[meteorite-list] Asteroid 2014 AA 'Virtually Certain' to Have Harmlessly Impacted Earth

[Ron Baalke]

http://www.slate.com/blogs/bad_astronomy/2014/01/02/asteroid_2014_aa_harmless_impact_over_atlantic_ocean_last_night.html

Tiny Asteroid Discovered Just Yesterday “Virtually Certain” to Have Harmlessly 
Impacted Earth
By Phil Plait
Jan 2, 2014

For just the second time in history, an asteroid was discovered before 
it impacted the Earth. Don't panic: It was very small, probably just a 
few meters across, and burned up harmlessly in our atmosphere. But after 
events of the past year, it underscores the need to keep our eyes open.

The asteroid is (well, was) named 2014 AA, the very first asteroid discovered 
this year. It was detected by the Mount Lemmon Survey using a 150 centimeter 
(60 inch) telescope located on a mountaintop in Arizona. The first image 
showing the asteroid was taken on Jan. 1, 2014, at about 06:20 UTC (01:20 
EST) - telescopes work whenever the sky is clear, holidays or no. The 
rock was faint, at about magnitude 19; the faintest star you can see with 
your naked eye is 150,000 times brighter! But an orbital calculation showed 
it was very close to Earth, and getting closer.

In fact, as the Minor Planet Electronic Circular discovery announcement 
said, "It is virtually certain that 2014 AA hit the Earth's atmosphere 
on 2014 Jan. 2.2 +/- 0.4" - meaning around 05:00 UTC Jan. 2, midnight 
EST, just a few hours ago. It most likely burned up over the Atlantic, 
somewhere between South America and Africa.

>From its brightness, it was probably about two to four meters across, 
about the size of a car. Objects that small generally disintegrate as 
they ram through the Earth's atmosphere at high speed, so there was never 
any big danger from this object. It orbited the Sun on a path that took 
it just outside the orbit of Mars to just inside our own. [UPDATE (Jan. 
2 at 18:00 UTC): I had originally written the asteroid was less than two 
meteres across, but astronomer Ron Baalke informed me that it was more 
like two to four meters across judging from its brightness, so I have 
updated the post here.]

It's only the second time in history that an asteroid was seen before 
it hit us; the first was 2008 TC3, which burned up over Sudan in Africa 
in 2008. That one was also discovered just a day before atmospheric entry. 
Other rocks have been discovered in the past that gave us a very close 
shave, and usually small asteroids that actually hit us go undetected 
until someone looks up and sees them! That's because they are so small: 
That makes them faint and hard to detect. Because they are close by they 
also tend to move very rapidly across the sky, making them harder to find. 
The 19-meter wide asteroid that blew up over Russia last year was undetected 
until it hit, for example.

It's possible some satellites may have observed the entry of 2014 AA, 
and hopefully we'll get an image or two. Stay tuned.

And of course this underscores how seriously we need to take asteroid 
impacts. While 2014 AA wasn’t a threat, there are a million bigger rocks 
out there that cross Earth's orbit, big enough to cause real damage should 
they hit us. And given enough time, they will.

That's why we need to keep scanning the skies, locating and characterizing 
these asteroids. Both NASA and the B612 Foundation are working on better 
detection methods, but that's only the first step; we also need a plan 
in place should we find one with our number on it. B612 is working on 
that, but we're a long way from being able to implement it.

As usual, let me say that you shouldn't run around in circles panicking 
over this; after all, these are rare events. But if we do nothing at all, 
we're guaranteeing that a big impact will occur sometime in the future. 
Like so many problems, the cost of prevention is small compared to the 
cost of doing nothing. We can afford the former, but not the latter.