Universität zu Köln

Alday, Juan ORCID: 0000-0003-1459-3444, Roth, Lorenz, Ivchenko, Nickolay ORCID: 0000-0003-2422-5426, Retherford, Kurt D., Becker, Tracy M., Molyneux, Philippa and Saur, Joachim ORCID: 0000-0003-1413-1231 (2017). New constraints on Ganymede's hydrogen corona: Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 2014. Planet Space Sci., 148. S. 35 - 45. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD. ISSN 0032-0633

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Abstract

Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Alday, Juan UNSPECIFIED orcid.org/0000-0003-1459-3444 UNSPECIFIED Roth, Lorenz UNSPECIFIED UNSPECIFIED UNSPECIFIED Ivchenko, Nickolay UNSPECIFIED orcid.org/0000-0003-2422-5426 UNSPECIFIED Retherford, Kurt D. UNSPECIFIED UNSPECIFIED UNSPECIFIED Becker, Tracy M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Molyneux, Philippa UNSPECIFIED UNSPECIFIED UNSPECIFIED Saur, Joachim UNSPECIFIED orcid.org/0000-0003-1413-1231 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-211183
DOI:	10.1016/j.pss.2017.10.006
Journal or Publication Title:	Planet Space Sci.
Volume:	148
Page Range:	S. 35 - 45
Date:	2017
Publisher:	PERGAMON-ELSEVIER SCIENCE LTD
Place of Publication:	OXFORD
ISSN:	0032-0633
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language GALILEAN SATELLITES; OXYGEN ATMOSPHERE; ATOMIC-HYDROGEN; LINE-PROFILE; WATER-VAPOR; ULTRAVIOLET; AURORA; MODEL; EXOSPHERES; EXCITATION Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/21118