The temperature structure of a giant planet was traditionally thought to be an adiabat assuming convective mixing homogenizes entropy. The only in-situ measurement made by the Galileo Probe detected a near-adiabatic temperature structure within one of Jupiter's 5μm hot spots with small but definite local departures from adiabaticity. We analyze Juno's microwave observations near Jupiter's equator (0 ~ 5oN) and find that the equatorial temperature structure is best characterized by a stable super-adiabatic temperature profile rather than an adiabatic one. Water is the only substance with sufficient abundance to alter the atmosphere's mean molecular weight and prevent dynamic instability if a super-adiabatic temperature gradient exists. Thus, from the super-adiabaticity, our results indicate a water concentration (or the oxygen to hydrogen ratio) of about 4.9 times solar with a possible range of 1.5 ~ 8.3 times solar in Jupiter's equatorial region.
@article{arxiv.2403.05363,
title = {Super-adiabatic Temperature Gradient at Jupiter's Equatorial Zone and Implications for the Water Abundance},
author = {Cheng Li and Michael Allison and Sushil Atreya and Shawn Brueshaber and Leigh N. Fletcher and Tristan Guillot and Liming Li and Jonathan Lunine and Yamila Miguel and Glenn Orton and Paul Steffes and J. Hunter Waite and Michael H. Wong and Steven Levin and Scott Bolton},
journal= {arXiv preprint arXiv:2403.05363},
year = {2024}
}