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An unusual asteroid traveling near Earth is thought to be a piece of the moon, but how it came to zoom through the solar system is a mystery. Now, researchers say they have made an important link in this cosmic puzzle.
The space rock, known as 2016 HO3, is a rare model satellite – a type of near-Earth asteroid that orbits the sun but sticks close to our planet.
It was first discovered by astronomers in 2016 using the Pan-STARRS, or Pan-Star Survey Telescope and Rapid Response System, telescope in Hawaii. Scientists call the asteroid Kamo’oalewa, a name derived from a Hawaiian creation chant that mentions an offspring traveling alone.
Although most near-Earth asteroids come from the main asteroid belt – between the orbits of Mars and Jupiter – new research has shown that Kamo’oalewa is more likely to have come from the Giordano Bruno crater on the side of the moon, or from the side face away from him. Earth, according to a study published April 19 in the journal Nature Astronomy.
This is the first time astronomers have found a near-Earth asteroid that could be hazardous to a lunar crater, said lead study author Yifei Jiao, a visiting scholar at the University of Arizona’s Lunar Laboratory and Planetarium and doctoral student at Tsinghua University in Beijing.
“This was surprising, and many were skeptical that it could come from the moon,” study author Erik Asphaug, a professor at the University of Arizona’s lab, said in a statement. “For the past 50 years we have been studying rocks collected by astronauts on the surface of the moon, as well as hundreds of small lunar meteorites randomly ejected by asteroid impacts from all over the moon that ended up on Earth. Kamo’oalewa is kind of the missing link that connects the two.”
As well as helping to confirm Kamo’oalewa’s possible relationship to the moon, the findings could eventually lead to other revelations – including how the ingredients of life made their way to Earth.
Once on a crater
Measuring between 150 and 190 feet (46 and 58 meters) in diameter, Kamo’oalewa is about half the size of the London Eye Ferris wheel. During its orbit, it comes within 9 million miles (14.5 million kilometers) of Earth, making it a potentially hazardous asteroid that astronomers keep an eye on and learn about in case it passes too close to us. ever planet.
Previous research has focused on the asteroid’s reflectivity, which is unlike typical near-Earth asteroids that resemble lunar materials, as well as the space rock’s low orbital velocity relative to Earth, a quality that suggests it came from a relatively distant location. nearby.
For the new study, astronomers used simulations to narrow down which of the moon’s thousands of craters could be the asteroid’s point of origin.
Based on the modeling, the team determined that the impactor would have been at least 0.6 miles (1 kilometer) in diameter to cause the asteroid to release such a large fragment. When the object hit the moon, it likely dug Kamo’oalewa out from under the moon’s surface, sending the space rock flying and leaving a crater more than 6 to 12 miles (10 to nearly 20 kilometers) in diameter.
These simulations helped the team search for a relatively young crater, since the asteroid is estimated to be only a few million years old, while the moon is believed to be 4.5 billion years old.
These parameters helped researchers zero in on Giordano Bruno, a 14-mile-wide (22-kilometer-wide) crater estimated to be 4 million years old, as the likely location where Kamo’oalewa began his journey.
The anatomy of affect
The study’s simulations showed that Kamo’oalewa was excavated from the lunar surface at several miles per second.
“You would think that the impact event would have pulverized the (lunar material) and distributed it far and wide,” Asphaug said. “But yes. So we turned the problem around and asked ourselves, ‘How can we make this happen?'”
Based on their models, the team believes the impact event sent thousands of 32.8-foot (10-meter) fragments flying into space. But Kamo’oalewa lived on as a huge, singular fragment.
“While most of that debris would impact Earth as lunar debris for less than a million years, a lucky few can survive in (heliocentric) orbit as near-Earth asteroids, which have yet to be found or to be recognized,” Jiao said.
Understanding how a huge chunk of the moon could have survived long enough to become an asteroid could help scientists studying panspermia, or the idea that the ingredients for life may have been delivered to the Earth as “organic hitchhikers” on space rocks such as asteroids, comets. or other planets.
“Even though Kamo’oalewa comes from a lifeless planet, it shows how rocks ejected from Mars could harbor life – at least in principle,” Asphaug said.
Kamo’oalewa specimen: A connected puzzle piece
Studying crater impacts on the moon can also help scientists better understand the consequences of asteroid impacts should a space rock threaten Earth in the future.
“Testing the new model of Kamo’oalewa’s origin from a particular young lunar crater paves the way for ground-based knowledge of the damage asteroid impacts can do to planetary bodies,” said study coauthor Renu Malhotra, professor of planetary sciences at the University of Arizona, in a statement.
China’s Tianwen-2 mission, launching in 2025, will visit Kamo’oalewa with the aim of collecting samples from the asteroid and eventually returning them to Earth.
“It’s going to be different in important ways from any of the specimens we’ve had so far — one of those connecting pieces that helps you solve the puzzle,” Asphaug said.
Studying a sample excavated from the far side of the moon could reveal insights into a little-studied part of the moon and shed light on the composition of its subsurface. Since the impact likely occurred a few million years ago — relatively young on astronomical time scales — the samples could help scientists study how space radiation causes weathering and erosion of asteroids with passage of time.
“The exciting thing is that when a space mission visits an asteroid and brings back samples, we get surprises and unexpected results, which go beyond what is normally expected,” said the study’s co-author , Dr Patrick Michel, astrophysicist and director of research at the Centre. The National Center for Scientific Research in France. “So whatever Tianwen-2 brings back, it will be a source of extraordinary new information, like every asteroid mission to date.”
For a long time, astronomers thought it was impossible for meteorites to come from the moon until lunar meteorites were found on Earth, said Noah Petro, NASA’s project scientist for the Lunar Reconnaissance Orbiter and Artemis III. Petro was not involved in the study.
It is hoped that future samples may confirm the origin of Kamo’oalewa’s moon.
“It’s a whole way to get there and find out now,” Petro said. “It’s a great reminder that we live in a very exciting solar system and that we live in a very exciting corner of the solar system with our moon. There is no other place, no other planet in our solar system with a moon like ours. And things like this are great reminders of how special the Earth’s Moon system is.”
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