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An unusual asteroid orbiting near Earth is thought to be part of the moon, but exactly how it approached the solar system has remained a mystery. Now researchers say they have made an important connection in this cosmic puzzle.
The space rock known as 2016 HO3 is a rare quasi-satellite; It is a type of near-Earth asteroid that orbits the sun but remains close to our planet.
Astronomers first discovered it in 2016 using the Pan-STARRS telescope, or Panoramic Survey Telescope and Rapid Response System, in Hawaii. Scientists call the asteroid Kamo’oalewa; The name is derived from a creation hymn in Hawaii that refers to a cub traveling on his own.
While most near-Earth asteroids originate from the main asteroid belt between the orbits of Mars and Jupiter, new research found that Kamo’oalewa most likely came from the Giordano Bruno crater on the far side of the moon or the Giordano Bruno crater on the side facing Earth’s far side. Earth, according to a study published April 19 in the journal Nature Astronomy.
It’s the first time astronomers have traced a potentially hazardous near-Earth asteroid to a lunar crater, said the study’s lead author, Yifei Jiao, a visiting scholar at the University of Arizona’s Lunar and Planetary Laboratory and a doctoral student at Tsinghua University in Beijing.
“This was a surprise, and many people were skeptical that it could come from the moon,” Erik Asphaug, a professor in the University of Arizona laboratory and one of the study’s authors, said in a statement. “For 50 years, we have been studying rocks collected on the surface of the moon by astronauts, as well as hundreds of small lunar meteorites randomly ejected by asteroid impacts from all over the moon and reaching Earth. Kamo’oalewa is sort of the missing link that connects the two.”
In addition to helping confirm Kamo’oalewa’s potential relationship with the moon, the findings may ultimately lead to other explanations — including how the ingredients necessary for life reach Earth.
Once upon a time a crater
At 150 to 190 feet (46 to 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 are tracking and learning more about if it comes too close to our planet.
Previous research has focused on the reflectivity of the asteroid, which resembles lunar materials unlike typical near-Earth asteroids, as well as the space rock’s low orbital speed relative to Earth; a quality that suggested he came from a relatively nearby place.
For the new study, astronomers used simulations to narrow down which of the moon’s thousands of craters might have been the asteroid’s origin point.
Based on modeling, the team determined that the impactor that potentially created the asteroid would have to be at least 0.6 miles (1 kilometer) in diameter to dislodge such a large piece. When the object hit the moon, it blew up the space rock, possibly excavating Kamo’oalewa from beneath the lunar surface, leaving a crater more than 6 to 12 miles (10 to about 20 kilometers) in diameter.
These simulations also helped the team search for a relatively young crater; While the asteroid is estimated to be only a few million years old, 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 spot where Kamo’oalewa began its journey.
Anatomy of a blow
The study’s simulations showed that Kamo’oalewa was being excavated from the lunar surface at speeds of several miles per second.
“You would think that the impact event would pulverize (the lunar material) and disperse it over a wide area,” Asphaug said. “But here it is. So we turned the problem around and asked ourselves: ‘How can we make this happen?’”
Based on their models, the team believes the impact caused tens to hundreds of 32.8-foot (10-meter) pieces to fly into space. But Kamo’oalewa survives as a huge, singular piece.
“Although most of this debris hit Earth as lunar meteorites less than a million years ago, a few lucky objects that have not yet been discovered or identified may survive in (heliocentric) orbits as near-Earth asteroids,” Jiao said.
Understanding how such a large chunk of the Moon could have remained intact enough to become an asteroid is a challenge for scientists studying panspermia, or the idea that materials essential to life may have been delivered to Earth as “organic hitchhikers” on space rocks such as asteroids and comets. might help. or other planets.
“Although Kamo’oalewa comes from a lifeless planet, it shows how rocks ejected from Mars could, at least in principle, support life,” Asphaug said.
Kamo’oalewa example: A puzzle piece that connects
Studying crater impacts on the Moon could also help scientists better understand the consequences of asteroid impacts if a space rock poses a threat to Earth in the future.
“Testing the new model of Kamo’oalewa’s origin from a specific, young lunar crater paves the way to obtain ground-truth information about the damage that asteroid impacts can cause to planetary bodies,” said study co-author Renu Malhotra, professor of planetary sciences. In a statement from the University of Arizona.
China’s Tianwen-2 mission, starting in 2025, will visit Kamo’oalewa with the aim of collecting samples from the asteroid and eventually returning them to Earth.
“This will be different in important ways from the examples we’ve had so far; it’s one of the connecting pieces that will help you solve the puzzle,” Asphaug said.
Examining a sample excavated from the far side of the Moon could reveal insights into a less-studied part of the moon and shed light on the composition of its subsurface. Given that the impact likely occurred several million years ago (relatively young on astronomical time scales), the samples could also help scientists study how space radiation causes weathering and erosion on asteroids over time.
Co-author of the study, astrophysicist and research director Dr. “The exciting thing is that when a space mission visits an asteroid and returns some samples, we often encounter surprises and unexpected results that go beyond what we expected,” said Patrick Michel. National Center for Scientific Research in France. “So whatever Tianwen-2 returns, like all asteroid missions to date, it will be an extraordinary source of new information.”
Noah Petro, NASA’s project scientist for both the Lunar Reconnaissance Orbiter and Artemis III, said that for a long time, astronomers thought it was impossible for meteorites to come from the moon until lunar meteorites were found on Earth. Petro was not involved in the research.
It is hoped that future samples can confirm Kamo’oalewa’s lunar origin.
“Going out there and learning about it is definitely a way to do it now,” Petro said. “It’s a very, very nice reminder that we live in a very exciting solar system, and we live in a very exciting corner of the solar system with our moon. There is no other place or planet in our solar system that has a satellite similar to our moon. “And things like this are a reminder of how special the Earth-moon system is.”
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