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Measuring Ganymede's Librations with Laser Altimetry

Steinbrügge, Gregor and Steinke, Teresa and Thor, Robin and Stark, Alexander and Hussmann, Hauke (2019) Measuring Ganymede's Librations with Laser Altimetry. Geosciences, 9 (7), p. 320. MDPI (Multidisciplinary Digital Publishing Institute). DOI: 10.3390/geosciences9070320 ISSN 2076-3263

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Abstract

Jupiter’s moon Ganymede might be in possession of a subsurface ocean located between two ice layers. However, from Galileo data it is not possible to unambiguously infer the thickness and densities of the individual layers. The upcoming icy satellite mission JUICE (JUpiter ICy moonsExplorer) will have the possibility to perform more detailed investigations of Ganymede’s interior structure with the radio science experiment 3GM and the GAnymede Laser Altimeter (GALA). Here we investigate the possibility to derive the rotational state of the outer ice shell by using topography measured by laser altimetry. We discuss two different methods to invert synthetic laseraltimetry data. Method 1 is based on a spherical harmonics expansion and Method 2 solves for B-splines on a rectangular grid. While Method 1 has significant limitations due to the omission of high degrees of the global expansion, Method 2 leads to stable results allowing for an estimate of the in-orbit measurement accuracy. We estimate that GALA can measure the amplitude of Ganymede’s librations with an accuracy of 2.5–6.6 μrad (6.6–17.4 m at the equator). This allows for determining the thickness of an elastic ice shell, if decoupled from the deeper interior by a subsurface ocean, to about an accuracy of 24–65 km.

Item URL in elib:https://elib.dlr.de/132293/
Document Type:Article
Title:Measuring Ganymede's Librations with Laser Altimetry
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Steinbrügge, GregorInstitute for Geophysics, University of Texas at Austin, USAUNSPECIFIED
Steinke, TeresaUniversity of DelftUNSPECIFIED
Thor, RobinMax Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, GermanyUNSPECIFIED
Stark, Alexanderalexander.stark (at) dlr.dehttps://orcid.org/0000-0001-9110-1138
Hussmann, Haukehauke.Hussmann (at) dlr.deUNSPECIFIED
Date:20 July 2019
Journal or Publication Title:Geosciences
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:9
DOI :10.3390/geosciences9070320
Page Range:p. 320
Publisher:MDPI (Multidisciplinary Digital Publishing Institute)
ISSN:2076-3263
Status:Published
Keywords:Ganymede, GALA, JUICE, Laser Altimetry, Rotation, Libration
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):Project JUICE JANUS and GALA
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Geodesy
Deposited By: Stark, Alexander
Deposited On:09 Dec 2019 15:32
Last Modified:14 Dec 2019 04:24

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