There are hypotheses about a collision between Earth and an astronomical body the size of Mars, approximately 4.5 billion years ago, about 20 to 100 million years after the solar system coalesced.

I guess this changed the orbital path of earth around the Sun. Do we have any info what was the Earth's orbital path before the collision? (I would prefer some visual explanation.)

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    $\begingroup$ I'd close as too broad: any putative orbital change would depend on the mass and relative velocity (vector) of the two pre-collision objects. $\endgroup$ – Carl Witthoft Oct 10 '16 at 13:20
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    $\begingroup$ I haven't seen anyone make a claim as to knowing where the thing hit. Without that, velocity and elasticity as well, there's no way to come to a credible answer. $\endgroup$ – Wayfaring Stranger Oct 10 '16 at 14:58
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    $\begingroup$ There's some proposals on Theia wiki page and links - admittedly it's broad but I'm sure a partial answer is possible. $\endgroup$ – Andy Oct 10 '16 at 16:02
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    $\begingroup$ If Theia was in a trojan orbit (which is generally thought to be the case) then the effect would be small. Estimates would need to include lost debris that left the Earth's sphere of influence (hugely difficult to estimate), and perhaps energy lost into the Earth's angular momentum and maybe heat. Other than saying "not all that much because trojans share the same orbit", any calculations would be extremely rough. Now if Theia wasn't in a Trojan orbit, then the orbital change could be significantly higher. $\endgroup$ – userLTK Oct 10 '16 at 21:35
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    $\begingroup$ The question is not too broad. It's a legitime research question. The only problem is that very little is known about the answer, but a good answer can explain what we know, what we don't know and why we don't know. $\endgroup$ – Pere Oct 11 '16 at 16:25

The total angular momentum would always be conserved about the Sun (assuming it at rest), as there is no torque about the Sun. Apart from that, I think it is hardly possible to say anything about the orbits. Also, it may be true that the pre-collision orbital plane and the post-collision orbital planes changed due to the collision, as small transverse perturbations must also have resulted from such a collision. However, I would also like to see what other members suggest.


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