer was constrained to be at 570 ± 30 mbar based on fitting strong NH 3  lines at 5.32 μ m. We identify this layer as an ammonia cloud based on the temperature where gaseous NH 3  condenses. We found evidence for a strongly absorbing but not totally opaque cloud layer at pressures deeper than 1.3 bars by combining Cassini/CIRS spectra of the GRS at 7.18 μ m with ground-based spectra at 5 μ m. This is consistent with the predicted level of an NH 4 SH cloud. We also constrained the vertical profile of H 2 O and NH 3 . The GRS spectrum is matched by a saturated H 2 O profile above an opaque water cloud at 5 bars. The pressure of the water cloud constrains Jupiter’s O/H ratio to be at least 1.1 times solar. The NH 3  mole fraction is 200 ± 50 ppm for pressures between 0.7–5 bars. Its abundance is 40 ppm at the estimated pressure of the reflecting layer. We obtained 0.8 ± 0.2 ppm for PH 3 , which is a factor of 2 higher than in the warm collar surrounding the GRS. We detected all five naturally occurring isotopes of germanium in GeH 4  in the GRS. We obtained an average value of 0.35 ± 0.05 ppb for GeH 4 . Finally, we measured 0.8 ± 0.2 ppb for CO in the deep atmosphere.