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An unusual asteroid traveling near Earth is believed to be part of the moon, but exactly how it zoomed through 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: a type of asteroid that is near Earth and 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, a name derived from a Hawaiian creation song that refers to 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 revealed that Kamo’oalewa most likely originated from the Giordano Bruno crater on the far side of the moon, or the side that faces away from the Earth. Earth, according to a study published 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 lead study 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 were skeptical that it could come from the moon,” co-author Erik Asphaug, a professor at the University of Arizona laboratory, said in a statement. “For fifty years we have been studying rocks collected by astronauts from the moon’s surface, as well as hundreds of small lunar meteorites that are randomly thrown from all over the moon by asteroid impacts and end up on Earth. Kamo’oalewa is kind of a missing link that connects the two.”
In addition to helping confirm Kamo’oalewa’s potential relationship with the moon, the findings could ultimately lead to other revelations, including how the ingredients for life made their way to Earth.
Once upon a time there was a crater
With a diameter of between 46 and 58 meters, Kamo’oalewa is about half the size of the London Eye Ferris wheel. During its orbit, it comes within 9 million miles of Earth, making it a potentially dangerous asteroid that astronomers are monitoring and learning more about in case it ever comes too close to our planet .
Previous research focused on the asteroid’s reflectivity, which unlike typical near-Earth asteroids is comparable to lunar materials, and on the space rock’s low orbital velocity relative to Earth, a quality that suggests it is of relatively came close.
For the new study, astronomers used simulations to figure out which of the thousands of craters on the moon might have been the asteroid’s point of origin.
Based on the models, the team determined that the impactor that may have created the asteroid would have to be at least 1 kilometer in diameter to dislodge such a huge fragment. When the object hit the moon, it likely dug Kamo’oalewa beneath the moon’s surface, sending the space rock flying and leaving a crater more than 10 to nearly 20 kilometers in diameter.
These simulations also helped the team search for a relatively young crater, as 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 identify Giordano Bruno, a 14-mile-wide crater estimated to be 4 million years old, as the likely spot where Kamo’oalewa began its journey.
The anatomy of an impact
The study’s simulations showed that Kamo’oalewa was being excavated from the moon’s surface at a speed of several kilometers per second.
“You would think the impact event would pulverize and scatter the (lunar material) far and wide,” Asphaug said. “But there 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 event blasted tens of hundreds of 10-meter fragments into space. Yet Kamo’oalewa survived as a huge, single fragment.
“While most of that debris would have impacted Earth as lunar meteorites over the course of less than a million years, a few lucky objects in (sun-centric) orbits may survive as near-Earth asteroids, which have yet to be discovered or identified. Jiao said.
Understanding how such a gigantic portion of the moon could remain intact enough to become an asteroid could help scientists study panspermia, or the idea that the ingredients for life may have been delivered to Earth as “organic hitchhikers’ on space rocks such as asteroids and comets or other planets.
“Although 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 connecting 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 specific, young lunar crater paves the way for gaining ground truth knowledge about the damage that asteroid impacts can cause to planetary bodies,” said co-author Renu Malhotra, professor of planetary sciences at the University of Arizona, in a statement.
China’s Tianwen-2 mission, set to launch in 2025, will visit Kamo’oalewa with the aim of collecting samples of the asteroid and eventually returning them to Earth.
“It will be different in important ways from all the ones we have so far – one of those connecting pieces that help you solve the puzzle,” Asphaug said.
Studying a sample unearthed from the far side of the moon could provide insights into a part of the moon that has been less studied and shed light on the composition of the subsurface. Given that the impact likely occurred a few million years ago — relatively young on astronomical timescales — the samples could also help scientists study how space radiation causes weathering and erosion on asteroids over time.
“The exciting thing is that when a space mission visits an asteroid and returns some samples, we encounter surprises and unexpected outcomes, usually beyond what we expected,” said study co-author Dr. Patrick Michel, astrophysicist and research director at the National Center for Scientific Research in France. “So whatever Tianwen-2 returns will be an extraordinary new source of information, like all asteroid missions 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, says Noah Petro, NASA project scientist for both the Lunar Reconnaissance Orbiter and Artemis III. Petro was not involved in the investigation.
The hope is that future samples can confirm Kamo’oalewa’s origins on the moon.
“Going there and finding out is definitely a way to handle it now,” Petro said. “It’s a great, great reminder that we live in a very exciting solar system and that we live in a very exciting corner of the solar system along with our moon. There is no other place, no other planet in our solar system with a moon like our moon. And things like this are a good reminder of how special the Earth-moon system is.”
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