Wednesday, July 06, 2005

Raw Images of the Day


Anonymous Anonymous said...

These Saturnian icy moons have a lot of similarity with Tempel 1 in surface characteristics and composition, could they be caputured comet nuclei?


7/07/2005 01:05:00 AM  
Anonymous Phil Stooke said...

The basic idea is good, but there are two major differences: the moons are MUCH bigger, and they are in orbit around Saturn. These factors allow different things to happen: they can differentiate into rocky interiors and icy outer parts, whereas the comet presumably can't do that. They can hold more radioactive material to heat their cores, and being bigger and close to a big planet they can be heated by tidal effects. The heating then drives other types of geological activity: tectonics (fracturing the crust), maybe volcanic-type eruptions (some smooth plains units here and there). Also the moons are in an environment where lots of impacts have occurred. The comet has a different history, including evaporation (sublimation) of surface material during closer passes by the sun which the moons never experience.

So lots of differences... but I'd probably link them by saying the comet is an example of the building blocks the moons were made from originally.


7/07/2005 09:35:00 AM  
Anonymous Phil Stooke said...

OK, it's basin identification time on Rhea. I've been looking at the Tirawa region, in the image Jason links to here plus other views of it. There are two big basins, each about 300 to 350 km across - Tirawa on the upper right (northeast) and a similar basin to the southwest. Tirawa was found and named in Voyager images back in 1980. The second was discovered by yours truly in specially processed Voyager low-resolution images and described at LPSC in 2003. BUT... I now think there is a third similar-sized basin in these images. Its northern rim is one basin diameter south of the south rim of the un-named basin just described. It is only fuzzily seen in the image Jason links to, but better in other images. It's a bit more degraded so there might be more dispute about its existence, but I think it's real. You heard it here first... It seems basins are more common on these moons than was suspected before Cassini


7/09/2005 08:26:00 AM  
Blogger Jason said...

hmm, well, we may get a better view of it over the next two orbits.

7/10/2005 10:16:00 AM  

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