I remember reading a long time ago that the planet once had two moons- however, the second moon fell to the earth and was obliterated. So, I wonder, if the moon we've got now is a Forerunner creation, made to protect the planet? It would fit well, considering how AR is based on the phases of it- He knows where it's going to be, they made it like that.

I think the leading theory about how the moon came into being at the moment is that while the earth was still just a mass of molten material formed from the leftovers of the birth of a star, a very large mass of iron impacted the earth and started a chain reaction that gave earth its iron core and flung other materials into orbit creating the moon. This theory was generated by the fact that tests on lunar soil show that it has almost no iron content at all but still has most other substances found in our soil except the biomass left behind by dead organisms, ex. dead bodies, bodily waste, dead plant matter.

Unless its orbit changed suddenly and drastically, which isn't terribly likely, a moon would have been torn apart by tidal forces before it impacted the Earth, and we'd see evidence of it in the form of debris or rings around Earth's Roche limit. I've never heard of this second-moon theory, but I have heard of the one ProfessorHojo05 mentioned, as well as stranger and much less credible ones about Mars and Earth being formed from the same proto-planet, or Venus formerly being the core of a comet.

No. The planet used to have NO moons. That is until a giant asteroid came crashing(the scar is speculated to be pacific ocean) and the rock blasted out became the moon. NOT 2 moons. Wikipedia says NO.

That is all.

Actually it was an enormous rice ball, composed entirely of space-rice.

All praise wikipedia!

You do know that Wikipedia is user-editted and user-controlled, right? You can go post that the moon was made from Space Rice and if no one notices it to change it, it will stay, and people like you will take it for fact.

Lesson: just cuz it's on Wikipedia, doesn't make it fact.

This is from a lecture I attended at the Harvard-Smithsonian Center for Astrophysics (unfortunately I can't find an exact transcript, but I have notes)

The Earth was originally much smaller, but at some point early on, a massive planetoid, close to the size of Mars, impacted. Both were destroyed, but eventually most of the matter was pulled together and formed the present-day Earth. The remainder of the matter formed the moon.

The Forerunner seem to ejoy inatallations with an atmosphere, not one acessable only through vacum (with, of course, the notable exception of one particular multiplayer map from the first Halo). Besides, with all the things that they have on earth (refer to covenant excavations mentioned at the beginning of Ghosts of Onyx), what do you need something up there for?

Wait, which map is a forerunner installation in a vacuum?

Derelict, also known as "Deep Spcae Anomaly #0198"