Saturday, July 7, 2007

You`re as cold as ice but............less dense.

Yes,you want to click that picture
Hyperion is a moon of Saturn, and it’s freaky. It’s one of the largest irregular moons in the solar system at 300 km across, and the surface is simply weird. I speculated about it before, and it looks like some of my thoughts have panned out. When the Cassini spacecraft passed by Hyperion, the gravity from the tiny moon deflected the probe just a hair, and from that scientists have been able to find that the density of Hyperion is an astonishing 0.5 times that of water! For comparison, rock is about 2 - 3 times as dense as water, and even ice is 0.9 times water’s density. I think this makes Hyperion the lowest density object yet found in the solar system. So why is it such a puffball? Probably it’s suffered multiple low speed impacts with other bodies. This ruptured the moon, creating cracks and fissures all through it. If it got whacked by something of just the right size and speed, it could have actually broken apart and recoalesced; forming what astronomers call a "rubble pile". It would have so many holes in it that this would account for the extremely low density. Note– I’m still speculating, but it’s hard to imagine what else could have caused this moon to be so lightweight. It’s covered in craters, too. The surface is so porous that when an impact occurs, it actually compresses the surface rather than blowing out material. The moon can absorb the impact better without disturbing the neighboring terrain (and any material ejected tends to escape the feeble gravity of the moon, so that it won’t blanket nearby craters either). On normal moons, an impact is likely to erase several craters as the material is disturbed, but on Hyperion the impactor goes crunch, like punching a piece of Styrofoam. I wonder… when you walk on certain kinds of snow, you can feel it crunch as it compresses underfoot. Would an astronaut on Hyperion feel the same thing?


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