Universität zu Köln

Saur, Joachim ORCID: 0000-0003-1413-1231, Duling, Stefan, Roth, Lorenz, Jia, Xianzhe ORCID: 0000-0002-8685-1484, Strobel, Darrell F., Feldman, Paul D., Christensen, Ulrich R., Retherford, Kurt D., McGrath, Melissa A., Musacchio, Fabrizio, Wennmacher, Alexandre, Neubauer, Fritz M., Simon, Sven ORCID: 0000-0002-6204-5437 and Hartkorn, Oliver (2015). The search for a subsurface ocean in Ganymede with Hubble Space Telescope observations of its auroral ovals. J. Geophys. Res-Space Phys., 120 (3). S. 1715 - 1738. WASHINGTON: AMER GEOPHYSICAL UNION. ISSN 2169-9402

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Abstract

We present a new approach to search for a subsurface ocean within Ganymede through observations and modeling of the dynamics of its auroral ovals. The locations of the auroral ovals oscillate due to Jupiter's time-varying magnetospheric field seen in the rest frame of Ganymede. If an electrically conductive ocean is present, the external time-varying magnetic field is reduced due to induction within the ocean and the oscillation amplitude of the ovals decreases. Hubble Space Telescope (HST) observations show that the locations of the ovals oscillate on average by 2.0 degrees 1.3 degrees. Our model calculations predict a significantly stronger oscillation by 5.8 degrees 1.3 degrees without ocean compared to 2.2 degrees 1.3 degrees if an ocean is present. Because the ocean and the no-ocean hypotheses cannot be separated by simple visual inspection of individual HST images, we apply a statistical analysis including a Monte Carlo test to also address the uncertainty caused by the patchiness of observed emissions. The observations require a minimum electrical conductivity of 0.09 S/m for an ocean assumed to be located between 150 km and 250 km depth or alternatively a maximum depth of the top of the ocean at 330 km. Our analysis implies that Ganymede's dynamo possesses an outstandingly low quadrupole-to-dipole moment ratio. The new technique applied here is suited to probe the interior of other planetary bodies by monitoring their auroral response to time-varying magnetic fields.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Saur, Joachim UNSPECIFIED orcid.org/0000-0003-1413-1231 UNSPECIFIED Duling, Stefan UNSPECIFIED UNSPECIFIED UNSPECIFIED Roth, Lorenz UNSPECIFIED UNSPECIFIED UNSPECIFIED Jia, Xianzhe UNSPECIFIED orcid.org/0000-0002-8685-1484 UNSPECIFIED Strobel, Darrell F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Feldman, Paul D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Christensen, Ulrich R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Retherford, Kurt D. UNSPECIFIED UNSPECIFIED UNSPECIFIED McGrath, Melissa A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Musacchio, Fabrizio UNSPECIFIED UNSPECIFIED UNSPECIFIED Wennmacher, Alexandre UNSPECIFIED UNSPECIFIED UNSPECIFIED Neubauer, Fritz M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Simon, Sven UNSPECIFIED orcid.org/0000-0002-6204-5437 UNSPECIFIED Hartkorn, Oliver UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-405485
DOI:	10.1002/2014JA020778
Journal or Publication Title:	J. Geophys. Res-Space Phys.
Volume:	120
Number:	3
Page Range:	S. 1715 - 1738
Date:	2015
Publisher:	AMER GEOPHYSICAL UNION
Place of Publication:	WASHINGTON
ISSN:	2169-9402
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language MAGNETIC-FIELD; JOVIAN MAGNETOSPHERE; INTERNAL STRUCTURE; CONSTRAINTS; EUROPA; CALLISTO; MODELS; SATELLITES; ATMOSPHERE; MORPHOLOGY Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/40548