09:00 〜 09:15
[PPS01-01] Juno/JIRAM Observations of the Galilean Moons
★Invited Papers
The Jupiter InfraRed Auroral Mapper (JIRAM), aboard NASA’s Juno mission, is a spectro-imager primarily designed to investigate atmospheric and auroral phenomena on Jupiter. However, the natural evolution of Juno’s orbit has allowed JIRAM to closely observe some of the Galilean moons in recent years. These observations usually take place when these moons randomly enter JIRAM’s field of view.
The surface of Ganymede, the largest moon of Jupiter and the Solar System, is characterized by dark geological regions, which suggest an older age, alternating with lighter, younger areas. This geological diversity is matched by a varying surface composition. Previous observations, made by both NASA’s Galileo spacecraft and ground-based telescopes, have detected both water ice and non-ice materials, pointing to the presence of endogenous compounds, exogenous compounds, or a mixture of both. On June 7, 2021, the Jovian InfraRed Auroral Mapper (JIRAM) spectro-imager onboard Juno performed a flyby of Ganymede, passing at an altitude of just over 1000 km. The infrared spectra collected by JIRAM between 2 and 5 µm, with a ground resolution of less than 1 km, were obtained at low northern latitudes and in the sub-Jovian hemisphere, enabling the identification of spectral signatures from several chemical compounds, including organics, some of which are only observable at local scales. We discuss these findings and highlight their correlation with specific geological features, suggesting that the composition observed by JIRAM in the explored region is predominantly endogenous, likely due to the extrusion of subsurface brines, and remains relatively unchanged thanks to the protective effect of Ganymede’s intrinsic magnetic field.
In addition to Ganymede, JIRAM has focused primarily on observations of Io. Monitoring Io’s hotspots over the early years of the mission, with medium-to-low spatial resolution, initially allowed the identification of hundreds of constantly active hotspots. However, in recent years, JIRAM data led to important findings on Io's volcanic activity. The analysis revealed significant variability in the spectral radiance of Io's hotspots, especially at lower latitudes, where they exhibited higher temperatures and more intense temporal changes. Observations of at least ten paterae, such as Loki and Surt, showed common thermal features like "thermal rings" around their edges, indicating active lava lakes undergoing a vertical, "piston-like" motion. These paterae were not currently experiencing lava overflow, suggesting stable lake levels at the time.
Further analysis identified over 40 paterae, most showing clear thermal signatures, which implies lava lakes are widespread on Io. Crusts in some lakes were found to be just a few years old, and the thermal emissions mainly came from the thicker crust rather than liquid lava edges. Additionally, observations of Loki Patera showed unique thermal patterns, with a significant volume of magma beneath the crust. A thermal wave, likely from resurfacing, was observed moving across the lake at 2-3 km/day, and stable islands in Loki were found to have remained unchanged for over 45 years, challenging current resurfacing models.
These findings offer valuable insights into the dynamic volcanic processes on Io, suggesting active lava lakes, resurfacing, and tidal forces as key factors in its ongoing geological activity.
Acknowledgments:
We thank Agenzia Spaziale Italiana (ASI) for the support of the JIRAM contribution to the Juno mission. This work is funded by the ASI–INAF Addendum no. 2016-23-H.3-2023 to grant 2016-23-H.0.
The surface of Ganymede, the largest moon of Jupiter and the Solar System, is characterized by dark geological regions, which suggest an older age, alternating with lighter, younger areas. This geological diversity is matched by a varying surface composition. Previous observations, made by both NASA’s Galileo spacecraft and ground-based telescopes, have detected both water ice and non-ice materials, pointing to the presence of endogenous compounds, exogenous compounds, or a mixture of both. On June 7, 2021, the Jovian InfraRed Auroral Mapper (JIRAM) spectro-imager onboard Juno performed a flyby of Ganymede, passing at an altitude of just over 1000 km. The infrared spectra collected by JIRAM between 2 and 5 µm, with a ground resolution of less than 1 km, were obtained at low northern latitudes and in the sub-Jovian hemisphere, enabling the identification of spectral signatures from several chemical compounds, including organics, some of which are only observable at local scales. We discuss these findings and highlight their correlation with specific geological features, suggesting that the composition observed by JIRAM in the explored region is predominantly endogenous, likely due to the extrusion of subsurface brines, and remains relatively unchanged thanks to the protective effect of Ganymede’s intrinsic magnetic field.
In addition to Ganymede, JIRAM has focused primarily on observations of Io. Monitoring Io’s hotspots over the early years of the mission, with medium-to-low spatial resolution, initially allowed the identification of hundreds of constantly active hotspots. However, in recent years, JIRAM data led to important findings on Io's volcanic activity. The analysis revealed significant variability in the spectral radiance of Io's hotspots, especially at lower latitudes, where they exhibited higher temperatures and more intense temporal changes. Observations of at least ten paterae, such as Loki and Surt, showed common thermal features like "thermal rings" around their edges, indicating active lava lakes undergoing a vertical, "piston-like" motion. These paterae were not currently experiencing lava overflow, suggesting stable lake levels at the time.
Further analysis identified over 40 paterae, most showing clear thermal signatures, which implies lava lakes are widespread on Io. Crusts in some lakes were found to be just a few years old, and the thermal emissions mainly came from the thicker crust rather than liquid lava edges. Additionally, observations of Loki Patera showed unique thermal patterns, with a significant volume of magma beneath the crust. A thermal wave, likely from resurfacing, was observed moving across the lake at 2-3 km/day, and stable islands in Loki were found to have remained unchanged for over 45 years, challenging current resurfacing models.
These findings offer valuable insights into the dynamic volcanic processes on Io, suggesting active lava lakes, resurfacing, and tidal forces as key factors in its ongoing geological activity.
Acknowledgments:
We thank Agenzia Spaziale Italiana (ASI) for the support of the JIRAM contribution to the Juno mission. This work is funded by the ASI–INAF Addendum no. 2016-23-H.3-2023 to grant 2016-23-H.0.