Jason PerryMar 12, 2007

LPSC: Wow, Titan can be a Really Flat Place, and other Titan Talks

I was sent this update on the Titan sessions at LPSC by Jason Perry, a member of the Cassini Imaging Team and an undergraduate student at the University of Arizona. He used to write a blog called Titan Today, and is a big fan of Io. Thanks Jason!! --ESL

This week's Lunar and Planetary Sciences Conference (LPSC) in Houston, Texas, is the fourth time I have been to this conference. The previous three trips to LPSC were to present a poster, either about the Gish Bar Patera volcano on Io or Cassini ISS images of Titan. This year, however, I presented a talk, during Monday's Titan session. The session was filled with the latest results from Cassini's many instruments, including RADAR, ISS, and the Visible and Infrared Mapping Spectrometer (VIMS).

The first two talks in this afternoon's session covered results from the Imaging Science Subsystem camera onboard Cassini. The first talk, by Elizabeth Turtle, gave a general overview of recent results from ISS. Perhaps the biggest news is a large lake, a sea even, discovered in Titan's north polar region late last month.

Giant lake near Titan's north pole
Giant lake near Titan's north pole This view of the north pole of Titan taken on February 25, 2007 contains a large, dark feature with arcuate edges, very likely a giant lake like those seen by the RADAR instrument. The feature is approximately 1,100 kilometers (680 miles) long and has a surface area slightly smaller than that of Earth's largest lake, the Caspian Sea.Image: NASA / JPL-Caltech / SSI

The northern portion of this sea, extending over 1,100 kilometers across with an area nearly equal to that of Earth's Caspian Sea, was also seen by RADAR during the late February T25 encounter, a couple of days prior to the ISS observations. [Here's that lake. --ESL] However, to date, ISS has yet to see a specular reflection (similar to what you see when seeing lakes late in the afternoon from an airplane) that would definitively indicate the presence of liquids. The identification of this dark feature as a lake, therefore, is based on the morphology of the feature and the appearance of the sea in RADAR.

I gave the second talk of the session, covering ISS observations from a flyby in late October 2006 (T20). This high-resolution observation covered a portion of Titan's trailing hemisphere. This region contains the bright streaks the VIMS team interprets as mountain chains based on data taken during the same encounter. The region also contains several features that share many of the morphologic characteristics seen in lake-like features seen in the polar regions by ISS and RADAR. These features are seen in an area where clouds have repeatedly been observed by ground-based observations and VIMS. Again, we haven't observed specular reflections at these sites, so we can't say for sure if these features are lakes, but they are certainly worth a closer look by RADAR.

A mountain range on Titan
A mountain range on Titan The VIMS instrument on Cassini captured this view of a mountain range on Titan just south of the equator on October 25, 2006. The mountain range runs from northwest to southeast across the image and is made visible by the subtle effects of topographic shading on this cloudy world. The color image is composed of infrared views captured through three methane "windows" at 1.3 microns (blue), 2 microns (green), and 5 microns (red).Image: NASA / JPL-Caltech / U. Arizona

The next few talks were given by members of the RADAR science team. Besides the usual talks about lakes and dunes (don't worry, I'll talk about those in a minute), perhaps the most interesting talk was one given by Ralph Lorenz on the RADAR altimeter. Precious little data has come out of the RADAR team regarding the altimetry experiment, save some early plots from our first Titan encounter. Much of the older data was subject to significant errors due to uncertainties in the position of Titan early on in the mission, but these uncertainties have been significantly reduced, and better-quality results have been obtained. Lorenz presented a number of plots of altimetry data, showing the utter flatness of the dune fields, though individual pulses do sense both the top of the dunes and bottom of the dunes, and these two altitudes agree with earlier topographic measurements from the RADAR SAR data. Lorenz also presented altimetry data over a portion of the ISS T20 mosaic, which might provide a chance at co-analysis. This greater confidence in the usefulness of the altimetry mode on RADAR has led to the development of a several-thousand-kilometer-long altimetry swath to be acquired during an encounter in May 2007. This swath will also be used to test the reliability of "altimetry from SAR", a technique of using the RADAR SAR's central beam as an altimeter, potentially increasing the amount of altimetry coverage on Titan.

Jani Radebaugh and Karl Mitchell of the RADAR team also presented talks, on the dunes and lakes seen by RADAR, respectively. Each new RADAR swath in recent months has provided additional observations of the lakes observed in the north polar region and the dunes observed within the equatorial dark regions. These results support many of the original conclusions, that the dunes represent an pole-to-equator transport of dark Titan sand (made possibly of benzene, so I suggest one not eat Titan sand...), with the occasional diversion around a local topographic high, and that the dark north polar features really are lakes filled with liquid, though some partly drained lake basins have also been observed. One interesting result from Karl Mitchell's talk suggests that the amount of liquid covering Titan's surface fits nicely with a prediction made by a research group led by Giuseppe Mitri, finally published last month in the journal Icarus. The overall climate pattern suggested by RADAR, of relatively humid polar regions supporting lakes on the surface and relatively arid equatorial regions leading to great sand dune seas, is supported by Mitri's model.

Two other talks rounding out the afternoon session covered VIMS results at Titan. The first talk, given by VIMS Principal Investigator Bob Brown, covered evidence for a large impact basin in the eastern part of the dark region known as Aztlan. The eastern portion of this dark region is bounded by a semi-circular bright region, interpreted by Brown and his group as the eastern portion of this large impact basin. Based on VIMS' spectral data, the interior of the possible impact basin is filled with the longitudinal dunes that are ubiquitous within Titan's equatorial dark regions. Jason Barnes gave another VIMS' Titan talk, this time on co-analysis of VIMS and RADAR data of dark spots and channels in eastern Xanadu. His analysis shows that some of the dark spots seen by VIMS and ISS are in fact, when seen by RADAR, small mountain ranges. Further analysis suggests that water ice-enriched material eroded from these mountains is channeled away and deposited along the margins of Titan's bright terrain.

Luckily, my laptop's battery power just barely made to the end of the last talk of the Titan session, allowing me to type notes for all the talks at the session. The next four days will be a little strange for me, since I usually have to wait longer to present my work, this year I am finished by the end of day on Monday. There will no doubt be many interesting presentations to attend before Friday.

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