A 22 million year journey of the asteroid belt in Botswana


It was a surreal place to go meteorite hunting. Bat-eared foxes and warthogs walked past, lions stealthily stalked and slaughtered giraffes while leopards lounged in the trees. Guardians from Botswana’s Department of Wildlife and National Parks protected the search team in case a fanged predator got too close for comfort. The meteorites also looked a lot like animal droppings, meaning the team were frequently bamboozled by coprological impostors.

“It was a totally unusual experience for all of us,” said Gabadirwe.

It wasn’t until June 23, the last day of the initial search mission, that the first meteorite was discovered – a small piece of stars weighing less than an ounce. It was named Motopi Pan, after a local waterhole. “It has become a national treasure of Botswana, this little rock,” said Dr Jenniskens.

The compositions of the meteorites were compared to those found on Vesta, using data from NASA’s Dawn spacecraft. Orbiting now lifeless around the dwarf planet Ceres after running out of fuel in late 2018, Dawn documented Vesta’s geology from 2011 to 2012. Scientists have corroborated this origin story by reconstructing the asteroid’s earth path.

Cosmic rays imprint traces on asteroids by altering atomic nuclei. The traces on these meteorites suggest that the asteroid that crashed into Earth bathed in this radiation for 22 million years on its journey to Earth. This meant that a 22 million year old impact crater would mark the spot where this asteroid was released from Vesta.

A six-mile-long crater named Rubria on Vesta was the best candidate. The asteroid’s surprising lack of contamination from the solar wind – the flow of plasma and particles from the sun – suggested that the asteroid’s material was protected from space for billions of years. Unlike another crater of the same age, Rubria sat on a hill undisturbed by landslides, a quiet 2018 LA spot could remain buried before an impact frees it.

“The study has it all, in terms of cosmic drama,” said Katherine Joy, a meteorite expert at the University of Manchester in England, not involved in the work. But tying 2018 LA to a specific location on Vesta relies on a lot of underlying assumptions, so no one can be sure Rubria is the right place.

For now, scientists will continue to monitor the skies and explore the deserts of Earth, hoping to find more illuminating fragments of our cosmic cradle’s past. Meteorite hunts “are always amazing adventures,” said Dr Jenniskens – a grueling but exciting way to spend your life.

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