Universität zu Köln

Hartkorn, Oliver and Saur, Joachim ORCID: 0000-0003-1413-1231 (2017). Induction signals from Callisto's ionosphere and their implications on a possible subsurface ocean. J. Geophys. Res-Space Phys., 122 (11). S. 11677 - 11698. WASHINGTON: AMER GEOPHYSICAL UNION. ISSN 2169-9402

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Abstract

We investigate whether induction within Callisto's electrically conductive ionosphere can explain observed magnetic fields which have previously been interpreted as evidence of induction in a saline, electrically conductive subsurface ocean. Callisto's ionosphere is subject to the flow of time-periodic magnetized plasma of Jupiter's magnetosphere, which induces electric fields and electric currents in Callisto's electrically conductive ionosphere. We develop a simple analytic model for a first quantitative understanding of the effects of induction in Callisto's ionosphere caused by the interaction with a time-variable magnetic field environment. With this model, we also investigate how the associated ionospheric currents close in the ambient magnetospheric plasma. Based on our model, we find that the anisotropic nature of Callisto's ionospheric conductivity generates an enhancement effect on ionospheric loop currents which are driven by the time-variable magnetic field. This effect is similar to the Cowling channel effect known from Earth's ionosphere. Subsequently, we numerically calculate the expected induced magnetic fields due to Jupiter's time-variable magnetic field in an anisotropic conductive ionosphere and compare our results with the Galileo C-3 and C-9 flybys. We find that induction within Callisto's ionosphere is responsible for a significant part of the observed magnetic fields. Ionospheric induction creates induced magnetic fields to some extent similar as expected from a subsurface water ocean. Depending on currently unknown properties such as Callisto's nightside ionosphere, the existence of layers of dirty ice and the details of the plasma interaction, a water ocean might be located much deeper than previously thought or might not exist at all.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Hartkorn, Oliver UNSPECIFIED UNSPECIFIED UNSPECIFIED Saur, Joachim UNSPECIFIED orcid.org/0000-0003-1413-1231 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-213474
DOI:	10.1002/2017JA024269
Journal or Publication Title:	J. Geophys. Res-Space Phys.
Volume:	122
Number:	11
Page Range:	S. 11677 - 11698
Date:	2017
Publisher:	AMER GEOPHYSICAL UNION
Place of Publication:	WASHINGTON
ISSN:	2169-9402
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language HUBBLE-SPACE-TELESCOPE; JOVIAN MAGNETOSPHERE; PLASMA INTERACTION; UNIPOLAR INDUCTOR; CARBON-DIOXIDE; IO PLASMA; EUROPA; ATMOSPHERE; FIELD; CONDUCTIVITY Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/21347