Close Targets 
The Moon sails high across the sky tonight, illuminating the chilly night with its icy glow. It’s Earth’s only natural-born satellite. Like a busy foster parent, though, our planet could have had millions of temporary satellites over the eons -- asteroids that were captured by Earth’s gravity. And a team of scientists says that a future foster child could make a good target for NASA’s next major step in human exploration.
Thousands of asteroids follow paths that cross Earth’s orbit around the Sun.
A study led by Martin Elvis of the Harvard-Smithsonian Center for Astrophysics says that Earth can capture one of these asteroids if it passes close to a point in space where the gravity of Earth and the Sun are balanced. Spacecraft can actually orbit these points -- and some do.
At these points, the asteroid’s orbit can be deflected enough for Earth to capture it -- turning the asteroid into a small moon. Such objects can remain in orbit for anywhere from a few weeks to as long as eight years.
The study says that one of these long-termers might be a good target for NASA’s plans to send astronauts to study an asteroid. It would require a good search campaign to find and track these tiny bodies. But they’d be close to Earth, so it would take less time and fuel to reach them. And if it’s small enough, the astronauts could grab the whole thing instead of just samples -- turning a temporary visitor into a permanent resident of Earth.
Script by Damond Benningfield, Copyright 2010