Let’s Start 2014 with a Bang! Hello and Goodbye to Asteroid 2014 AA

It was just another typical night dedicated to searching for Near Earth Asteroids at the Mount Lemmon observatory. Well, it was the first day (night) of the year, when most of us might have still been partying, but planetary protection knows naught about anthropocentric or heliocentric celebrations. Up in the 1.5m (60″) telescope was observer Richard “The Impactor Whisperer” Kowalski, discoverer of the only other asteroid, 2008 TC3, to have been observed before entering Earth’s atmosphere (back in October 2008). Shortly after 1:15am on January 1, he imaged an area of the sky where a small streak of light moved quickly against the background stars. Over the next hour or so he imaged that streak a total of 7 times and the positions of the asteroid were reported to us at the Minor Planet Center. We announced this new asteroid some 31 hours after the first observation and designated it 2014 AA, the first asteroid discovered in 2014. It was an NEA. It had already hit us.

This is no way to start a new year!

Luckily it was a very small asteroid, 1-3m across, which almost surely burned up in the atmosphere, with the most that could reach the ground being small fragments. From the initial orbit it was unclear where the precise point of entry into the atmosphere had been. Bill Gray, an asteroid software developer, provided the diagram below showing the possible atmospheric impact points stretching from West of Central America to East Africa:

[UPDATE 4 Jan.: See updated diagram from Bill Gray.]
As can be seen, it stretches about a third of the way across the globe. Later, Peter Brown of the University of Western Ontario, triangulated the impact spot with much tighter constraints based on data from infrasound detectors used by the Comprehensive Nuclear-Test-Ban Treaty Organization to keep tabs on who’s exploding what, where. His best estimate is 2014 AA disintegrated half way over the Atlantic, some 3,000 km East of Caracas, Venezuela, and 1,800 km West of the Cape Verde islands.

Can you imagine what it would’ve been like to ride on 2014 AA as it came towards Earth? No need to imagine because Pasquale Tricarico, of the Planetary Science Institute created this animation to show us:

Given the location of the atmospheric disintegration of 2014 AA, it’s likely it met a lonely death with no witnesses. But even if this had taken place over a populated area, the small size of this asteroid meant it would have put on nothing more than a light show with no audible explosion or shockwave, and certainly no broken windows like the Chelyabinsk meteor of February 15, 2013. The energy of that explosion was estimated at 500 kilotons of TNT, while 2014 AA provided a lowly 500 to 1,000 tons (1/500th to 1/1,000th that of the Chelyabinsk meteor) according to Peter Brown’s estimates.

Let’s not forget that asteroids the size of a car enter the Earth’s atmosphere a few times a year—what’s special about 2014 AA is that we discovered it before it got here. Will we have to wait another 5 years to do it again?