Theories of the origin of Luna? Earth getting glancing blows or near miss by "Mars-sized body"?

Question

I've seen description of theiries stating that a "Mars-sized body" made a near miss or hit Earth a glancing blow.

There are several areas on Mars with geological features that look like something BIG hit there.

Could it have been Mars ITSELF?

Answer 1

This has never been suggested in the original theory. The Mars-sized object is presumed to have been completely destroyed by the impact.

Perhaps the strongest indicator is the oxygen isotope ratios. For Earth and the Moon, the oxygen isotopes are 18 O / 16 O. (10 neutrons and 8 protons / 8 neutrons and 8 proton molecules)

Whereas on Mars, the ratios are 17 O / 16 / O. (9 neutrons and 8 protons / 8 neutrons and 8 protons)

This would suggest that the planetoid which struck Earth was formed in the same relative orbital path as the Earth. Mars' isotopic ratios would mean that Mars had formed in it's present orbit at 1 1/2 AU and never crossed Earth orbit.

A secondary indicator is that models show a collision with a Mars sized orb. Mars has only 1/10 the mass of Earth. In a collision between the two, unless it was a very obtuse oblique angle of collision, Mars would not have survived. Also, since we know that the Moon has an iron core, it makes the Moon's formation simply out of mantle material out of the two colliding orbs unlikely.

Answer 2

No, because there is nothing to explain how Mars then got back out into its current (farther) orbit.  Even if the impact changed its trajectory, it's orbit would still intersect Earth's as a result.  And it would probably take more than just a glancing blow for the moon to have formed out of it; not sure about that point, however.