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Infrared observations by Juno/JIRAM reveal local surface composition on Ganymede

Presentation #504.03 in the session Galilean Satellites: Scratching the Surface (Oral Presentation)

Published onOct 23, 2023
Infrared observations by Juno/JIRAM reveal local surface composition on Ganymede

Since its orbital insertion at Jupiter, the Jovian InfraRed Auroral Mapper (JIRAM) onboard the NASA Juno spacecraft has observed Ganymede over 5500 times, both with its infrared imaging subsystem and with its slit spectrometer sensitive to the 2-5 µm spectral range.

Ganymede, the largest natural satellite of Jupiter and of our Solar System, shows dark geological provinces, indicative of an older age, alternating with brighter and younger terrains. This geological diversity is accompanied by a difference in surface composition. Previous observations obtained by both NASA’s Galileo spacecraft and ground-based telescopes have revealed the presence of both water ice and non-ice material indicative of endogenous compounds, exogenous compounds, or a combination thereof. Juno was designed above all for the study of Jupiter, but in recent years the natural evolution of its orbit has allowed close encounters with some of the Galilean satellites. On June 7, 2021, Juno flew over Ganymede from a minimum altitude of just over 1000 km, obtaining pixel resolution values <1 km. The infrared spectra returned by JIRAM at low northern latitudes and in the sub-Jovian hemisphere made it possible to discriminate the spectral signatures of several chemical compounds including organics, some of which are only observable at a local scale. We discuss these results, and emphasize the correlation with specific geological features, suggesting that the composition observed by JIRAM in the explored region is predominantly endogenous, possibly resulting from underground brine extrusion, and relatively unaffected by substantial exogenous effects.

These results are key in preparation for future measurements to be returned by ESA’s JUICE mission, which aims to achieve global coverage of Ganymede in the 2030s.


JIRAM is funded by the Italian Space Agency (ASI), ASI‐INAF contract n. 2016‐23‐H.0 plus addendum n. 2016-23-H.2-2021. The JIRAM instrument was built by Selex ES, under the leadership of the Italian National Institute for Astrophysics, Institute for Space Astrophysics and Planetology (INAF‐IAPS), Rome, Italy. JIRAM is operated by INAF‐IAPS, Rome, Italy. Support of the Juno Science and Operations Teams is gratefully acknowledged.

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