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Probing the Atmospheres of Jupiter’s Icy Satellites in the Ultraviolet with Occultations

Presentation #311.06 in the session Future Missions and Instrumentations - Icy Bodies, Exoplanets, Stars (Poster)

Published onOct 23, 2023
Probing the Atmospheres of Jupiter’s Icy Satellites in the Ultraviolet with Occultations

The surfaces of Jupiter’s icy moons are the primary interface between their interiors and the intense Jovian magnetosphere. Surface materials are sublimated and sputtered, generating tenuous atmospheres. Determining the composition of these atmospheres is, therefore, a means of understanding material transport between the subsurface and atmosphere. Additionally, if these satellites are indeed habitable, their surfaces likely represent crucial boundaries across which essential materials are exchanged between the magnetosphere and the extraterrestrial ecosystems below the ice.

Water vapor and its dissociation products present diagnostic features in the extreme ultraviolet, as do other atoms and light molecules in the Jovian environment. Thus, the ultraviolet spectrographs on ESA’s JUICE and NASA’s Europa Clipper missions are particularly well-suited to the study of Jupiter’s icy satellites. The fifth and sixth instruments in a line of UV spectrographs built at the Southwest Research Institute, Europa-UVS and JUICE-UVS will enable detailed compositional measurements of the atmospheres of Jupiter’s moons. One particularly powerful technique for doing so is observing occultations of bright stars, including the Sun, as Jupiter’s icy satellites pass between them and their spacecraft. Both instruments feature a solar port that is canted away from the nominal optical path and contains baffles and coated mirrors that stop the solar signal down to safe operational levels.

Occultation experiments will play a key role in determining the atmospheric compositions of the icy satellites, with hundreds of such observations planned across both missions. Solar occultations will allow for the detection of trace species in the far UV. In addition to determining atmospheric composition, both instruments can contribute to the determination of the long-wavelength shapes of Jupiter’s moons, with implications for their internal dynamics and evolution. For the prediction of occultations, a catalog of UV-bright sources named CUBS has been built. CUBS contains information on nearly 90,000 stars. We will discuss the science enabled by occultation experiments, as well as how such occultations will be predicted, planned and implemented.

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