P41B-01 08:00h

Cassini Imaging Observations of Titan

* McEwen, A (mcewen@pirl.lpl.arizona.edu) , LPL, U. Arizona, Sonett Space Sciences, Tucson, 85721
West, R (Robert.A.West@jpl.nasa.gov) , Jet Propulsion Lab, 4800 Oak Grove Dr., Pasadena, 91109
Turtle, E (turtle@pirl.lpl.arizona.edu) , LPL, U. Arizona, Sonett Space Sciences, Tucson, 85721
Perry, J (perry@pirl.lpl.arizona.edu) , LPL, U. Arizona, Sonett Space Sciences, Tucson, 85721
Johnson, T (Torrence.V.Johnson@jpl.nasa.gov) , Jet Propulsion Lab, 4800 Oak Grove Dr., Pasadena, 91109
DelGenio, A (delgenio@giss.nasa.gov) , NASA GISS, 2880 Broadway, New York, 10025
Dawson, D (dddawson@pirl.lpl.arizona.edu) , LPL, U. Arizona, Sonett Space Sciences, Tucson, 85721
Campbell, S (campbell@lpl.arizona.edu) , LPL, U. Arizona, Sonett Space Sciences, Tucson, 85721
Barbara, J (jbarbara@giss.nasa.gov) , NASA GISS, 2880 Broadway, New York, 10025
Porco, C (carolyn@ciclops.org) , Space Science Inst., 4750 Walnut St., Boulder, 80301

The Cassini ISS team will present preliminary results from new high-resolution images of Titan. ISS can best detect the surface and lower-troposphere clouds though a narrow filter centered in the 940-nm methane window. Near-global coverage acquired during approach to Saturn revealed 100-km-scale dark markings in the equatorial region, some with straight trends or boundaries suggestive of tectonic influences. Cassini passed within 339,000 km of the south-polar region on July 2 and acquired images with scales of 2-3 km/pixel, revealing clouds that change on timescales of a hour or less. The photochemical haze limited resolution of the surface to ~10 km, as predicted (Porco et al., Space Sci. Rev., in press). No evidence for topographic shading was seen, probably because icy satellites tend to have low relief, not detectable at 10-km scales, but the haze scattering must also lower the contrast of any topographic shading. The albedo markings include straight and meandering dark linear features and crudely rectangular or irregular dark and bright patches. There is nothing suggestive of a large impact structure over this ~10% of Titan's surface. Over 4 Ga, comets are expected to produce from 0.6 to 6 impact features > =100 km diameter on 10% of Titan's leading hemisphere (Korycansky and Zahnle, in press, Planet. Space Sci.). If large impact structures are in fact rare on Titan, this would indicate significant endogenic resurfacing since an early period of heavy bombardment. The first close targeted flyby of Titan on October 26 will return much more detailed images (down to ~150 m/pixel) of an equatorial region on the anti-Saturn hemisphere, including the landing site for the Huygens probe; we will present preliminary image products and interpretations.

P41B-02 08:15h

First Cassini RADAR Observations of Titan

* Elachi, C , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Lorenz, R D (rlorenz@lpl.arizona.edu) , LPL, University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721 United States
Anderson, Y , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Boehmer, R , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Callahan, P , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Hamilton, G , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Janssen, M , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Johnson, B , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Kelleher, K , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Lopes, R , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Ostro, S , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Roth, L , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Wall, S , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
West, R , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Hensley, S , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Gim, Y , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Stiles, B , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Schaffer, S , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Shimada, J , Jet Propulsion Laboratory , 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Allison, M , NASA/GISS, 2880 Broadway, New York, NY 10025 United States
Soderblom, L , USGS, 2255 N Gemini Drive, Flagstaff, AZ 86001 United States
Wood, C , PSI, 1700 E. Ft Lowell ST, Tucson, AZ 85719 United States
Posa, F , Politechnico di Bari, Via Amandola 173, Bari, 70126 Italy
Stofan, E , Proxemy Research, 12202 Raritan Lane, Bowie, MD 20715 United States
Zebker, H , Stanford University, 260 Micchell, Stanford, CA 94305 United States
Lunine, J , LPL, University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721 United States
Francescetti, G , University of, Naples, Naples, 80125 Italy
Picardi, G , University of Rome 'La Sapienza', Via Edossiana 18, Rome, 00184 Italy
Seu, R , University of Rome 'La Sapienza', Via Edossiana 18, Rome, 00184 Italy
Muhleman, D , Caltech, GPS, Pasadena, CA 91125 United States
Encrenaz, P , DEMIRM/Obs de Paris, 61, Ave de l'Observatoire, Paris, 75014 France
Kirk, R , NASA/GISS, 2880 Broadway, New York, NY 10025 United States

The Cassini TA flyby with Titan on 26 October 2004 has a closest approach altitude of 1200km, and features several RADAR observations. Shortly before closest approach, the Synthetic Aperture Radar (SAR) mapping mode of the instrument will be used to image a small region (~0.5%) of the surface at around 40o N latitude with a planned resolution of between 0.4 and 2km. Additional observations outbound from Titan include a short altimetry swath, additional scatterometry, and a low-resolution full-disk passive radiometry map. We will present the available results from the initial analysis of the active measurements of this first Titan encounter.

P41B-03 08:30h

Early Results at Titan with the Cassini RADAR Radiometer

Janssen, M A (michael.a.janssen@jpl.nasa.gov) , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
* Lorenz, R D (rlorenz@lpl.arizona.edu) , Lunar and Planetary Laboratory, University of Arizona 1629 E. University Blvd, Tucson, AZ 85721 United States
Anderson, Y Z , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Boehmer, R , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Boehmer, R , Lunar and Planetary Laboratory, University of Arizona 1629 E. University Blvd, Tucson, AZ 85721 United States
Callahan, P , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Kelleher, K , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Lopes, R , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Roth, L , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Wall, S , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
West, R , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
Johnson, B T , Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 United States

The Cassini Radar instrument includes a passive microwave radiometer operating at 13.78 GHz (~ 2.2 cm wavelength). An objective for the radiometer is the global mapping of the temperature and dielectric constant of Titan's surface, to be achieved using raster scans to measure the polarized thermal emission from Titan's disk on selected inbound and outbound passes. Results will be presented from the first such mapping of Titan, to be obtained during the initial Titan pass on 26 August, 2004 and initial interpretations made with regard to composition and temperature distribution. This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

P41B-04 08:45h

INMS Observations of Titan's Upper Atmosphere on 26 OCT 2004

* Yelle, R V (yelle@lpl.arizona.edu) , University of Arizona, 1629 E. University Blvd, Tucson, AZ 85721 United States
Waite, J H , University of Michigan, Space Physics Research Lab 1136 Space Research Bldg, Ann Arbor, MI 48109 United States
Cravens, T E , University of Kansas, 1082 Mallot Hall, Lawrence, KS 66045 United States
Ip, W , National Central University, Institute of Astronomy, Chung Li, AZ 32054 Taiwan
Kasprzak, W , Goddard Space Flight Center, Code 915, Greenbelt, MD 20771 United States
Luhmann, J , University of California, Centennial Drive, Berkeley, CA 94720 United States
McNutt, R , Applied Physics Lab/Johns Hopkins University, 11100 Johns Hopkins RD, Laurel, MD 20723 United States
Ledvina, S , University of California, Centennial Drive, Berkeley, CA 94720 United States
de la Haye, V , University of Michigan, Space Physics Research Lab 1136 Space Research Bldg, Ann Arbor, MI 48109 United States

On 26 October 2004 the Cassini spacecraft makes its first close pass to Titan, passing within approximately 1200 km of the surface. The measurements planned for the Ion Neutral Mass Spectrometer experiment will constitute the first in situ observations of Titan's upper atmosphere. Densities of molecular constituents including N2 and CH4 will be measured as a function of altitude. Analysis of these data will determine the temperature and abundances of the major atmospheric constituents. The abundance of some minor atmospheric constituents may also be determined.

P41B-05 09:00h

Stratospheric composition of Titan from Cassini/CIRS observations

* Coustenis, A (Athena.Coustenis@obspm.fr) , LESIA, Obs. de Paris-Meudon, 5, place Jules Jannsen, Meudon, 92195 France
B\'ezard, B (bruno.bezard@obspm.fr) , LESIA, Obs. de Paris-Meudon, 5, place Jules Jannsen, Meudon, 92195 France
Lellouch, E (emmanuel.lellouch@obspm.fr) , LESIA, Obs. de Paris-Meudon, 5, place Jules Jannsen, Meudon, 92195 France
Fouchet, T (thierry.fouchet@obspm.fr) , LESIA, Obs. de Paris-Meudon, 5, place Jules Jannsen, Meudon, 92195 France
Conrath, B (barney.j.conrath@gsfc.nasa.gov) , CRSR, Cornell University, Ithaca, NY 14853 United States
Achterberg, R K (Richard.K.Achterberg@gsfc.nasa.gov) , SSAI/ Lab. Extrat. Phys., NASA/GSFC Code 693, Greenbelt, MD 20771 United States
Jennings, D E (donald.e.jennings@gsfc.nasa.gov) , NASA/GSFC, Code 693, Greenbelt, MD 20771 United States
Bjoraker, G (gordon.bjoraker@gsfc.nasa.gov) , NASA/GSFC, Code 693, Greenbelt, MD 20771 United States
Flasar, M (f.m.flasar@nasa.gov) , NASA/GSFC, Code 693, Greenbelt, MD 20771 United States

We have analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard Cassini mission during the first Titan fly-by (July 2-3 2004). The spectra characterize essentially regions around Titan's south pole and up to 5 deg S (with higher emission angles) from the emission observed in the 3 CIRS detectors (covering roughly the 10-1500 cm$^{-1}$ spectral range with a 0.53 cm$^{-1}$ apodized resolution). The composite spectrum shows a large variety of molecular signatures : hydrocarbons, nitriles and 3 oxygen components. We have used a temperature profile retrieved by inversion of the emission observed in the methane $\nu_4$ band at 1304 cm-$^{-1}$ and a line-by-line radiative transfer code to infer the abundances of the trace constituents in Titan's stratosphere. We compare these mixing ratios with values retrieved two Titan seasons ago by V1 and V2 IRIS observations and with more recent disk-averaged Infrared Space Observatory (ISO) results.

P41B-06 09:15h

Cassini Magnetic Field Observations During the Close Titan Encounter on October 26, 2004

* Neubauer, F M (fritz.neubauer@t-online.de) , Institute of Geophysics and Meteorology,University of Cologne, Albertus Magnus Platz, Koeln, 50923 Germany
Dougherty, M K (m.dougherty@imperial.ac.uk) , Space and Atmospheric Physics Imperial College London, Prince Consort Road, London, SW7 2AZ United Kingdom
Achilleos, N (n.achilleos@imperial.ac.uk) , Space and Atmospheric Physics Imperial College London, Prince Consort Road, London, SW7 2AZ United Kingdom
Andre, N (Nicolas.Andre@cesr.fr) , CESR, 9 Avenue du Colonel Roche, Toulouse Cedex 4, 31028 France
Arridge, C S (christopher.arridge@imperial.ac.uk) , Space and Atmospheric Physics Imperial College London, Prince Consort Road, London, SW7 2AZ United Kingdom
Bertucci, C (c.bertucci@imperial.ac.uk) , Space and Atmospheric Physics Imperial College London, Prince Consort Road, London, SW7 2AZ United Kingdom
Khurana, K K (kkhurana@igpp.ucla.edu) , University of California Los Angeles, Institute of Geophysics and Planetary Physics, 405 Hilgard Avenue , Los Angeles, 90095-156 United States
Russell, C S (ctrussel@igpp.ucla.edu) , University of California Los Angeles, Institute of Geophysics and Planetary Physics, 405 Hilgard Avenue , Los Angeles, 90095-156 United States
Wennmacher, A (wennmach@geo.Uni-Koeln.DE) , Institute of Geophysics and Meteorology,University of Cologne, Albertus Magnus Platz, Koeln, 50923 Germany

We shall report observations by the Cassini magnetometer experiment during the TA encounter of the Cassini spacecraft on October 26, 2004 with a minimum altitude of 1200 km. This is the first close encounter with Titan after the Voyager 1 flyby of November 12, 1980. Because of the Saturnian local time of 10.6 H, i.e. just before noon, Titan could be found inside the outer magnetosphere of Saturn or less probably in the magnetosheath or with much lower probability even in the solar wind. In the magnetosphere we shall be able to investigate the wake and tail forming region at intermediate northern latitudes on the inbound and northbound flyby trajectory. We shall also study boundaries,draping features etc. In addition we shall look for evidence for a magnetic field of internal origin.

P41B-07 09:30h

Plasma Measurements in Titan's Ionosphere: Initial Cassini/CAPS Results

* Young, D T (dyoung@swri.edu) , Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
Crary, F J (fcrary@swri.edu) , Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
Barragiola, R A (rb9a@virginia.edu) , University of Virginia, Engineering Physics, Thornton Hall, Charlottesville, VA 22904 United States
Barraclough, B L (bbarraclough@lanl.gov) , Los Alamos National laboratory, MS D-446, Los Alamos, NM 87545 United States
Berthelier, J (jean-jacques.berthelier@cetp.ipsl.fr) , Centre d'etude des Environnements Terrestre et Planetaires, 4. Ave. de Neptune, St. Maur des Fosses, 94107 France
Coates, A J (ajc@mssl.ucl.ac.uk) , Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Sur RH5 6NT United Kingdom
Gosling, J T (jgosling@lanl.gov) , Los Alamos National laboratory, MS D-446, Los Alamos, NM 87545 United States
Hill, T W (hill@rice.edu) , Rice University, Physics and Astronomy Dept. MS 108, Houston, TX 77251 United States
Johnson, R E (rej@virginia.edu) , University of Virginia, Engineering Physics, Thornton Hall, Charlottesville, VA 22904 United States
McComas, D J (dmccomas@swri.edu) , Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238 United States
Reisenfeld, D (dan.reisenfeld@umontana.edu) , University of Montana, Department of Physics and Astronomy, 32 Campus Drive, Missoula, MT 59812 United States
Rymer, A M (amr@mssl.ucl.ac.uk) , Goddard Space Flight Center, Greenbelt Road, Greenbelt, MD 20771 United States
Sittler, E C (Edward.C.Sittler@nasa.gov) , Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Sur RH5 6NT United Kingdom
Steinberg, J (jsteinberg@lanl.gov) , Los Alamos National laboratory, MS D-446, Los Alamos, NM 87545 United States
Svenes, K R (ksv@ffi.no) , Norwegian Defense Research Establishment, P.O. Box, Kjeller, N-2027 Norway
Szego, K (szego@rmki.kfki.hu) , KFKI-RMKI, Konkoly Thege Str. 29-33, Budapest, H-1525 Hungary
Vilppola, J (jari.vilppola@oulu.fi) , University of Oulu, Linnamaa, Oulu, F-90014 Finland

On October 26, 2004 the Cassini spacecraft had its first near encounter with Titan at 1250 km altitude. We will present the initial Cassini Plasma Spectrometer (CAPS) measurements of ion and electron fluxes as a function of their direction of arrival over a hemispheric field of view and their energy/charge between 1 eV and 50 keV (ions) and 1 eV and 28 keV (electrons). The CAPS ion mass spectrometer also simultaneously makes time-of-flight measurements of ion mass/charge spectra between 1 and ~ 100 amu. A second ion spectrometer will measure ion velocity distributions with resolution of a few percent. We anticipate that CAPS results will include a sounding of the electron density and ion composition; the ion and electron temperatures down to an altitude of 1250 km; the pitch angle distributions of magnetospheric electrons entering Titan's atmosphere; and the properties of the magnetospheric plasma upstream and in the flanks of the Titan interaction region.

P41B-08 09:45h

VIMS Evidence for Palimpsests on Titan as a Constraint on Widespread Precipitation.

* Nelson, R M (robert.m.nelson@jpl.nasa.gov) , JPL, JPL, Pasadena, CA 91109 United States
Brown, R H (rhb@lpl.arizona.edu) , U. Ariz, LPL, Tucson, AZ 85721 United States
Hapke, B W (hapke@pitt.edu) , U. Pittsburgh, Dept of Geo and Planetary Sci, Pittsburgh, PA 15260 United States
Smythe, W D (wsmythe@lively.jpl.nasa.gov) , JPL, JPL, Pasadena, CA 91109 United States
Kamp, L (lucas.w.kamp@jpl.nasa.gov) , JPL, JPL, Pasadena, CA 91109 United States
Boryta, M (mboryta@oco.net) , Mount SAC, Dept of Geology, Walnut, CA 91109 United States
Baines, K H (kevin.h.baines@jpl.nasa.gov) , JPL, JPL, Pasadena, CA 91109 United States
Giancarlo, B (giancarlo.bellucci@ifsi.rm.cnr.it) , Istituto di Astrofisica Spaziale, Rome, Rome, ITA 12345 Italy
Bibring, J (bibring@ias.fr) , Istituto di Astrofisica Spaziale, Rome, Rome, ITA 12345 Italy
Buratti, B J (a.@b.edu) , JPL, JPL, Pasadena, CA 91109 United States
Capaccioni, F (a.@b.edu) , Istituto di Astrofisica Spaziale, Rome, Rome, ITA 12345 Italy
Cerroni, P (a.@b.edu) , Istituto di Astrofisica Spaziale, Rome, Rome, ITA 12345 Italy
Clark, R N (a.@b.edu) , USGS, MS 964 Box 25046 Federal Center, Denver, CO 80225 United States
Coradini, A (a.@b.edu) , Istituto di Astrofisica Spaziale, Rome, Rome, ITA 12345 Italy
Cruikshank, D P (a.@b.edu) , NASA Ames, NASA, Mountain View, CA 94035 United States
Drossart, P (a.@b.edu) , Obs. de Paris-Meudon, Dept of Astronomy, Paris-Meudon, FRA 12345 France
Formisanno, V (Pierre.Drossart@obspm.fr) , Istituto di Astrofisica Spaziale, Rome, Rome, ITA 12345 Italy
Jaumann, R (a.@b.edu) , Institute for Planetary Exploration, DLR, Berlin, DEU 12345 Germany
Langevin, Y (a.@b.edu) , U de Paris Sud-Orsay, Dept of Ast., Paris, FRA 12345 France
Matson, D L (a.@b.edu) , JPL, JPL, Pasadena, CA 91109 United States
McCord, T B (a.@b.edu) , U Hawaii, Honolulu, Honolulu, HI 12345 United States
V. Mennella, V (a.@b.edu) , Osservatorio Astronomico di Capodimonte, Capitomonte, Capodimonte, ITA 12345 Italy
Nicholson, P D (a.@b.edu) , Cornell U, Dept of Astronomy, Ithaca, NY 14853 United States
Sicardy, B (a.@b.edu) , Obs. de Paris-Meudon, Dept of Astronomy, Paris-Meudon, FRA 12345 France
Sotin, C (a.@b.edu) , U Nantes, Dept of Astronomy, Nantes, FRA 12345 France

The Cassini spacecraft passed about 400,000 km of Titan on 2 July 2004. Titan's surface is seen in Visual and Infrared Mapping Spectrometer (VIMS) images at infrared wavelengths where methane, the principal atmospheric absorber, is transmitting. At 2.02 microns VIMS images show several circular features on Titan. These bear a striking similarity to circular features exhibiting topographic relief caused by impact events on a wide range of solar system objects. We undertook a photometric analysis of two circular regions using 2.02 micron images taken near the time of closest approach. We measured the reflectance along lines that passed through the sub-solar point on Titan's surface and traversed the center of each feature. The extracted reflectance profiles enabled us to search for vertical relief by comparing our photometric profiles with the profiles expected from a circular depression, a circular depression with a raised rim, and a circular depression with a raised rim and a central peak using a model based on the widely used bi-directional reflectance equations developed by Hapke (1993). We assumed: 1) the particulate surface scattered isotropically and had uniform single scattering albedo, 2) the haze was optically thin, did not extend to the surface, and was uniformly mixed laterally with the atmosphere. Despite our best effort to adjust the depression parameters to fit the data our data do not fit that expected for a craterlike depression. In one case the model fit does not agree with the data at large distances from the sub-solar point. In the other, the photometric profile expected from the central peak is in the opposite sense to that which we measured. In both cases the crater depths required to accommodate these best-fit models are extremely, if not unreasonably, large (~50 -100 km.) with diameters of 1000 and 2000 km.). We find it unusual to have two craters of such size on Titan because major cratering events are principally associated with the early bombardment period of solar system system-the first 1 billion years.Therefore, we suggest that these features are not caused by topographic relief and are not true craters. They are consistent with palimpsests-expressions of darker reflectance on a surface where the vertical relief has been lost to lithospheric plastic flow. If these features are palimpsests and are the remains of ancient impacts then their persistence on the surface suggests that widespread weathering processes, such as a planet-wide precipitation of aerosols, on Titan are severely limited. This result is consistent with Keck observations at shorter wavelengths by Bouchez.

Author(s) (2004), Title, Eos Trans. AGU, 85(47), Fall Meet. Suppl., Abstract #####-##.