Improved Determination of Europa's Long‐Wavelength Topography Using Stellar Occultations. Issue 7 (23rd July 2021)

• Record Type: Journal Article
• Authors: Abrahams, Jacob N. H.; Nimmo, Francis; Becker, Tracy M.; Gladstone, G. Randall; Retherford, Kurt D.; Steinbrügge, Gregor; Mazarico, Erwan
• Is Part Of: Earth and space science. Volume 8:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-23
• Subjects: altimetry -- clipper -- Europa -- geodesy -- geophysics -- interiors; Space sciences -- Periodicals; Geophysics -- Periodicals; 500.5
• DOI: 10.1029/2020EA001586
• Languages: English
• ISSNs: 2333-5084

Abstract

Abstract: Europa Clipper will arrive at Jupiter at the end of this decade and will explore Europa through a series of flybys. One of its many goals is to characterize Europa's topography and global shape using the Europa Imaging System and Radar for Europa Assessment and Sounding: Ocean to Near‐surface (REASON) instruments. In addition, Europa Clipper's UV Spectrograph will observe stars pass behind (be occulted by) Europa. The spectrograph has sufficiently precise timing, corresponding to a topographic precision of order meters, that these occultations can also serve as altimetric measurements. Because of gaps in the REASON radar altimeter coverage imposed by the flyby geometries, the addition of ∼100 occultations results in a substantial improvement in the recovery of Europa's long‐wavelength shape. Typically, five extra spherical harmonic degrees of topography can be recovered by combining occultations with radar altimetry. Plain Language Summary: Understanding Europa's topography is crucial to understand the moon for a variety of reasons. One way to quantify the topography is global shape, where we describe the entire surface at once. For example, Earth's rotation causes it to bulge at the equator, and we can describe that bulge with a single number: Earth is on average about 40 km larger at the equator than at the poles. A body's global shape as a whole can be described in a similar way, with a series of amplitudes of prescribed shapes (like an equatorial bulge) referred to as "spherical harmonics." Understanding global shape is important because the ice shell is an inherently global structure, and its history, strength, and behavior often reveal themselves as global features. However, if there are gaps in data coverage, spherical harmonics with features (approximately) smaller than those gaps become unreliable to fit, limiting the resolution of shape models. In this paper, we show that measurements by Europa Clipper's UV Spectrograph of stars passing behind Europa can help to fill gaps in Europa Clipper's topographic coverage and significantly improve our ability to determine Europa's global shape. Key Points: Understanding Europa's global shape is important for understanding its ice shell Europa Clipper's primary instruments for measuring topography will be limited in constraining global shape because Clipper orbits Jupiter Stellar Occultations obtained by Europa‐UVS can help fill in the gaps in altimetric coverage, significantly improving global shape fits