Thursday, January 2, 2014

Small asteroid 2014 AA hit the Earth's atmosphere

M.P.E.C. 2014-A02 issued on 2014 Jan. 2 at 13:08 UT reports the discovery of the asteroid 2014 AA (discovery magnitude 19.1) by Mt. Lemmon Survey (MPC code G96 - Observer R. A. Kowalski) on images taken on January 1.2 with a 1.5-m reflector + CCD. 2014 AA (that is the very first asteroid discovered in 2014) had an estimated size of 1.7 m - 3.8 m (based on the object's absolute magnitude H=30.9).

As reported on this MPEC:
It is virtually certain that 2014 AA hit the Earth's atmosphere on 2014 Jan. 2.2 +/- 0.4, as demonstrated by independent calculations by Bill Gray, the MPC and Steve Chesley (JPL).  According to Chesley, the impact locations are widely distributed, most likely falling on an arc extending from Central America to East Africa, with a best-fit location just off the coast of West Africa on Jan. 2.10.  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.

Below you can see one of the discovery images of 2014 AA. The asteroid is the streak just left of center, surrounded by the purple circle.

Courtesy of Catalina Sky Survey / NASA

Below you can see the two maps of the possible impact region made by Bill Gray. (click on the images for a bigger version)

These maps are based on half-arcsecond Monte Carlo noise. The corresponding impact times and locations are listed here.

The animation below made by Pasquale Tricarico shows the Earth as observed from the asteroid 2014 AA, using the nominal orbit solution. In the background are visible the Sun and the Moon. The asteroid approaches the Earth from the night side, and enters Earth's shadow cone at approximately 01:45 UT of January 2, approximately 40 minutes before entering the Earth's atmosphere. (click on it for a bigger version).

According to NASA/JPL "so far, there have been a few weak signals collected from infrasound stations in that region of the world that are being analyzed to see if they could be correlated to the atmospheric entry of 2014 AA."

This is only the second time in history that an  impacting object is observed prior to atmospheric entry. The first time it happened was with asteroid 2008 TC3. For more info about 2008 TC3 see our 2008 posts here:

UPDATE - January 03, 2014

Below an animation made out of the discovery images of asteroid 2014 AA. It was taken between 0618 and 0646 UT of January 1, 2014. The slight "streaking" of the asteroid in the image is due to its rapid motion across the background of stars as it approached the Earth. The brightness of the asteroid was around magnitude 19 at the moment of its discovery.

Courtesy of Catalina Sky Survey / NASA

Infrasound records analyzed by Peter Brown of the University of Western Ontario suggest an impact energy between 500 and 1,000 tons of TNT. Three infrasound stations detected very weak signals that were used to pinpoint the location of the energetic explosion. Triangulation by Brown using those records, shown in the graphic below, indicates that 2014 AA finished its race into the atmosphere likely near 40° west, 12° north (about 3,000 km east of Caracas, Venezuela, over the Atlantic). Read more about this here on S&T.

Courtesy Peter Brown

UPDATE - January 04, 2014

Trajectory of asteroid 2014 AA before impact. The blue dot is Earth and the green line represents the asteroid’s trajectory, with small green dots spaced ~1 hour apart. (click on the image for a bigger version)


by Ernesto Guido

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