Publication Date:
2019
Description:
Abstract
In 2017 the Cassini Orbiter made the first in situ measurements of the upper atmosphere and ionosphere of Saturn. The Ion and Neutral Mass Spectrometer (INMS) in its ion mode measured densities of light ion species (H+, H2+, H3+, He+) and the Radio and Plasma Wave Science (RPWS) instrument measured electron densities. During proximal orbit 287 (denoted P287), Cassini reached down to an altitude of about 3000 km above the 1 bar atmospheric pressure level. The topside ionosphere plasma densities measured for P287 were consistent with ionospheric measurements during other proximal orbits. Spacecraft potentials were measured by the RPWS Langmuir probe (LP) and are typically about negative 0.3 Volt. Also, for this one orbit, INMS was operated in an instrument mode allowing the energies of incident H+ ions to be measured. H+ is the major ion species in the topside ionosphere. Ion flow speeds relative to Saturn's atmosphere were determined. In the southern hemisphere, including near closest approach, the measured ion speeds were close to zero relative to Saturn's co‐rotating atmosphere, but for northern latitudes, southward ion flow of about 3 km/s was observed. One possible interpretation is that the ring shadowing of the southern hemisphere sets up an interhemispheric plasma pressure gradient driving this flow.
Print ISSN:
2169-9380
Electronic ISSN:
2169-9402
Topics:
Geosciences
,
Physics
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