Cat Scratches and Tiger Marks

Cat Scratches

Strange features on Titan named cat scratches which were seen by radar observations from the Cassini spacecraft. CREDIT: NASA/JPL

The image above was taken by the Cassini spacecraft and shows a region near the equator on the surface of Titan. It is actually a radar measurement because you can't see through Titan's thick haze with an optical camera. The particular part that I want you to look at are the strange horizontal marks to the left and far right. These have been nick-named "cat scratches" as they look as though they have been made by a rather large feline. They are particularly interesting because if you look at all of them - over the whole moon - they all seem to be aligned in an east-west direction to within about five degrees. What causes them is a bit of a mystery, if you discount moon sized cats. However, it was suggested yesterday that there may be similar features in Antarctica. We were shown a picture of similar(ish) marks taken by radar over Antarctica. These features couldn't be seen by eye on the ground as they weren't physical ridges. They were just different sized grains of snow that had probably been sorted by the wind into a wave pattern. Perhaps the same has happened on Titan?

Enceladus and the UK

A comparison of the UK and Saturn's moon Enceladus CREDIT: Stuart (based on an image presented at DPS2005 in Cambridge)

Now on to Enceladus which has proved to be incredibly interesting in its own right and is giving Titan a run for its money in terms of excitement here. The image to the right is my recreation of the one we saw during one of the talks. It gives a rough size comparison of Enceladus with something a bit more familiar.

Back on 17th February, Cassini made a fly-by of Enceladus getting as close as 1200 km. Measurements of Saturn's magnetic field showed some deviations from what would be expected and the suggestion that Enceladus had an atmosphere was put forward as a possible explanation. To find out more, a second fly-by was organised which went closer. This showed even more strange things happening to the magnetic field, so a third, super-close, fly-by was scheduled.

On 14th July, Cassini got as close as 173 km to the surface - closer than the ISS is to the surface of the Earth. Putting the data from all three fly-bys together suggests that strange things are happening at the south pole of Enceladus. The current idea that is popular here (and it is backed up by measurements on several instruments) is that there is some type of out-gassing near the south pole. What exactly would cause this, nobody is quite sure. However, like Titan, Enceladus also has some strange marks. In this case, they have been called Tiger Marks and are found exclusively near the south pole of the moon. These stripes - dare I call them ridges? - consist, chemically, of ice and organics. Temperature measurements show that they are warmer than the surrounding area by a significant amount. Perhaps there is some kind of ice volcano (cryovolcanism) at work?

Stuart is currently at the Division for Planetary Sciences 2005 Meeting in Cambridge, UK. The meeting is run by the AAS in cooperation with the RAS.

Posted in astro blog by Stuart on Tuesday 06th Sep 2005 (18:08 UTC) | Permalink
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