11:45 〜 12:00
[PPS01-10] Constraints on the geology of Ganymede from Juno gravity data
キーワード：Jupiter, Juno, Ganymede, Europa, Io, Gravity
NASA’s Juno extended mission has provided the opportunity for the first close flybys of the Galilean satellites—Ganymede (June 2021), Europa (September 2022), and Io (December 2023, February 2024)—since the Galileo mission at the turn of the millennium. Doppler tracking of the spacecraft during these flybys, in combination with data from Galileo, has enabled the development of improved models for the gravity fields of these worlds. The first updated gravity model was reported by Gomez Casajus et al. (2022), who derived a new gravity model for Ganymede, complete to spherical harmonic degree/order 5 (equivalent to a spatial wavelength of approximately 3,000 km). We can expect that Juno will also provide constraints on the long-wavelength gravity field of Europa and Io (although the quality of the gravity field will vary between the moons).
Long-wavelength gravity can provide key constraints on the interior structure and geologic processes of planetary bodies. In particular, spherical harmonic degree/order-2 gravity is related to both the radial density structure, and how the body deforms in response to rotation and tides. However, every time we investigate planetary gravity fields in more detail, we consistently find that long-wavelength gravity is more complicated. Geologic processes—including impacts, volcanism, volatile loading, tectonics, etc.—all contribute to long-wavelength gravity of planetary bodies.
In this presentation, we will present a preliminary investigation comparing the new, Juno-derived gravity model of Ganymede to expectations for the gravity field arising from geologic features. The spatial pattern of observed gravity anomalies on Ganymede appears reminiscent of the long-wavelength patterns of Ganymede’s light and dark terrains. Dark terrains are heavily cratered (and thus ancient), whereas light terrains are less extensively cratered (and thus younger) and associated with extensive cross-cutting grooves which may arise from tectonic and/or cryovolcanic processes (e.g., Pappalardo et al. 2004, Collins et al. 2014). The magnitude of the observed gravity anomalies (±20 mGal) could imply that the light terrain has a lower elevation and/or lower crustal density than the dark terrains. However, given the limited quality of the available data, and the lack of many key datasets (e.g., global topography), this correlation and interpretation remains speculative. The forthcoming ESA JUICE mission, which will orbit Ganymede, will yield substantial insights.
Finally, we will also present preliminary models for expectations for how geologic features on both Europa and Io may manifest in Juno gravity data.
Long-wavelength gravity can provide key constraints on the interior structure and geologic processes of planetary bodies. In particular, spherical harmonic degree/order-2 gravity is related to both the radial density structure, and how the body deforms in response to rotation and tides. However, every time we investigate planetary gravity fields in more detail, we consistently find that long-wavelength gravity is more complicated. Geologic processes—including impacts, volcanism, volatile loading, tectonics, etc.—all contribute to long-wavelength gravity of planetary bodies.
In this presentation, we will present a preliminary investigation comparing the new, Juno-derived gravity model of Ganymede to expectations for the gravity field arising from geologic features. The spatial pattern of observed gravity anomalies on Ganymede appears reminiscent of the long-wavelength patterns of Ganymede’s light and dark terrains. Dark terrains are heavily cratered (and thus ancient), whereas light terrains are less extensively cratered (and thus younger) and associated with extensive cross-cutting grooves which may arise from tectonic and/or cryovolcanic processes (e.g., Pappalardo et al. 2004, Collins et al. 2014). The magnitude of the observed gravity anomalies (±20 mGal) could imply that the light terrain has a lower elevation and/or lower crustal density than the dark terrains. However, given the limited quality of the available data, and the lack of many key datasets (e.g., global topography), this correlation and interpretation remains speculative. The forthcoming ESA JUICE mission, which will orbit Ganymede, will yield substantial insights.
Finally, we will also present preliminary models for expectations for how geologic features on both Europa and Io may manifest in Juno gravity data.