SOFIA Observations of Variability in Jupiter's Para-H2 Distribution and Subsurface Emission Characteristics of the Galilean Satellites

 We observed Jupiter's thermal emission with SOFIA/FORCAST in 2018 August and 2019 July. Both broad-band images (8–37 μm) and spectra (17–37 μm) were obtained. We used the shape of the Jovian spectra to determine the latitudinal distribution of temperatures and para-H2 in the upper troposphere, and compared this to similar data obtained in Fletcher et al. (2017). The two data sets were taken approximately half a Jovian year apart, the first (2014) during northern summer (Ls = 158°) and the second (2019) during southern summer (Ls = 304°). During both epochs the high northern latitudes are cooler than the south. Para-H2 is observed in sub-equilibrium at the equator and in super-equilibrium near the poles during all epochs. The largest difference between the two epochs is the detection of high-para-H2 content at high southern latitudes in 2019, in contrast to the earlier (2014) observations. This implies that the high-latitude para-H2 appears to vary over multi-year timescales. In addition to aiding in the calibration of and providing context to the Jovian spectra, the images were used to determine spectra of the four Galilean satellites. Over the 8–35 μm wavelength range the brightness temperatures of all four satellites drop with increasing wavelength. Although this is expected as longer wavelengths probe the satellites' deeper, cooler layers, our data quantify the brightness temperature gradient with wavelength.