Did an ancient impact bowl Pluto over? Options

[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

[tasp]

Re. Iapetus, perhaps equatorial ridge dates back only to 3.7 GYA, big 'moon rockin' impacts probably much older.

Joan for instance, if the 'tiger scratches' record to some degree a continuation of the flight path of it's impactor, studying crustal rigidity, and Joan's diameter, we might come up with a good estimate for the mass of that impactor. Looking at Iapetan radius in the bottom of Joan (not easy, I concede, due to subsequent impact damage) and comparing it to 'average' radius for the entire Iapetus (irregular though it is) might allow us to estimate increase in mass of Iapetus since that specific impact. If we can start working up some (relative, perhaps) dates for these features, maybe we wind up helping Alan when NH gets to Pluto. Additionally, more examples of this axial tilt idea might help pin it down (if it not spurious).

I am thinking Iapetus is taking on increased relevence to interpreting the NH Pluto/Charon/Nix/Hydra data in 2015. We are seeing several features unique to Iapetus, perhaps a subtle preview to some Plutonian strangeness.