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ToSeek
2005-Jun-01, 05:55 PM
Icy Jupiter Moon Throws a Curve Ball at Formation Theories (http://www.spaceref.com/news/viewpr.html?pid=16985)


Scientists studying data from NASA's Galileo spacecraft have found that Jupiter's moon Amalthea is a pile of icy rubble less dense than water. Scientists expected moons closer to the planet to be rocky and not icy. The finding shakes up long-held theories of how moons form around giant planets.

Follow-up to an old topic (http://www.badastronomy.com/phpBB/viewtopic.php?t=18594&highlight=amalthea).

frogesque
2005-Jun-01, 07:52 PM
I'd been reading about this then saw your post (You do have to be quick round here :lol: )

On a sample size of one I wouldn't be too sure that current theories need to go out the window although that has to be a possibility. At the moment I would lever more toward a capture of a cold formed object (KBO?) If there was a significicant fraction of CO2 as well as water ice in its original composition then outgassing of CO2 in the warmer environment near Jupiter could lead to porosity and hence lower bulk density. It would be fascinating to see comparisons with other icy bodies like comets and maybe Deep Impact will shed some more light on this.

Jerry
2005-Jun-02, 02:20 PM
I'd been reading about this then saw your post (You do have to be quick round here :lol: )

On a sample size of one I wouldn't be too sure that current theories need to go out the window although that has to be a possibility. At the moment I would lever more toward a capture of a cold formed object (KBO?) If there was a significicant fraction of CO2 as well as water ice in its original composition then outgassing of CO2 in the warmer environment near Jupiter could lead to porosity and hence lower bulk density. It would be fascinating to see comparisons with other icy bodies like comets and maybe Deep Impact will shed some more light on this.

Why not lava rock? Lava rock - sometimes - has a density of less than one, it is sometimes red, and could have picked up some water alone the way. Perhaps spit out by IO

The other answer is that it is ~40% more dense than the flyby indicates, but that would be too ah, Jerry 8)

frogesque
2005-Jun-02, 08:18 PM
Interesting idea Jerry but I'm not so sure a light lava block (pumice?) could be ejected with sufficient velocity to escape a planet's gravity and also overcome the additional atmospheric drag caused by its size. Somehow I think heavy minerals and rocks would be favoured. So far as I'm aware no meteorites have been discovered on Earth with a low density. To have come from Io I think there would also have to be a very high sulphur signature

As for the +40% I'm just so not going there but I'm glad to see you haven't lost your sense of humour =D>