For only the second time in history, an asteroid has hit Earth that was discovered hours before impact. But don't panic! The asteroid didn't put a city-sized divot in our planet, it most likely burned up somewhere between Africa and South America over the Atlantic Ocean at midnight EST.
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Asteroid 2014 AA, the first asteroid discovery of the year, was spotted by astronomers using the Mt. Lemmon Survey telescope in Arizona. As shrewdly pointed out by Bad Astronomer Phil Plait, the asteroid was the approximate size of a couch - measuring only a couple of meters across. That's around one-half of a Mini Cooper, whichever takes your fancy. But whatever your preferred size comparison, the outcome was likely the same; the asteroid burned up on atmospheric entry as a meteor.
This might have provided a nice visual spectacle only a day after New Years, but 2014 AA is notable as being the first pre-impact discovery of an asteroid since 2008.
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"2014 AA was unlikely to have survived atmospheric entry intact, as it was comparable in size to 2008 TC3, the only other example of an impacting object observed prior to atmospheric entry," said a Minor Planet Electronic Circular announcement.
In 2008, 2008 TC3 was discovered hours before it disintegrated over Sudan. Knowing the precise time of impact and its approximate geographical location, meteorite hunters were able to find fragments of the fireball strewn over the desert. This was the first time an asteroid had been discovered, impact location predicted and fragments recovered from that location.
Although it's unlikely that fragments from 2014 AA will be recovered from the ground (as the most likely region of reentry was off the western coast of Africa), this is a stunning achievement by asteroid hunters who were able to detect a tiny (and very faint) object approaching Earth and forecast the time and approximate location of impact.
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As we learned from the Russian meteor event nearly a year ago, even comparatively small asteroids can wreak havoc if they slam into the skies over populated regions, so the techniques being developed to detect incoming space rocks could help us prepare - or even evacuate - a city if necessary.
After all, it's not a question of if we'll get hit again, it's a question of when, and near-Earth asteroid surveys are our first line of defense.
Source: Bad Astronomy