Mercury - a left-over of the crash that created the Moon?, Highly speculative but maybe worth it Options

[karolp]

Having agreed upon the Moon being created by a grazing collision with a Mars-sized object, could we give any thoughts to what happened to the impactor afterwards? Since it was a grazing collision, it might have been melted but not destroyed, only with some material ripped from it (and from the Earth) which ended up in Earth orbit to coalsce into what we know as the Moon today. But what happened to the impactor after it passed the Earth? Could it still hang around somewhere in the Solar System? I suppose it would bear some significant markings after the event, for instance have its outer layers stripped. But wait a second... Mercury DOES have its outer layers stripped off, with an unusually high mean density resulting from a core which could be considered oversized for such a small planetary body. In the wake of MESSENGER beginning to reveal Mercury's secrets in January, could anyone bother to give any thoughts to this idea? I am not sure whether it had been put forth previously or not, I am just curious if it could make any sense to have the impactor impact the Earth in a grazing manner and then end up parked in an elliptical orbit close to the Sun, with its outer layers stripped and an "oversized" original core left inside...

[vk3ukf]

Hi, I never realised that Mercury has such a strange orbit around the Sun, I just downloaded a gravity sim and speed it up, and I thought there was something wrong with it. Mercury apears to have a highly eliptical orbit that rotates as well.
Or is my grav sim a bit bonkers.
If Mercury had formed where it is now, would the orbit not be a lot more circular?
I think back to the theories that were developed when they were looking for planets and a chap came up with the planetary orbit resonance theory, that predicted a planet between Mars and Jupiter, but they only found asteroids. His numbers fit fairly well.
It was called the Titius-Bode law.
http://metaresearch.org/solar%20system/eph/eph2000.asp

[JRehling]

Yes, Mercury has a pretty notably eccentric orbit. It's so deep in the Sun's gravity well that the tugs that other planets might exert are comparatively quite minimal. But an eccentric orbit is no less stable than a circular one. Presumably, random accretion events tend on balance to circularize orbits, but once accretion stops, the circularization stops, too, and Mercury's orbit is actually a lot less eccentric than most extra-solar planets, not counting those that are so close that tides have circularized them.

Since Mercury's rotation has been synchronized with its revolution (3:2 ratio of periods), there was probably some tidal circularization of its orbit as well, but it's much farther out than your typical hot Jupiter.

The "rotation" ("precession" is the preferred term) of Mercury's aphelion is actually due to relativistic effects, not the pull of other planets, and was one of the early points of validation for General Relativity.