In 2008, a small asteroid fell to Earth in the Namibian Desert, leaving in its wake over 600 meteorites. Their properties and distributions on the ground have now painted a picture of how asteroid 2008 TC3 fragmented. The work suggests that the largest pieces survived because they came from the space rock's backside.
The study, published in Meteoritics and Planetary Science, details the simulation of how the 6-meter (18-foot) asteroid broke apart. The object was observed from 20 hours before it reached Earth to its eventual disintegration through the African sky. The information suggested that the smallish size allowed for a lot of fragments to survive.
"Most of our meteorites fall from rocks the size of grapefruits to small cars," lead author and meteor astronomer Peter Jenniskens of the SETI Institute and NASA Ames Research Center, said in a statement.
"Rocks that big do not spin fast enough to spread the heat during the brief meteor phase, and we now have evidence that the backside survives to the ground."
The hundreds of fragments had quite a wide range of sizes, and were spread over an area of 210 square kilometers (81 square miles) – almost twice the size of Walt Disney World. University of Khartoum professor Muawia Shaddad and his students collaborated with Jenniskens and inspected the area, conducting grid searches perpendicular to the asteroid path.
"In a series of dedicated search campaigns, our students recovered over 600 meteorites, some as big as a fist, but most no bigger than a thumbnail," explained Shaddad. "For each meteorite, we recorded the find location."
The smallest fragments were in a thin slither of the area no wider than 1 kilometer (0.6 miles), while the larger meteorites were spread further afield. A simulation of the melting and final break-up of the asteroid made it clear that the smallest ones were stopped by the friction of the atmosphere, while the bigger ones were able to keep tumbling for longer.
"Because of the high speed coming in, we found that the asteroid punched a near vacuum wake in the atmosphere," theoretical astronomer Darrel Robertson of Asteroid Threat Assessment Project added. "The first fragments came from the sides of the asteroid and tended to move into that wake, where they mixed and fell to the ground with low relative speeds."
"The asteroid melted more and more at the front until the surviving part at the back and bottom-back of the asteroid reached a point where it suddenly collapsed and broke into many pieces," explained Robertson. "The bottom-back surviving as long as it did was because of the shape of the asteroid."
The asteroid was an odd mixture of rocks, suggesting that even at these smaller sizes, an asteroid can be just a pile of rubble stuck together.