I've been browsing a NASA report given to Congress this month titled Near Earth Object Survey and Deflection Analysis of Alternatives.
The report lists the pros and cons of various ways stopping gigantic rocks from falling from the sky and either ending life "as we know it" (how *do* we know it, anyway, I've always wondered?), or if not that, causing so much damage as to render moot this (and every other) question that might come to mind.
I've had a bit of difficulty, conceptually, with the term NEAR EARTH OBJECT, since it suggests something that's always lurking in our Earthly neighborhood, maybe hiding behind the moon, or tracking our planet like a malevolent highwayman, hiding in the Earth's penumbra. Surely these NEOs just swing by occasionally in the elliptical fashion, and are only truly deserving the NEO name when they've got a chance to hit the bulleye? That's got to be the case, right?
Or maybe some of these giant rocks are even in orbit around the Earth? Or whipping around the moon in an unstable, numerically threatening orbit?
This report seems to say no, the rocks of interest are on orbits that correspond roughly to what I'd imagined. This diagram helped clear up the situation for me:
So there you have it, four possible horsemen of the apocalypse: Apollo, Aten, Amor, and Apohele.
I'm not surprised to find these devils all have names that start with "A".