Constraining Europa’s Global Shape with Stellar Occultations Collected by Europa Clipper’s UV Spectrograph

Abstract:

One of Europa Clipper’s many scientific objectives is to understand Europa’s ice shell structure [1], and a major way to constrain that structure is by measuring Europa’s long wavelength (large-scale) shape [2]. The primary instrument that Europa Clipper will use to study Europa’s ice shell is its radar instrument REASON [3,4]. However, because the spacecraft will orbit Jupiter (not Europa) and will only encounter Europa during flybys, it is not possible to obtain complete global coverage with the radar altimetry alone. In this work, we explore whether Europa Clipper’s Ultraviolet Spectrograph (Europa-UVS) is able to provide additional constraints which can enable higher quality fits to Europa’s global shape. Specifically, Europa-UVS stellar occultation observations can serve as altimetric measurements with very high precision (of order 1 meter), and their spatial distribution means they can serve as a complementary dataset to radar altimetry. We show that by combining radar altimetry with occultation data, our fits to Europa’s global shape become more precise and can be extended to shorter length scales (an improvement of ~5 spherical harmonic degrees), allowing a more detailed characterization of Europa’s global ice shell structure. However, the addition of the UVS occultations is not sufficient for detecting Europa tidal deformation.

[1] Pappalardo, R. T., et al. (2019) AGU P53B–06.

[2] Nimmo, F., et al. (2007) Icarus.

[3] Blankenship, D., (2018) COSPAR B5.3–55–18.

[4] Steinbruegge, G., et al. (2018) EPSL.