Speculations and hypotheses about Theia

[Gliese123]

As the topic says: What's your speculations about Theia? Was it really the reason that the Moon appeared and what would have happened if Theia became a part of Earth's orbit instead of been smashed into Earth? http://en.wikipedia.org/wiki/Theia_(planet)#Theia

 

[qraal]

As the topic says: What's your speculations about Theia? Was it really the reason that the Moon appeared and what would have happened if Theia became a part of Earth's orbit instead of been smashed into Earth? http://en.wikipedia.org/wiki/Theia_(planet)#Theia

If Theia existed then it most probably formed in one of the Earth-Sun Trojan points, as the impact had nearly zero hyperbolic excess. Personally I think there is an alternative to the "Big Smash" origin for the Moon. Robert Malcuit, of Denison University, demonstrated how the Moon could have been captured from a solar orbit about the same time as the Big Smash received "support" from simulations on super-computers in the late 1980s. So two alternatives exist, at least.

 

[Nik_2213]

Latest idea to account for the much thicker crust on Lunar farside, IIRC, is that either part of the impact splash 'escaped' back to a Trojan / 'halo' orbit, or formed a mini-Moon in a wider Earth orbit.

In former case, similar orbital perturbations to those by Venus and Jupiter that dumped Theia onto the proto-Earth swung the mini-Moon to meet our Moon. In latter case, as our young Moon's initial close orbit rapidly retreated due tidal dissipation, the mini-Moon became road-kill...

Uh, one problem with such scenarios is conserving momentum. IIRC, the 'Big Splash' didn't seem likely until extensive computer modelling showed how much of the impactor could become an orbiting arc of debris which could then accrete as our Moon. Also, IIRC, Theia's impact speed and angle plus the direction and speed of proto-Earth's rotation had to lie in a fairly narrow range for our Moon to emerge...

I haven't seen more than casual speculation on the possibility that Mercury & Venus are the result of a Theia-like impact that turned out badly, such that Mercury left its crust on Venus and almost stopped her rotation...

( Yes, I know that scenario's momentum conservation post-impact currently presents a problem. As the Messenger probe found that, at ~1500x1300 km, the Caloris basin is both more elliptical and larger than suspected, there's a possibility of a third-body event ... ;- )