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...

[ngunn]

with this new theory you aren't building on the prior theory you are completely rejecting it.

Accepted. (edit - something funny going on with the quote boxes here)

Quote fom J Rehling:
Without there being another large body at about 0.4 AU, there would be no way to draw that aphelion all the way in from 1.0 AU to 0.4 AU. (Which is a huge distance in gravity-well distance.)

It doesn't have to have been a single event. Scattering a lot of smaller objects and colliding with some of them might have done it. Similar processes have been invoked to account for giant planet migration. What would the region around 0.4 AU have looked like before there was a planet there? We have no idea.

More likely, there were once many planetary objects closer to the Sun and most got either thrown into the Sun or out into the far reaches of the solar system very early in the Solar System's history. The interactions would be far too complex to figure out. More objects would also mean that there would more likely be collisions. So you get the Earth-Moon system, the Venus Retrograde rotation, and the stripped down core of Mercury all from different collisions early in the solar system's history. Where did these object go? Some of them became part of the remaining planets. Others thrown out would be difficult to identify as such even if we were able to find them.

Actually I think the scenario quoted above is the most likely. The Mercury-from-Earth-collision idea probably suffers from trying to account for too much with a single event. There is no need to be parsimonious with our proposed collisions. Nevertheless it's interesting to think about. If it actually turned out to be true - well, the computer simulation people would just have to start again. I'm sure they'd come up with a model eventually. Myself, I'm going to be very sparing with the word 'impossible' until we have a lot more data. Mercury ahoy!!

[Rob Pinnegar]

Actually I think the scenario quoted above is the most likely. The Mercury-from-Earth-collision idea probably suffers from trying to account for too much with a single event.

Yeah. It's a neat idea and is very imaginative. But it won't work in practice.

Even if a grazing collision (between proto-Mercury and Earth) could somehow produce the Moon while sending Mercury plummeting inside Venus's orbit, there's still the problem of keeping it there (i.e. close to the Sun).

To do that, you need to postulate a second major impact on Mercury -- and an impact of that type happens to be one of the events this theory is attempting to replace.