27 May 2008

T44 is the ninth in a series of outbound encounters and the last Titan encounter in the nominal four-year mission, or Cassini's Prime Mission. The extended mission, named the "Saturn Equinox Mission," will follow-up on the nominal mission this summer and will last two years. It includes 26 Titan flybys, as well as 7 Enceladus encounters, and one flyby each of the icy moons Dione, Rhea and Helene.

The T44 encounter is set up with two manoeuvres: an apoapsis manoeuvre on 21 May, and a Titan approach manoeuvre on 24 May. It occurs just over two days after Saturn closest approach.

Science Highlights

• Cassini Radar (RADAR)
  T44 altimetry will be close to Hotei, over an area that was SAR imaged during the previous flyby, T43. The SAR swath sweeps northwest across Xanadu, over the Shangri-La dunefields and onto Dilmun. The SAR will image the southern edge of Xanadu, which shows a sharp boundary in microwave emissivity that is not presently understood. The SAR data is hoped to yield information on Xanadu's large-scale topography, as well as the influence of Xanadu on regional wind patterns as revealed in the dunes, and a partial overlap with T13 SAR may give stereo information and refine estimates of Titan's rotation state.
• Ion and Neutral Mass Spectrometer (INMS)
  INMS uses the RADAR orientation, and because of the higher altitude of this flyby the spacecraft is above most of Titan's ionosphere and INMS will obtain exospheric observations. The team will use these observations to identify what chemical compounds are escaping from Titan's atmosphere, looking at both altitude and the difference between the northern and southern hemispheres.
• Composite Infrared Spectrometer (CIRS)
  CIRS continues to extend spatial and temporal coverage of Titan, from low-spectral resolution disk maps to high spectral resolution nadir and limb integrations. Getting good time resolution is very important because we are looking for seasonal changes in the stratosphere, especially the expected break-up of the northern polar vortex in northern spring. In a rare occurrence, during the T44 targeted Titan flyby, CIRS will be observing the rings of Saturn. Usually, the Titan observations are considered more compelling during the flybys since the geometries and opportunities are so spectacular. These ring observations are therefore quite unique. CIRS will determine the mean thermal gradient across Saturn's many-particle-thick rings by executing radial scans of Saturn's main rings (A, B & C) over multiple illumination geometries (including phase, spacecraft inclination, and solar elevation) on the lit and unlit sides of the rings.
• Visible and Infrared Mapping Spectrometer (VIMS)
  VIMS observations concentrate on determining time scales for cloud formation and dissipation.
• Imaging Science Subsystem (ISS)
  The T44 flyby geometry shows a half-illuminated Titan as Cassini approaches and recedes. On approach ISS will carry out night-side imaging for photometry and will search for lightning and aurora. ISS will also acquire a regional-scale map of Hotei Arcus, its highest-resolution observation of this region to date. Outbound, ISS will see portions of Belet and Adiri and territory to the north, capturing global and full-disk mosaics. As the geometries of the T41 through T44 flybys are very similar, ISS has opportunities to detect clouds in this region every few weeks.
• Radio and Plasma Wave Science (RWPS)
  As Titan is out "in front" of Saturn, the T41 through T44 flybys put the spacecraft in an ideal location to have another opportunity to see Titan outside of Saturn's magnetosphere, in shocked solar wind ahead of the magnetosheath as happened on T32. We are interested in duplicating the flyby geometry to look for shorter time-scale phenomena in Titan's plasma environment, so this series of four flybys, especially T41 through T43, will offer that opportunity.

Table of events

19 April 2008

24 May 2008

25 May 2008

26 May 2008

27 May 2008

28 May 2008

29 May 2008

Titan Ground Trace

Image courtesy NASA/JPL/Space Science Institute

The above image shows the ground trace of the Titan-44 flyby on a mosaic of Titan's surface, for a period of 32 hours around closest approach (going from ~45° to ~264° longitude). The colour of the trace indicates Cassini's altitude above the surface. Blue: > 100 000 km, green: < 100 000 km, light blue: < 50 000, yellow: < 10 000 km, orange: < 5000 km, red: < 2000 km. The point of closest approach is marked T44 (Cassini at 1400 km altitude).

Observation Results

Cassini Instrument: Cassini Radar (RADAR)

Date: 8 August 2008 Credit: NASA/JPL Image Notes: Radar image of 450-km wide area at the edge of Xanadu (bright region at the top), at 15° S, 121° W, revealing several channels up to 5km wide.