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An unusual asteroid traveling close to Earth is believed to be a piece of the moon, but exactly how it ended up making its way through the solar system remains a mystery. Now, researchers say they have made a fundamental connection in this cosmic puzzle.
The space rock, known as 2016 HO3, is a rare quasi-satellite – a type of near-Earth asteroid that orbits the Sun but is close to our planet.
Astronomers first discovered it in 2016 using the Pan-STARRS, or Panoramic Survey Telescope and Rapid Response System, telescope in Hawaii. Scientists call the asteroid Kamo’oalewa, a name derived from a Hawaiian creation song that alludes to an offspring traveling alone.
Although most near-Earth asteroids originate from the main asteroid belt – between the orbits of Mars and Jupiter – new research has revealed that Kamo’oalewa likely came from the crater Giordano Bruno on the far side of the Moon, or on the side opposite to of the Moon. Earth, according to a study published on April 19 in the journal Nature Astronomy.
It’s the first time astronomers have traced a potentially dangerous near-Earth asteroid to a lunar crater, said study lead author Yifei Jiao, a visiting researcher at the University of Arizona Lunar and Planetary Laboratory and a doctoral student at Tsinghua University in Beijing.
“This was a surprise, and many were skeptical that it could come from the Moon,” study co-author Erik Asphaug, a professor at the University of Arizona laboratory, said in a statement. “For 50 years we have studied rocks collected by astronauts from the surface of the Moon, as well as hundreds of small lunar meteorites that were randomly ejected by asteroid impacts from all over the Moon that ended up on Earth. Kamo’oalewa is a kind of missing link that connects the two.”
In addition to helping confirm Kamo’oalewa’s potential relationship with the Moon, the discoveries could lead to other revelations – including how the ingredients for life arrived on Earth.
Once upon a time there was a crater
Measuring between 46 and 58 meters in diameter, Kamo’oalewa is about half the size of London eye Ferris wheel. During its orbit, it comes within 14.5 million kilometers of Earth, making it a potentially dangerous asteroid that astronomers will track and learn more about if it gets too close to our planet.
Previous research has focused on the asteroid’s reflectivity, which, unlike typical near-Earth asteroids, is similar to lunar materials, as well as the space rock’s low orbital speed relative to Earth, a quality that suggests it came from relatively close range.
For the new study, astronomers used simulations to identify which of the Moon’s thousands of craters could have been the asteroid’s point of origin.
Based on modeling, the team determined that the impactor that potentially created the asteroid would need to be at least 1 kilometer in diameter to dislodge such a large fragment. When the object hit the Moon, it likely excavated Kamo’oalewa beneath the lunar surface, sending the space rock flying and leaving a crater more than 10 to nearly 20 kilometers across.
These simulations also helped the team look for a relatively young crater, given that the asteroid is estimated to be just a few million years old, while the moon is believed to be 4.5 billion years old.
These parameters helped researchers identify Giordano Bruno, a 22-kilometer-wide crater estimated to be 4 million years old, as the likely location where Kamo’oalewa began his journey.
The anatomy of an impact
The study’s simulations showed that Kamo’oalewa was carved into the lunar surface at several kilometers per second.
“You would think that the impact event would pulverize and distribute the (lunar material) everywhere,” Asphaug said. “But there it is. So we solve the problem and ask ourselves, ‘How can we make this happen?’”
Based on their models, the team believes the impact event sent tens of hundreds of 10-meter (32.8-foot) fragments into space. However, Kamo’oalewa survived as a huge, singular fragment.
“Although most of this debris impacted Earth as lunar meteorites over less than a million years, a few lucky objects may survive in (Sun-centered) orbits as near-Earth asteroids, yet to be discovered or identified,” Jiao said.
Understanding how such a giant chunk of the Moon could remain intact long enough to become an asteroid could help scientists studying panspermia, or the idea that the ingredients for life may have been delivered to Earth as “organic hitchhikers” on rocks. space, such as asteroids, comets or other planets.
“Although Kamo’oalewa comes from a lifeless planet, it demonstrates how rocks ejected from Mars could contain life – at least in principle,” Asphaug said.
Kamo’oalewa Specimen: A Connecting Puzzle Piece
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 opens the way to gaining real knowledge about the damage that asteroid impacts can cause to planetary bodies,” said study co-author Renu Malhotra, professor of planetary sciences at the University of Arizona, in a statement.
The Chinese Tianwen-2 mission, scheduled to launch in 2025, will visit Kamo’oalewa with the aim of collecting samples from the asteroid and eventually returning them to Earth.
“It will be different in important ways from any of the specimens we have so far – one of those connecting pieces that helps solve the puzzle,” Asphaug said.
Studying a sample excavated from the far side of the Moon could reveal information about a part of the Moon that has been less studied and shed light on the composition of its subsurface. Given that the impact likely happened a few million years ago – relatively young on astronomical timescales – the samples could also help scientists study how space radiation causes wear and erosion on asteroids over time.
“The interesting thing is that when a space mission visits an asteroid and returns some samples, we get surprises and unexpected results, which often go beyond what we expected,” said study co-author Dr. Patrick Michel, astrophysicist and director of research at the Center French National Institute of Scientific Research. “So whatever Tianwen-2 returns, it will be an extraordinary new source of information, like all asteroid missions so far.”
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 project scientist for both the Lunar Reconnaissance Orbiter and Artemis III. Petro was not involved in the study.
The hope is that future samples can confirm Kamo’oalewa’s lunar origin.
“Going out there and finding out is absolutely one way to do it now,” Petro said. “It’s a great 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, no other planet in our solar system with a moon like ours. And things like this are great reminders of how special the Earth-Moon system is.”
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