P52A-01 INVITED

Magnetospheric interaction with Saturn's icy satellites

Mitchell, D G (donald.g.mitchell@jhuapl.edu) , Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States
* Paranicas, C (chris.paranicas@jhuapl.edu) , Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States
Krimigis, S M (Tom.Krimigis@jhuapl.edu) , Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States
Dougherty, M (m.dougherty@ic.ac.uk) , Imperial College, Blackett Lab, London, SW72BZ United Kingdom
Young, D (dyoung@swri.org) , Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78228 United States
Crary, F (fcrary@swri.org) , Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78228 United States
Kurth, W S (william-kurth@uiowa.edu) , University of Iowa, 210 Van Allen Hall, Iowa City, IA 52242 United States
Gurnett, D A (donald-gurnett@uiowa.edu) , University of Iowa, 210 Van Allen Hall, Iowa City, IA 52242 United States
Hansen, K C (kenhan@umich.edu) , University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109 United States
Kempf, S (sascha-kempf@mpi-hd.mpg.de) , Max Planck Institut fuer Kernphysik, P. O. Box 103980, Heidelberg, 69029 Germany
Srama, R (srama@mpi-hd.mpg.de) , Max Planck Institut fuer Kernphysik, P. O. Box 103980, Heidelberg, 69029 Germany
Team, M (donald.g.mitchell@jhuapl.edu) , Applied Physics Lab, 11100 Johns Hopkins Rd., Laurel, MD 20723 United States

Despite their small size and lack of bound atmospheres, data obtained by the Cassini spacecraft suggest Saturn's icy moons strongly modify the magnetosphere. Analyses of Pioneer and Voyager data have indicated that the moons, for instance, strongly absorb energetic charged particles, with differential rates by species and energy. What was not previously appreciated was the extent to which gas and dust associated with the moons (especially Enceladus) act as a source of magnetospheric plasma and act as a sink for energetic ions. These processes have created a depleted, time variable, patchy inner magnetosphere in some charged particle species. Furthermore, the radiation belts of Saturn are relatively weak compared with Earth and Jupiter. Data taken near Enceladus have revealed a much stronger interaction between that satellite and the corotating magnetic field than had been anticipated -- suggesting a major source of gas and dust. Because in our new view the moons so strongly control the charged particle contents of the magnetosphere, there is an important feedback loop between the characteristics of their surfaces and the magnetosphere. This paper will review some of these effects, and discuss some new insights into the role of the icy moons in Saturn's magnetosphere.

P52A-02 INVITED

Titan's Interaction With its Plasma Environment

* Bertucci, C (c.bertucci@imperial.ac.uk) , Space & Atmospheric Physics Group, Imperial College London, The Blackett Laboratory Prince Consort Road, London, SW72BZ United Kingdom
Neubauer, F M (neubauer@geo.Uni-Koeln.DE) , Institut fur Geophysik und Meteorologie, University of Cologne Albertus-Magnus-Platz, Cologne, 50931 Germany
Law, A (alexandra.law@imperial.ac.uk) , Space & Atmospheric Physics Group, Imperial College London, The Blackett Laboratory Prince Consort Road, London, SW72BZ United Kingdom
Dougherty, M K (m.dougherty@imperial.ac.uk) , Space & Atmospheric Physics Group, Imperial College London, The Blackett Laboratory Prince Consort Road, London, SW72BZ United Kingdom
Dougherty, M K (m.dougherty@imperial.ac.uk) , Swedish Insitute of Space Physics, ngströmlaboratoriet, Lägerhyddsv. 1, Uppsala, SE-751 21 Sweden
Wahlund, J (jwe@irfu.se) , Swedish Insitute of Space Physics, ngströmlaboratoriet, Lägerhyddsv. 1, Uppsala, SE-751 21 Sweden
Szego, K (szego@rmki.kfki.hu) , KFKI Research Institute for Particle and Nuclear Physics, 29-33 Konkoly Thege street, Budapest, H-1121 Hungary
Coates, A (ajc@mssl.ucl.ac.uk) , Mullard Space Science Laboratory, Holmbury St. Mary, Surrey, RH5 6NT United Kingdom
Young, D (dyoung@swri.edu) , Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78228-0510 United States
Arridge, C S (christopher.arridge@imperial.ac.uk) , Space & Atmospheric Physics Group, Imperial College London, The Blackett Laboratory Prince Consort Road, London, SW72BZ United Kingdom
Russell, C T (ctrussell@igpp.ucla.edu) , Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90024-1 United States
Achilleos, N (n.achilleos@imperial.ac.uk) , Space & Atmospheric Physics Group, Imperial College London, The Blackett Laboratory Prince Consort Road, London, SW72BZ United Kingdom

Titan is perhaps one of the most outstanding laboratories in the solar system to study the interaction of the atmosphere of a weakly magnetized body with a wind of plasma. This is mainly due to the variability of the upstream conditions (especially the variation in the angle between the co-rotational flow and the solar EUV radiation direction) as Titan orbits around Saturn inside the Kronian magnetosphere. In this presentation we study the main features characterizing Titan's plasma environment as seen by the plasma instruments onboard the Cassini Spacecraft. These measurements confirm the presence of a well-defined magnetic tail formed by highly draped magnetic fields that pile up on the upstream side as they become strongly mass loaded with colder and heavier plasma from Titan and the absence of a significant intrinsic dynamo-type magnetic field. This 'induced' magnetosphere has a well-defined external boundary characterized by strong enhancements of the magnetic field draping and pileup and followed by important changes in the dominant plasma population which are attributed to the increasing influence of Titan's exosphere. This boundary is characterized by strong rotations in the magnetic field that yield very well defined normal vectors which are usually perpendicular to the draped field. This sudden change in the topology of the magnetic field strongly alters the dynamics of the plasma around Titan. In particular, we compare these features with the very first observations obtained upstream from Titan during the T8 flyby.

P52A-03

Plasma Composition Near Enceladus

* Goldstein, R (rgoldstein@swri.edu) , Southwest Research Institute, 6223 Culebra Road, San Antonio, TX 78238 United States
Berthelier, J (jean-jacques.berthelier@cetp.ipsl.fr) , CETP/IPSL/CNRS, 4 Ave. Neptune, St. Maur, 94100 France
Bouhram, M (mehdi.bouhram@cetp.ipsl.fr) , CETP/IPSL/CNRS, 4 Ave. Neptune, St. Maur, 94100 France
Coates, A J (ajc@mssl.ucl.ac.uk) , Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT United Kingdom
Crary, F J (fcrary@swri.edu) , Southwest Research Institute, 6223 Culebra Road, San Antonio, TX 78238 United States
Eviatar, A (arkee1@daphne.tau.ac.il) , Tel Aviv University, Dept. of Geophysics and Planetary Science, Ramat Aviv, 69978 Israel
Huebner, W F (whuebner@swri.edu) , Southwest Research Institute, 6223 Culebra Road, San Antonio, TX 78238 United States
Shapirio, M (Mark.D.Shappirio@nasa.gov) , NASA Goddard Space Flight Center, MC692, Greenbelt, MD 20771 United States
Smith, H T (hts4f@cms.mail.virginia.edu) , The University of Virginia, Thornton Hall, Charlottesville, VA 22904 United States
Young, D T (dyoung@swri.edu) , Southwest Research Institute, 6223 Culebra Road, San Antonio, TX 78238 United States

During the first year of its orbital tour of Saturn the Cassini spacecraft has performed two close flybys of the icy satellite Enceladus: on March 9, 2005 (504 km closest approach altitude at 6.6 km/s) and July 14, 2005 (172 km altitude at 8.2 km/s). The Cassini Plasma Spectrometer (CAPS) on board the spacecraft measured plasma ion composition (among other things) in the vicinity of Enceladus during these flybys. The primary constituents observed are the so-called water group ions, presumably the result of various electron impact, ion-molecule and solar UV induced reactions with water vapor evolved from icy surfaces. We also identify O2$^{+}$, C$^{+}$, and N$^{+}$. We will discuss some of the probable chemical processes involved and hazard some thoughts about the source of the water vapor. We will also discuss how this watery environment is more dissimilar than similar to a cometary coma.

P52A-04

The Dynamic Atmosphere of Enceladus Revealed by Magnetometer Observations

* Khurana, K K (kkhurana@igpp.ucla.edu) , Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095 United States
Dougherty, M K , Imperial College, Department of Physics, London, SW72AZ United Kingdom
Travnicek, P , Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, 4 Czech Republic
Neubauer, F M , Institute fur Geophysik und Meterologie, University of Cologne, Cologne, 50374 Germany
Saur, J , Institute fur Geophysik und Meterologie, University of Cologne, Cologne, 50374 Germany
Russell, C T , Institute of Geophysics and Planetary Physics, UCLA, Los Angeles, CA 90095 United States

The three close flybys of Enceladus in 2005 by Cassini have provided a wealth of new information on the interaction of Enceladus with the Saturnian magnetospheric plasma. These flybys show that the tiny icy moon (radius 250 km) presents itself as a large obstacle to the plasma flow. All three Enceladus encounters occurred on the upstream side of Enceladus at closest approach distances of 5.8, 3.0 and 1.7 Enceladus radii (RE) respectively. Because Enceladus is located very close to the equatorial plane of Saturn, the plasma density of the corotating Saturnian plasma is quite high and exceeds 60 ions/cm3. The three flybys show that the obstacle is not co-located with Enceladus but is displaced at least one RE south of Enceladus. Further modeling of the signature reveals that the effective obstacle is at least 2 RE in radius and its characteristics (size, conductivity and location) show variations between passes. These results can be modeled using an effective conductivity arising from a plume generated dynamic atmosphere which is confined mainly to the southern hemisphere of Enceladus. The results of the modeling study will be interpreted in context with the observations of the neutral atmosphere obtained from the remote sensing instruments during the E11 flyby.

P52A-05

Magnetospheric Electrons as a Source of Titan's Ionosphere: Model Comparisons with Cassini Data

* Cravens, T E (cravens@ku.edu) , University of Kansas, Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045 United States
Robertson, I P (robertin@ku.edu) , University of Kansas, Department of Physics and Astronomy, University of Kansas, Lawrence, KS 66045 United States
Keller, C N (charles_n_keller@cornerstone.edu) , Cornerstone University, Cornerstone University, Dept. of Physical Sciences, Cornerstone Univ., Grand Rapids, MI 49505 United States
Waite, J H (hunterw@umich.edu) , University of Michigan, Dept. of Atmospheric, Oceanic, and Space Sciences, 2455 Hayward, University of Michigan, Ann Arbor, MI 48109-2143 United States
Kasprzak, W T (wayne.kascprzak@gsfc.nasa.gov) , NASA Goddard Space Flight Center, NASA Goddard Space Flight Center, Greenbelt, MD 20771 United States
Niemann, H B (Hasso.Niemann@gsfc.nasa.gov) , NASA Goddard Space Flight Center, NASA Goddard Space Flight Center, Greenbelt, MD 20771 United States
Yelle, R V (yelle@lpl.arizona.edu) , University of Arizona, Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721-0092 United States
Luhmann, J G (jgluhman@sunspot.ssl.berkeley.edu) , University of California Berkeley, Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
Ledvina, S (ledvina@ssl.berkeley.edu) , University of California Berkeley, Space Sciences Laboratory, University of California, Berkeley, CA 94720 United States
McNutt, R L (ralph_mcnutt@jhuapl.edu) , Applied Physics Laboratory, Johns Hopkins University, Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723 United States
Ip, W (wingip@astro.ncu.edu.tw) , National Central University, National Central University Taiwan, Chung-Li, 32054 Taiwan
De La Haye, V (vdelah@engin.umich.edu) , University of Michigan, Dept. of Atmospheric, Oceanic, and Space Sciences, 2455 Hayward, University of Michigan, Ann Arbor, MI 48109-2143 United States
Müller-Wordag, I (i.Muellerwodarg@imperial.ac.uk) , Imperial College, Space and Atmospheric Physics Group, Imperial College, London, SW7 2BW United Kingdom
Coates, A J (ajc@mssl.ucl.ac.uk) , University College London, Mullard Space Science Laboratory Holmbury St Mary, Dorking, Surrey RH5 6NT,, Holmbury St Mary, RH5 6NT United Kingdom

The Cassini Ion and Neutral Mass Spectrometer (INMS) onboard the Cassini Orbiter measured the neutral composition and structure of the upper atmosphere during 3 encounters. The INMS measured the ionospheric composition only on the outbound leg of the T5 pass, when the spacecraft was on the nightside. Possible ionization sources for this nightside ionosphere include transport from the dayside, or (more likely) electron impact ionization associated with precipitation of magnetospheric electrons. We use a model of Titan's ionosphere, which includes ion chemistry, suprathermal electron transport, and electron energetics to investigate how the ionosphere responds to magnetospheric inputs. In particular, model results seem to suggest that magnetospheric electrons with energies between about 25 eV and 800 eV are needed to explain the ion density profiles measured by the INMS. The model is also used to interpret the ion composition seen by the INMS and to test the ion chemistry scheme used.

P52A-06

The Polar Wind as a Mass Source for Saturn's Magnetosphere

* Glocer, A (aglocer@umich.edu) , University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
Gombosi, T (tamas@umich.edu) , University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
Toth, G (gtoth@umich.edu) , University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
Hansen, K (kenhan@umich.edu) , University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109-2143 United States
Ridley, A (ridley@umich.edu) , University of Michigan, 2455 Hayward St., Ann Arbor, MI 48109-2143 United States

Characterizing the relative importance of the various mass sources is crucial to understanding Saturn's magnetosphere. Most research in this area focuses on the addition of mass from the icy satellites and rings. Comparatively little attention has been paid to the ionospheric source. Our study addresses this issue by using multi-fluid numerical simulations of Saturn's polar wind to determine the magnitude of the contribution. We introduce a model capable of calculating the polar wind at Earth and Saturn, solving the gyrotropic transport equations. The polar wind at Saturn is calculated from below the peak ionospheric density to an altitude of one Saturn radius, giving fluxes for $H_{3}^{+}$, $H^{+}$, and electrons. Similarly, at Earth the calculation ranges from 200 km to approximately one Earth radius, providing fluxes for $O^{+}$, $H^{+}$, and $He^{+}$. We calculate source rates for various atmospheric profiles, and compare the results with those calculated from other models and measurements where appropriate.

P52A-07

Suprathermal Heavy Ion Observations During the Titan-5 Close Flyby

* Hamilton, D C (dch@umd.edu) , University of Maryland, Department of Physics, College Park, MD 20742 United States
Garnier, P (Philippe.Garnier@cesr.fr) , Centre D'Etude Spatiale Des Rayonnements, 9 Avenue du Colonel Roche, Toulouse, 31028 France
Dandouras, I (Iannis.Dandouras@cesr.fr) , Centre D'Etude Spatiale Des Rayonnements, 9 Avenue du Colonel Roche, Toulouse, 31028 France
Krimigis, S M (tom.krimigis@jhuapl.edu) , Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 United States
Mitchell, D G (donald.g.mitchell@jhuapl.edu) , Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 United States

The Charge-Energy-Mass Spectrometer (CHEMS), one of three sensors comprising the MIMI investigation on Cassini, measures the mass and charge state of ions in the energy per charge range 3--220 keV/e. During Titan-5, Cassini's fifth close flyby of Titan on day 106, 2005, CHEMS observed an anisotropic flux of heavy ions during a 10-minute period beginning about 1915 UT, 3 minutes after closest approach. The measured ion masses ranged from 14--30 amu. Their energy spectrum exhibited a sharp cutoff above 12 keV. These ions are presumably pickup ions from Titan. We will discuss their composition, anisotropy, and energy spectrum in terms of acceleration by the corotation electric field.

Author(s) (2005), Title, Eos Trans. AGU, 86(52), Fall Meet. Suppl., Abstract #####-##.