A study of the structure and dynamics of Saturn's inner plasma disk
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
This thesis presents a study of the inner plasma disk of Saturn. The results are derived from measurements by the instruments on board the Cassini spacecraft, mainly the Cassini Langmuir probe (LP), which has been in orbit around Saturn since 2004. One of the great discoveries of the Cassini spacecraft is that the Saturnian moon Enceladus, located at 3.95 Saturn radii (1 RS = 60,268 km), constantly expels water vapor and condensed water from ridges and troughs located in its south polar region. Impact ionization and photoionization of the water molecules, and subsequent transport, creates a plasma disk around the orbit of Enceladus. The plasma disk ion components are mainly hydrogen ions H+ and water group ions W+ (O+, OH+, H2O+, and H3O+). The Cassini LP is used to measure the properties of the plasma. A new method to derive ion density and ion velocity from Langmuir probe measurements has been developed. The estimated LP statistics are used to derive the extension of the plasma disk, which show plasma densities above ~20 cm-3 in between 2.7 and 8.8 RS. The densities also show a very variable plasma disk, varying with one order of magnitude at the inner part of the disk. We show that the density variation could partly be explained by a dayside/nightside asymmetry in both equatorial ion densities and azimuthal ion velocities. The asymmetry is suggested to be due to the particle orbits being shifted towards the Sun that in turn would cause the whole plasma disk to be shifted. We also investigate the ion loss processes of the inner plasma disk and conclude that loss by transport dominates loss by recombination in the entire region. However, loss by recombination is still important in the region closest to Enceladus (~±0.5 RS) where it differs with only a factor of two from ion transport loss.
Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 53 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1298
Planetary magnetospheres, Saturn, magnetospheric dynamics, Saturn's inner plasma disk, ring plasma, ion densities, ion velocities, dayside/nightside asymmetry, ion loss rates, Cassini, Langmuir probe, RPWS
Fusion, Plasma and Space Physics
Research subject Space Physics
IdentifiersURN: urn:nbn:se:uu:diva-263278ISBN: 978-91-554-9353-0OAI: oai:DiVA.org:uu-263278DiVA: diva2:858073
2015-11-19, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Cravens, Thomas, Professor
Wahlund, Jan-Erik, Associate professorPiskunov, Nikolai, ProfessorRatynskaia, Svetlana, Professor
FunderSwedish National Space Board
List of papers