Yesterday, Roger Ebert tweeted:
Bad luck. The asteroid that came so close to Earth is coming baaaaak. dld.bz/chPtq
Well, of course. It’s a known near-Earth object. They do that by definition. But the linked article by Andrew Malcolm at Investor’s Business Daily was a little more alarming than that, at least until I realized he was making stuff up:
Now, about that other bad news. According to the same computer calculations, in 2080 the orbit of 2012 AD 14, if unaltered in these next 67 years by some super-natural force like Bruce Willis, will slam into Earth at almost 18,000 miles an hour.
That explosive encounter, NASA says, will release about 2.5 megatons of energy into the atmosphere, causing “regional devastation.”
First of all, there’s no asteroid called “2012 AD 14.” The proper designation of the asteroid that just flew past the Earth is “2012 DA14” indicating that it was the 351st object logged with the Minor Planet Center in the second half of February 2012. (Whole ugly numbering system explained here.)
Second, the day after it passed the Earth — and two days before the publication date on Andrew Malcolm’s article — it was removed from the Sentry Risks Table. That’s the up-to-date listing of all potential collisions by known asteroids for the next 100 years.
Newly discovered asteroids get added to this list if the margin of error for their projected orbital track could possibly allow them to hit the Earth on one or more dates in the next 100 years. As the asteroids are repeatedly observed over the years, scientists refine their estimate of the orbit, and the shrinking margin of error reduces the number of possible dates for an impact. For example, the top item currently has a 1 in 59,000 chance of hitting the earth some time after 2078. This means that that the orbital track is good enough to eliminate the possibility of an impact at any earlier date. Eventually, when no possible impact dates remain in the next 100 years, the object is removed from the table.
Because 2012 DA14 was removed the day after its closest approach, I’m pretty sure what happened is that it came in range of so many telescopes and radar systems that its orbit has been thoroughly pinned down that there was no longer any doubt that it will keep missing the Earth for the next 100 years. Indeed, the Minor Planet Center records 297 observations of the orbit of 2012 DA14 on February 16th alone.
There are still many as-yet-undiscovered near-Earth asteroids out there, some of them probably quite large. It’s possible — arguably inevitable — that one of them will hit us some day. But not 2012 DA14. At least not soon. We know it far too well.