These meteorites landed on Earth after a 22-million-year voyage
Published Wednesday, April 28, 2021 10:22AM EDT
For the first time, scientists have been able to precisely map the flight path of an asteroid that landed on Earth and trace it back to its point of origin. The boulder-size fragment's journey to our planet began 22 million years ago, according to new research.
The asteroid, known as 2018 LA, appeared like a fireball in the skies over Botswana on June 2, 2018, before breaking apart and landing in the Central Kalahari Game Reserve.
Prior to breaking up in Earth's atmosphere, scientists determined that the asteroid was about 1.7 metres in diameter, weighed 5,700 kilograms and had been travelling at 60,000 kilometres per hour.
"As the asteroid broke up 27 km above ground, it was 20,000 times brighter than the full moon," said Christian Wolf, study coauthor and associate professor from the Australian National University's Research School of Astronomy and Astrophysics, in a statement.
The study published last week in the journal Meteoritics and Planetary Science.
Researchers were able to locate the fragments, called meteorites, and study them. Their findings provide new insights into the history of our solar system.
TRACING AN ASTEROID
The asteroid was discovered to be on an impact trajectory with Earth on June 2, 2018, and eight hours after it was detected, it appeared over South Africa with a flash.
The asteroid was first spotted by the University of Arizona's Catalina Sky Survey, appearing like a faint dot of light zipping among the stars. The astronomical survey is part of NASA's Planetary Defense program and searches for asteroids approaching Earth.
"Small meter-sized asteroids are no danger to us, but they hone our skills in detecting approaching asteroids," said Eric Christensen, study coauthor and director of the Catalina Sky Survey program, in a statement.
Peter Brown, professor and Canada Research Chair in Planetary Small Bodies at Western University in Ontario, worked with the Western Meteor Group to analyze sound waves from the fireball as it crossed into Earth's atmosphere.
The asteroid had one-30th of the energy of the atomic bomb that was dropped on Hiroshima during the Second World War.
"The infrasound shockwave measured in South Africa was not as strong as expected from U.S. Government sensor detections of the bright light," Brown said in a statement.
Data from the Catalina Sky Survey, as well as ANU's SkyMapper telescope in New South Wales, were able to map the asteroid's journey to Earth.
This is only the second time scientists have been able to observe an asteroid in space before it impacted Earth. The first was asteroid 2008 TC3 in Sudan 10 years earlier, according to Peter Jenniskens, lead study author and meteor astronomer at the SETI Institute and NASA's Ames Research Center.
"I could hardly believe my eyes when I came upon a little object that appeared to be moving across images taken by SkyMapper," said Christopher Onken, study coauthor and ANU SkyMapper project scientist and astronomer, in a statement.
"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."
METEORITES AMONG THE WILDLIFE
Data from multiple astronomical observations, along with video recorded of the fireball, helped researchers determine the meteorites had fallen in the Central Kalahari Game Reserve, where wildlife like leopards and lions live.
The Botswana Department of Wildlife and National Parks and the country's Department of National Museum and Monuments helped the researchers search and stay safe in their quest to locate the fragments.
On the last day of the search, Lesedi Seitshiro from the Botswana International University of Science and Technology found the first one. It weighed 18 grams and was only about three centimetres in size.
"The meteorite is named 'Motopi Pan' after a local watering hole," said Mohutsiwa Gabadirwe, study coauthor and geoscientist at the Botswana Geoscience Institute, in a statement. "This meteorite is a national treasure of Botswana."
Gabadirwe is now the curator of the Motopi Pan meteorite.
The researchers uncovered a total of 23 fragments within a few months of the event.
The asteroid's path was traced back to Vesta, the second-largest asteroid in our solar system. It's "the only one bright enough to be sometimes visible to the unaided eye," Onken said.
Vesta's Veneneia basin was created by an impact, and the 2018LA asteroid was a chunk of Vesta that went hurtling into space when this impact happened, according to the researchers.
Motopi Pan belongs to a group of Howardite-Eucrite-Diogenites meteorites, so named due to their composition, that came from Vesta, which is located in the inner part of the asteroid belt between Mars and Jupiter.
Some of the oldest known materials from Vesta and the meteorites include Zircon mineral grains that date to more than 4.5 billion years ago, back to the birth of our solar system.
"Combining the observations of the small asteroid in space with information gleaned from the meteorites shows it likely came from Vesta, second largest asteroid in our Solar System and target of NASA's DAWN mission," Jenniskens said. "Billions of years ago, two giant impacts on Vesta created a family of larger, more dangerous asteroids. The newly recovered meteorites gave us a clue on when those impacts might have happened."
Analysis of the meteorite revealed it was once buried beneath the surface of Vesta. This also helped researchers date that the Veneneia basin likely formed about 4.2 billion years ago.
Another expedition in 2020 revealed an additional Motopi Pan meteorite, and it's the largest fragment to date, weighing in at 92 grams. Researchers are eager to see whether it contributes more to Vesta's story.
Understanding the connections between meteorite fragments and the asteroids they came from is tricky. While scientists understand the current locations and sizes of about one million asteroids today, they don't know their compositions. Meanwhile, they understand what meteorites are made of, but they don't know where most of them came from before they crashed into Earth.
"That in essence is what we are trying to solve: matching meteorites types to asteroid types. Tracing back all the way to a likely crater, it is a bit like looking for clues for a murder that happened 22 million years ago and trying to understand what happened," said Hadrien Devillepoix, study co-author and astronomer at Curtin University in Australia.
"Every time we recover a fresh meteorite with an associated orbit, we slowly map the composition of the asteroid belt. The more of these we get, the better this map gets."