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Emily Lakdawalla • Jan 11, 2008

Titan's south pole looks pretty dry

One of the major results from the Cassini mission last year was the production of a mosaic of images from its RADAR instrument covering Titan's north pole. Titan's north pole has lakes upon lakes, some big, some small, but everywhere you look, there they are.

Cassini RADAR view of Titan's north pole, October 2007
Cassini RADAR view of Titan's north pole, October 2007 This mosaic is composed of all synthetic-aperture-radar maps of Titan's polar regions acquired by Cassini to date. It has been cropped and reduced in size by 50% from an even larger mosaic available on NASA's Planetary Photojournal. Approximately 60 percent of Titan's northern polar region (poleward of 60 degrees north latitude) has been mapped as of October 2007, and of this area, about 14% appears to be covered with hydrocarbon lakes. The radar images are grayscale; they have been colored here with a color map that applies blue colors to the materials that are darkest to the RADAR instrument, and yellow colors to the materials that are brightest. This color scheme highlights the apparent lakes, but also shows that many lake-like features are not as dark as other lakes, and that darker channels appear to run down the interiors of less dark lakes.

The image is a polar projection, with zero longitude (the sub-Saturnian hemisphere) toward the bottom. The leading hemisphere (centered at 90 degrees W) is to the left, and the trailing hemisphere (centered at 270 degrees W) is to the right. The largest lakes are clustered in an area on Titan's trailing hemisphere.Image: NASA / JPL-Caltech

By contrast, there do not appear to be nearly as many lakes in the south. Here's one image showing a south polar swath released in October. There are lots of what appear to be dry lake beds, but only one or two spots that may currently be fluid-filled.

Lakes at Titan's south pole
Lakes at Titan's south pole Cassini's RADAR instrument acquired its first swath across the southern polar region on 2 October 2007, reaching to within 18 degrees of the south pole. Within the swath are small, irregularly shaped, radar-dark blobs much like the features that are now being interpreted as lakes in the northern regions, as well as many other features that share similarities with ones seen in the northern polar region. The similarity between the poles suggests that the surface features in the polar region are driven by Titan's climate.Image: NASA / JPL-Caltech

On December 20, Cassini flew straight across the south pole and likewise spotted only one or two lakes.

Titan's south pole
Titan's south pole Titan's south pole is considerably drier than the north pole, as this RADAR image from Cassini's 20 December 2007 (T39) flyby proves. The swath is about 760 kilometers long by about 150 kilometers wide, and contains rugged mountains interspersed with flat-floored basins. Only two apparent lakes are contained in the image, a contrast to the dozens of lakes visible in north polar images. The difference probably has to do with the current season on Titan; it was the end of summer at the south pole and end of winter at the north pole during most of Cassini's primary mission to the Saturn system.Image: NASA / JPL-Caltech

The fact that you can see dry lakebeds and lots of sinuous river-like features both north and south suggests that the landscapes we see in both places are primarily carved by climatic rather than tectonic events; the fact that one pole is wet while the other is dry suggests that the climate changes with the season, as it's been summer lately in the south and winter in the north. Saturn and Titan will see their equinox in a year and a half, August 2009. Cassini's extended mission will last beyond that, so hopefully we'll get a chance to see the effect of changing seasons on Titan's polar weather.

Speaking of the extended mission, I have thoroughly revised and updated my detailed timeline of Cassini's mission to Saturn, including a complete list of the events to take place during the extended mission. Check it out and see what's in store!

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