Meteorite that landed in Botswana tracked to its birthplace in the asteroid belt

Fragment of asteroid 2018 LA recovered in Central Kalahari Game Reserve in central Botswana.
Fragment of asteroid 2018 LA recovered in Central Kalahari Game Reserve in central Botswana. (Image credit: SETI Institute)

A small asteroid barreled through the sky and burned up over the Kalahari Desert of Botswana in the summer of 2018 and now, scientists suspect that the space rock originated from Vesta, the second largest asteroid in the solar system

The small asteroid, named 2018 LA, was first observed through a telescope at the University of Arizona's Catalina Sky Survey and looked like a speck of light whizzing through the stars, according to a statement from the SETI Institute.

"This is only the second time we have spotted an asteroid in space before it hit Earth over land," Peter Jenniskens, a SETI Institute meteor astronomer, said in the statement. "The first was asteroid 2008 TC3 in Sudan 10 years earlier."

Related: The 7 strangest asteroids: Weird space rocks in our solar system 

Mere hours after being spotted, 2018 LA came tumbling out of the sky and burned up in the atmosphere over Botswana, transforming into a brilliant fireball. Remarkably, the SkyMapper Telescope at Australian National University (ANU) captured the moments just before the rock broke through Earth's atmosphere, and CCTV camera footage caught the final moments of the meteor's explosive descent in black-and-white.

"These last images before the asteroid entered Earth's atmosphere were SkyMapper's biggest contribution. They helped to pinpoint both the search area for the meteorite fragments on Earth and the meteor's origin in space," Christopher Onken, the ANU SkyMapper Project Scientist, said in a statement from ANU

Pulling from the available astronomical observations, an international team of scientists pinpointed the region where the meteor likely disintegrated, scattering space rock fragments on the ground below; this region happened to fall within the Central Kalahari Game Reserve, a national park in the Kalahari Desert. 

"The meteorite is named 'Motopi Pan' after a local watering hole," Mohutsiwa Gabadirwe, a geoscientist at the Botswana Geoscience Institute (BGI) in Lobatse, said in the SETI statement.

After searching the park on several field expeditions, the team uncovered 23 fragments of the Motopi Pan meteorite; they then analyzed the isotopes, or versions of elements with different numbers of neutrons, within the meteorite bits. These isotopes hint at the chemical composition and size of the original asteroid, prior to when it burst through the atmosphere.

2018 LA originally measured about 5 feet (1.5 meters) in diameter and had been zooming around in space for about 22 to 23 million years before crash-landing on Earth, the team determined. The rock was traveling about 37,280 mph (60,000 km/h) before entering the planet's atmosphere, according to the ANU statement. 

Further analysis of the rocky fragments showed that they closely resembled another set of meteorites called Sariçiçek that fell in Turkey in 2015.

Both sets of meteorites were categorized as howardite-eucrite-diogenite (HED) meteorites, which are the only class of meteorites to be traced back to Vesta, according to the American Museum of Natural History (AMNH). The bits of eucrite in the HED meteorites contain hardened lava from Vesta's surface; diogenites contain minerals from rocks buried below the surface of the asteroid; and howardites are a unique mix of the two other rock types, formed when objects collided with Vesta.

Related: What's the difference between asteroids, comets and meteors?

"Overall, we classified the material that asteroid 2018 LA contained as being howardite, but some individual fragments had more affinity to diogenites and eucrites," Jenniskens said. The asteroid formed as a breccia, or a cemented mixture of distinct rock pieces that originated from different parts of Vesta. 

"The oldest known materials found in both Vesta and in the meteorite are zircon grains that date back to more than 4.5 billion years ago, during the early phase of the solar system," Onken noted. The orbital path that 2018 LA took around Earth also points to Vesta as the asteroid's origin point, the authors found.

Despite both being HED meteorites, though, Motopi Pan and Sariçiçek differed in several ways. For instance, the team estimated that the material in both meteorites likely solidified on Vesta's surface about 4.563 billion years ago, but phosphate grains in Motopi Pan showed evidence of having melted in more recent history, while Sariçiçek did not bear these markings.

This hinted that Motopi Pan formed close to the center of a large impact event that took place about 4.324 billion years ago, the team concluded. They suspect that the same event formed a giant dent, known as the Veneneia impact basin, on Vesta's surface.

"We now suspect that Motopi Pan was heated by the Veneneia impact, while the subsequent Rheasilvia impact," which occurred later and partially obscures the Veneneia impact basin, "scattered this material around," Jenniskens said.

"Because the team tracked the rock from space all the way down to the impact site, they were able to calculate a very precise orbit that is consistent with an origin near Vesta, providing one of the best links we have between an asteroid and meteorites," Ashley King, a planetary scientist at the Natural History Museum who was not involved in the work, told The Guardian.

The team described their findings in a new study published in the journal Meteoritics and Planetary Science.

Originally published on Live Science.

Nicoletta Lanese
Channel Editor, Health

Nicoletta Lanese is the health channel editor at Live Science and was previously a news editor and staff writer at the site. She holds a graduate certificate in science communication from UC Santa Cruz and degrees in neuroscience and dance from the University of Florida. Her work has appeared in The Scientist, Science News, the Mercury News, Mongabay and Stanford Medicine Magazine, among other outlets. Based in NYC, she also remains heavily involved in dance and performs in local choreographers' work.