2014 has started off with fireworks! The first designated asteroid of the year, discovered only half an hour before midnight on New Year’s Eve (Tucson local time) but 6.5 hours into 2014 in Universal (or Greenwich Mean) time by Richard Kowalski of the Mount Lemmon Survey, was an Earth impactor.
Based on 7 astrometric measurements taken over the course of 70 minutes, the Minor Planet Center’s orbit has determined that 2014 AA impacted the Earth around Jan. 2.2 +/- 0.4 UT somewhere along an arc stretching from the eastern Pacific Ocean, southern Nicaragua, Costa Rica, very northern Columbia and Venezuela, a long stretch of the Atlantic Ocean and the African countries of Senegal, Gambia, Mali, Burkina Faso, Niger, Chad and Sudan. Maps of the possible impact points have been produced by Bill Gray and can be found here and here. The most likely impact point is in the Atlantic Ocean off the coast of western Africa.
With an absolute magnitude of ~30.9, 2014 AA was likely a very small asteroid with a diameter on the order of 1-5 meters. Such an object would have posed no danger to the ground though small meteorites may have survived passage through the atmosphere. If it fell in the ocean there is a good chance that no one directly witnessed it though the signature of its resulting fireball may be found in weather satellite images.
This marks the second time that an asteroid was detected in space prior to impact. The first impactor, 2008 TC3, was also found by Rich Kowalski and the Mount Lemmon 1.5-m reflector. That body was observed to fall over northern Sudan and led to the recovery of many meteorites (named Almahata Sitta). More on the fall of 2008 TC3 and Almahata Sitta can be found at this blog (here, here, here, and here), the Meteoritical Bulletin and Wikipedia.
Note, that for every small asteroid discovered before hitting the Earth (of which we’ve seen only two) there are many thousands of similar sized objects (and countless smaller ones) that go undetected until seen as brilliant fireballs or meteors. Hopefully planned upgrades to current asteroid surveys such as the Catalina Sky Survey/Mount Lemmon Survey and future surveys like ATLAS will result in more warning time for incoming asteroids.