We Earthlings owe a lot to the moon, and not just for its romantic appeal. The moon locks in Earth's tilt, which would otherwise be a bit wobbly. That in turn stabilizes Earth's climate, which is good for nurturing life. Without Earth's lunar companion, we might not be here.
The moon apparently formed from debris kicked up by a Mars-size object colliding with the young Earth. But the other terrestrial planets missed out. Venus doesn't have a moon. Neither does Mercury. Mars has two pebbles that barely qualify. So is Earth just an outlier, a freak cosmic arrangement of planet and moon that makes for a nice, life-enabling climate?
Not exactly. A team of researchers simulated the formation of hundreds of planets. And they found that nearly half of them experience giant impacts that produce a stabilizing moon. Almost 10 percent wind up with a massive moon comparable to our own. The research appears in the journal Icarus. [Sebastian Elser et al., "How Common Are Earth–Moon Planetary Systems?"]
That means that if Earth-like planets exist in large numbers throughout the galaxy, at least some of them ought to enjoy the benefits of a moon. Romantic and otherwise.
[The above text is an exact transcript of this podcast.]