The Mayans have plans for the Earth this Friday—destroying it to
be specific. Let’s pretend, however, that that forecast doesn’t
hold up to close scrutiny and that against all odds, we wake up
in one piece on Saturday morning. That will free us to turn our
attention to another way the world could end—rogue asteroids or
comets—and those doomsday scenarios actually have the attention
of scientists. The incoming ordnance the researchers most fear
are those known straightforwardly as Near Earth Objects (NEOs).
The dinosaurs could tell you a thing or two about the danger of
such free-flying rocks. Oh wait, they can’t. Not any object we
can see earns the Near Earth label. It has to be on track to
enter the air space of our solar system, passing within 1.3
astronomical units (AU)—or 121 million miles—of the sun. (A
single AU is 93 million miles—or the Earth-sun distance.) Going
by that standard, NASA estimates that there are thousands of
NEOs out there, though the ones that worry them the most are the
ones that meas