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Jupiter's icy moon Europa is currently seen as the most habitable world closest to Earth. Data from the space mission Galileo supported the presence of a global subsurface water ocean in direct contact with a rocky mantle, implying possible rock-water processes similar to those occurring on Earth's ocean floor, which is teeming with life. Although Juno can provide occasional glimpses of the Galilean satellites, close-up observations are not expected until the arrival of Europa Clipper and JUICE in the Jovian system. In the meantime, radar astronomy can help expand our understanding of this intriguing ocean world.There are ongoing efforts to determine Europa's obliquity from radar echoes observed with the Goldstone Solar System Radar and the Green Bank Telescope [1]. In this contribution, we will present our latest models for icy moon obliquity and nutations, and demonstrate the need for precise modelling of elastic deformation in the ice shell. We will also investigate possible resonant amplification of the obliquity due to ocean dynamics.This work is financially supported by the Belgian Science Policy Office (BELSPO) through the BRAIN.be-2.0 programme.[1] Margot J.-L., Spin states of Europa and Ganymede, European Geosciences Union General Assembly 2025
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This content will become publicly available on March 18, 2026
Spin states of Europa and Ganymede
Radar speckle tracking observations of Europa and Ganymede with the Goldstone Solar System Radar and the Green Bank Telescope in 2011-2023 yield estimates of their spin axis orientations to ~0.01 degrees. These measurements conform to the expected 30-year precessional cycle and provide insights into the moons' Cassini States. I will describe the latest results and discuss new scientific prospects associated with these observations. First, the spin state can reveal the presence of a subsurface ocean: a decoupling between the icy shell and the interior results in a different obliquity than that of a solid body. Second, an angular deviation from the strict Cassini state enables estimates of energy dissipation. Third, a measurement of librations, if detectable, would enable a measurement of the shell's moment of inertia and provide bounds on the rheology and thickness of the shell. Fourth, the obliquity may explain remarkable surface features, such as the distribution and orientation of cycloids, strike-slip faults, and lineaments on Europa. Fifth, knowledge of the obliquity is required to enable tidal heating calculations. Finally, these measurements are expected to facilitate Clipper and JUICE operations and prevent initial, large mapping errors in spacecraft data products.
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- Award ID(s):
- 2408493
- PAR ID:
- 10588752
- Publisher / Repository:
- EGU
- Date Published:
- Format(s):
- Medium: X
- Institution:
- UCLA
- Sponsoring Org:
- National Science Foundation
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