Newest Ideas about Planetary Collisions

[dougettinger]

New ideas about planetary collisions have surfaced since I last had discussions on the forum about this topic.

I have recently noticed on a Science channel on TV (I do not watch TV networks too often) that certain kinds of planetary collisions are being animated. Some of the narrators are respected scientists and possibly some of the animations are produced by NASA affiliates.

These collisions are between two sizable bodies, not just an asteroid or cometary size hitting Earth. These major impacts do not destroy these bodies. The larger body absorbs the smaller body (comparable to Earth absorbing Mars) producing debris that is only a very small fraction of both bodies. The two bodies have effectively a coefficient of restitution of zero (no elastic rebound).

Wikipedia is now categorizing stages of accretion of the inner planets as "runnaway accretion", "oligarchic accretion", and "merger stage accretion". The last two stages definitely will require the subject collisions to leave one remaining planet in each orbit. The "Giant Impact Hypothesis" that formed the Moon supposely was only a glancing impact. There was a strong opinion only a few years ago that these major-type collisions would destroy both bodies.

Has a major shift in thinking about this type of collision occurred in the scientific world?

Always watching for paradigm shifts,

[dougettinger]

I guess collisions have already become a boring subject. Is there any estimation of the minimum ratio of two large masses colliding with each other with a moderate planetary velocity differential and not self-destructing ?

Trying to deploy the forum,

Doug

[bystander]

http://asterisk.apod.com/viewtopic.php?f=31&t=29794
http://asterisk.apod.com/viewtopic.php?f=31&t=29795

[dougettinger]

Dear Bystander,
Thank you for providing these excellent papers on the subject. I believe you have given me my answer. The paradigm shift is due to attempts for arriving at better collision scenarios to create the Earth-Moon system and address the isotopic anomalies discovered during our Moon exploration. More experimental computer simulations are revealing what can happen in collisions of two large bodies. Of course, the accretion theory of the inner solar system bodies requires collisions that will combine bodies rather than splatter them apart.

Doug