Needless asteroid paranoia

A bunch of people (Slashdot, Instapundit, Jane Galt) have been worrying about an asteroid with a relatively high probability of Earth impact. But what does NASA have to say about its own probability calculations?

The probability computation is complex and depends on a number of assumptions that are difficult to verify. For these reasons the stated probability can easily be inaccurate by a factor of a few, and occasionally by a factor of ten or more.

In other words, don't take these calculations too seriously. NASA also makes the point that larger errors are present in the probability calcuations of newly discovered objects. This asteroid has only been observed for 187 days, but its impact is projected in 25 years.

The uncertainty in the orbital elements also depends on the number of observations and the time span over which they are made. The more observations we have, and the longer the time span, the less the uncertainties will be, and the more precise the orbit will become. Thus, for a newly discovered object, the uncertainties tend to be large initially. As more observations are obtained on the object's position, the uncertainties are reduced, and any potential impacts are then eventually eliminated for the vast majority of the cases.