How a Mars-Sized Object May Have Built the Moon
The Moon may be a leftover from a collision. In NASA's account of the giant-impact hypothesis, a Mars-sized object called Theia smashed into the infant Earth, vaporizing massive amounts of rock and blasting it into space; some of that material then coalesced into the Moon. NASA frames this as something scientists theorize, not something anyone watched happen — which is the right level of confidence for an event that left no witnesses, only debris that is still overhead. That debris is now a destination: NASA says its Artemis program is returning humans to the Moon as part of preparing for Mars.
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The detail worth keeping is the sourcing: NASA presents the giant impact as a theory about the early solar system. A Mars-sized impactor is a hypothesis doing explanatory work, not a logged event.
Which is part of the appeal. The account is a piece of recycling — rock vaporized off a young planet, then reassembled into the thing we now plan to visit.