Hydrocarbon species, and in particular CH4, play a key role in the
stratosphere--thermosphere boundary of Jupiter, which occurs around the
μ-bar pressure level. Previous analyses of solar occultation, He and
Ly-α airglow, and ISO/SWS measurements of the radiance around 3.3 μm
have inferred significantly different methane concentrations. Here we aim to
accurately model the CH4 radiance at 3.3 μm measured by ISO/SWS by using
a comprehensive non-local thermodynamic equilibrium model and the most recent
collisional rates measured in the laboratory for CH4 to shed new light onto
the methane concentration in the upper atmosphere of Jupiter. These emission
bands have been shown to present a peak contribution precisely at the μ-bar
level, hence directly probing the region of interest. We find that a high
CH4 concentration is necessary to explain the data, in contrast with the
most recent analyses, and that the observations favour the lower limit of the
latest laboratory measurements of the CH4 collisional relaxation rates. Our
results provide precise constraints on the composition and dynamics of the
lower atmosphere of Jupiter.Comment: 15 pages; accepted for publication in A&