Arecibo Pins Down an Asteroid Orbit

That's a bit of an overdramatic title, but it's true that the most efficient way for us to reduce the risk we face from asteroids that have a very small chance of hitting Earth in the future is to determine their orbits more precisely. As surveys get better and better at picking up smaller and smaller objects, we are going to be hearing about more and more bodies that have slight chances -- one in a million chances -- of hitting Earth. But these small things are very hard to follow up on because they are so small, so their orbital paths can remain uncertain. It's bad for future planning not to really know whether we're going to be hit by something or not. So it's wonderful to have radio telescopes like Arecibo that can bounce signals off of asteroids to determine their position (and, incidentally, their size) very precisely.

That's what Arecibo did last week, bouncing a signal off of near-Earth asteroid 2005 YU55. As its name suggests, 2005 YU55 was discovered in 2005; actually it was discovered right at the end of 2005 (that's what the "Y" tells you), presumably when it was relatively close to Earth.…

Also see Space.com and the Bad Astronomy Blog.