The near-Earth asteroid that could be a child of the Moon

Illustration of the asteroid Kamo`oalewa in the Earth-Moon system.

Illustration of the asteroid Kamo`oalewa in the Earth-Moon system.

The asteroid (469219) 2016 HO3 is an object close to the earth (NEO, for its acronym in English) that was discovered in 2016 with the PanSTARRS telescope from Hawaii (USA) and baptized as Kamo`oalewa in allusion to a baby or offspring of which a Hawaiian song of creation speaks. In fact, it could be so, and his ‘mother’, the Moon.

A team of astronomers led from the University of Arizona (USA) published this week in the journal ‘Nature Communications Earth and Environment’ a study which suggests that this small asteroid, of between 40 and 60 m in diameter, it is probably a fragment of our satellite: a small miniature moon that closely accompanies (about 14.5 million km) our planet.

Kamo`oalewa is a quasi-satellite, objects of which little is known due to their low brightness and being difficult to observe.. In this case it is about 4 million times fainter than the dimmest star that the human eye can capture in a dark sky, and due to its orbit and when illuminated by the Sun it can only be seen from Earth for a few weeks each month. of April.

The spectrum or pattern of reflected light from the asteroid Kamo`oalewa matches that of the lunar rocks brought back by the Apollo missions, suggesting that it comes from our satellite.

Using the Large Binocular Telescope (LBT) from Mount Graham, in southern Arizona, the team of astronomers led by graduate student Ben Sharkey and his tutor Vishnu Reddy discovered last April – in 2020 they could not because of the pandemic – that the spectrum or pattern of reflected light of this small asteroid coincides with that of the lunar rocks of the Apollo missions of the POT, which suggests that it came from our satellite.

“Kamo`oalewa reflects sunlight in a way that is more typical of the minerals found on the Moon (silicates) than of the more common asteroids,” Sharley explains to SINC, although he acknowledges that “more observations with telescopes would contribute new pieces to this puzzle, and the rsample collection of this object would directly confirm or reject this hypothesis ”. Scientists from the United States and China are already planning that possibility by sending missions.

The orbit of Kamo`oalewa also offers another clue to its lunar origin, since it is similar to that of our planet but with a slight inclination. It is not the typical one for near-Earth asteroids, underlines another of the authors, Renu Malhotra: “It is highly unlikely that a most common asteroid will spontaneously move into a near-satellite orbit like Kamo’oalewa’s. We estimate that it reached it about 500 years ago, and it will not stay here long, only about 300 years. ”

The article discusses the different possibilities about its origin. “One of them is that Kamo`oalewa is a common asteroid that has docked in its current orbit by sheer luck”, points out Sharkey, “but if its orbit is not a simple coincidence, that tells us that could be related to the Earth-Moon system. And if it comes from the Moon, we might think that it has received many impacts throughout its history. Perhaps this asteroid is the result of one of them. ”

In any case, the authors are not sure how it could have detached, in part because other asteroids of lunar origin are not known.

Ejection of material by impacts on the Moon

The astronomer Carlos de la Fuente Marcos from the Complutense University of Madrid, who has not participated in the study, recalls that there are calculations on the evolution of the ejected material during the formation of impact craters in Moon, that a few meteorites are known whose lunar origin is 100% confirmed thanks to the samples of the Apollo program and some of the Russians, and that the impacts on our satellite continue to occur today.

Material of lunar origin is being inserted into space near Earth: one part may collide with our planet producing meteorites and the rest remain in an asteroid belt

“Therefore,” he points out, “the scientific community is clear that material of lunar origin is being inserted into space near the Earth: a fraction can collide with our planet producing meteorites and the rest can remain in the circumterrestrial region forming part of the asteroid belt of the Arjunas, objects that share the orbit of our planet. But until now no solid evidence has been found, such as that of Kamoʻoalewa, for the existence of near-Earth asteroids that could have their origin in relatively recent lunar impacts ”.

“Most of the Arjuna-type asteroids have not been studied spectroscopically and it would not be strange if there were more with spectra compatible with the composition of the lunar material brought by the Apollo missions,” predicts De la Fuente Marcos, co-author of studies where other Earth’s quasi-satellites, such as 2020 PP1, who appear to be dynamic relatives of Kamo’oalewa.

“It would not surprise us if some of these objects had a spectrum consistent with that of Kamo’oalewa – he concludes – but unfortunately they are extremely difficult to observe and only the largest telescopes (such as the LBT or the Gran Telescopio CANARIAS) can provide us with spectroscopic information. from them”.


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