[X] My Assistant

[alan]

Pluto and its large moon Charon may have been bowled over when they were struck by wayward space rocks in the past, a new study suggests. If so, NASA's New Horizons spacecraft may find evidence of these rolls when it arrives at the distant worlds in 2015.

Jay Melosh of the University of Arizona in Tucson, US, first suggested about 30 years ago that the basins gouged out by impacts would redistribute the mass of planetary bodies, causing them to roll over to re-stabilise themselves.

Assuming Pluto and Charon have basins as big as those on Saturn's moons Tethys and Rhea and Uranus's moon Titania, the researchers calculate that Pluto probably tipped over by 10° and Charon by 20°.

"One [prediction] is that there will be a network of tectonic fractures caused by the satellites rolling over," Nimmo says, explaining that their 'equatorial bulges' – a widening at their equators due to their rotations – would create stresses when their equators shifted position.

http://space.newscientist.com/article/dn12...pluto-over.html

Also check out the illustration of 'Pluto'. It looks a lot like this image of Ganymede.
http://photojournal.jpl.nasa.gov/catalog/PIA00352

[Rob Pinnegar]

I'm not impressed with this one.

Iapetus has got huge basins all over it. If *any* moon should have tipped due to impacts, it's Iapetus. However, the ancient bellyband (which most likely has something to do with the moon's original non-synchronous rotation) is still on the equator, suggesting that its rotational axis is stable.

In fairness, I guess one could make the argument that Iapetus' walnut-shaped profile would make it almost impossible to tip over, due to the enormous amount of mass distribution that would be necessary. But it's still just speculation -- and the fact that it's in New Scientist doesn't breed much confidence. Those guys seem willing to print anything.

[djellison]

If *any* moon should have tipped due to impacts, it's ....

Mimas, Phobos ?


Doug