Sometimes (well, most of the time) astronomers are happy not to have paparazzi documenting our every move and blaring it on national news 15 minutes later. Last week was one of those times. Thankfully, I was not involved!
Several observatories in the U.S. (and around the world) spend every clear night looking for near-Earth asteroids. These are asteroids that have the potential to hit the Earth some day (maybe not for hundreds of millions of years, but someday). Roughly 5000 of these are known; most are pretty small (about 500 yards across or less -- large enough to wipe out a city, small enough that they wouldn't destroy the Earth). Most of these asteroids are discovered either just before or just after they come close to the Earth -- by close, we mean a few million miles.
On Thursday night, three different observatories discovered a near-Earth asteroid coming our general direction, and the initial estimates had the asteroid coming only 5000 miles away from Earth's surface today, which would have been the closest asteroid approach we've ever seen! There is also some error on that measurement, so we really didn't know exactly how close the asteroid would come. But it would be too close for comfort.
Bulletins raced out for more observations to better determine the asteroid's trajectory, and press releases were prepared. Then, before public announcements were made, a Russian scientist named Denis Denisenko noticed that the asteroid's path almost exactly matched that of a European space probe, Rosetta, that is swinging by Earth today on its way to visit a comet. In fact, this was no dangerous asteroid, but a human robotic spacecraft.
So, everyone could breathe a bit easier, even though many people probably feel they have a little egg on their face. The Minor Planet Center, the international organization responsible for monitoring all asteroids and comets, issued a statement calling for a better database of spacecraft orbits.
However, I see a silver lining in this fiasco. First, the system worked -- an unknown object that was going to come very close to the Earth was spotted before it arrived -- while a few day's warning would not be enough to save the Earth from a giant asteroid, it would be enough to protect people from a smaller asteroid through evacuations. (It would be possible to get a decent idea where an asteroid would impact.) Second, although the mistake was not picked up as quickly as we would have liked, it was discovered before the public was alarmed. And, last, we learned that there are some tweaks to the system that are necessary.