Magnetic signatures of a tenuous atmosphere at Dione

• Published in: Geophysical research letters Vol. 38; no. 15
• Main Authors: Simon, Sven, Saur, Joachim, Neubauer, Fritz M., Wennmacher, Alexandre, Dougherty, Michele K.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01-08-2011; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Atmosphere; Atmospheric sciences; Cassini; Dione; Earth sciences; Earth, ocean, space; Exact sciences and technology; Magnetic fields; Magnetism; Moon-magnetosphere interactions; Moons; Planetology; Planets; Saturn; sputtering-generated atmosphere; transient radiation belt; atmosphere; models; magnetic field; detection; Saturn; Moon; L shell; Space remote sensing; Radiation belt; Satellite observation; asymmetry; aluminum; Perturbation; Column density; trajectory; Dione; icy satellites; magnetosphere; transient phenomena
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2011GL048454

We present Cassini magnetic field observations from the only two close flybys (16DI and 129DI) of Saturn's icy satellite Dione which have been carried out so far. Data from 16DI show a weak field perturbation in the upstream region, indicative of a tenuous atmosphere around the satellite. By applying an analytical model of the perturbations caused by subalfvénic atmosphere‐magnetosphere interactions, we demonstrate that an atmospheric column density of approximately 1 · 1017 m−2 would be able to sustain the observed field signature. Magnetic field data from 16DI also contain hints that Dione's gas envelope might possess a slight asymmetry between the Saturn‐facing and the Saturn‐averted hemisphere. The detection of a thin atmosphere at Dione might be correlated to the occurrence of a transient radiation belt near the moon's L‐shell at the time of the 16DI flyby, as reported by Roussos et al. (2008b). On the other hand, magnetic field observations from the subsequent downstream encounter 129DI show no clear evidence of an atmosphere, probably due to the flyby trajectory being unsuitable for the detection of the associated perturbations.
Key Points
MAG data from Dione are consistent with the existence of a thin atmosphere
The atmospheric column density is on the order of 1017/m2
The atmosphere might possess a slight hemispheric asymmetry