The space is vast and wonderful. It is perfectly understandable, therefore, that a small rock decides to accompany the Earth and Moon in their annual circumnavigation of the Sun.
This rock, 50 meters long, was discovered in 2016 by the Pan-STARRS 1 asteroid hunter telescope in Hawaii (USA). The Hawaiian name of this eccentric entity, (469219) Kamo’oalewa, means “rocking celestial object.”
While circling Earth repeatedly, this timid body never gets closer than 14 million kilometers, which is 38 times farther than the Moon. It comes 40 million kilometers away before returning for a closer rendezvous.
Calculations of this orbital waltz indicate that it began tracking our planet relatively stably about a century ago, and will continue its pirouettes around Earth for several centuries to come.
But where did Kamo’oalewa come from? It is difficult to study the object with telescopes because of its small dimensions and its tendency to hide in shadows.
But in a paper published on Thursday in “Communications Earth & Environment,” a team of scientists reported that they may have solved the mystery. By observing Kamo’oalewa for brief moments when it was lit by the Sun, astronomers discovered that it appears to be made of the same kind of frozen magmatic matter found on the lunar surface.
“My first reaction to the observations in 2019 was that I had probably made a mistake,” said Benjamin Sharkey, a graduate student at the University of Arizona and lead author of the study.
Kamo’oalewa was expected to be composed of minerals commonly found in asteroids. But new observations this spring have made it clear that “data doesn’t care what we think,” said Sharkey. Kamo’oalewa does look like a very small version of the Moon. In making this discovery, he said, “I was both excited and confused.”
Based on its orbit and composition, Kamo’oalewa could be a fragment of the Moon, ripped off by a meteor impact in the past.
Kamo’oalewa may look like a miniature Moon, but it isn’t. Unlike the Moon, which is gravitationally bound to Earth, Kamo’oalewa is gravity bound to the Sun. If the Earth were to suddenly disappear, Kamo’oalewa would continue its orbit around our star. This is what is known as a quasi-satellite. Astronomers know of four others near Earth, but Kamo’oalewa has the most stable orbit.
In April 2017, Kamo’oalewa was well lit when the Earth came between the near-satellite and the Sun. Astronomers observed it with two telescopes in Arizona —the Large Binocular Telescope and the Lowell Discovery Telescope—and used reflected light to identify your minerals.
They’ve seen many silicates, minerals found in rock bodies throughout the solar system, and later observations have confirmed that Kamo’oalewa’s silicates look a lot like those found on the Moon.
It could be a coincidence, and so the study authors suggested other possible origin stories: Kamo’oalewa could be a captured asteroid with a composition similar to that of the Moon, or a fragment of an asteroid destroyed by the gravitational pull of the Earth-system. Moon.
The team’s data, however, “further support the lunar origin,” said Hannah Sargeant, a planetary scientist at the University of Central Florida, who was not involved in the study.
This quasi-satellite may not be alone: ​​the orbits of three other near-Earth objects are close enough to Kamo’oalewa’s to suggest that they may all have come from the same cataclysmic event. But today “there is still not enough evidence to confidently state how these objects originated,” Sargeant said.
“The only way to be sure is to send a spacecraft to this little body,” said Paul Byrne, a planetary scientist at Washington University in St. Louis, who was not involved in the study. In that case, China’s space agency plans to land on it and collect samples and return to Earth later this decade.
“Until then, we are left with the possibility that, on our journey through space, we will be accompanied by the debris of a collision that left a hole in the Moon,” said Byrne. “And that’s really cool.”
Translated by Luiz Roberto M. Gonçalves.
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