For now, only one such ‘minimoon’ has been detected, but astronomers are convinced there could be many more lurking in Earth’s orbit.

While you might think that the moon is our only natural satellite, this is certainly not the case, reveals an exciting study published earlier this year in the journal Frontiers in Astronomy and Space Sciences. One other object has been found zipping around our planet — “Earth’s first known natural geocentric object other than the moon,” the study authors point out.

Spotted in 2006 by the Catalina Sky Survey in Arizona, this intriguing object is a small asteroid only a few meters wide and is described by the researchers as a temporarily-captured orbiter (TCO), also known as a minimoon.

Dubbed RH120, this is the only Earth minimoon found to date. But the scientists — an international team from several U.S. universities and three European countries, Finland, Sweden, and Spain — believe there could be many more just like it in Earth’s orbit, waiting to be discovered.

According to the team, the main reason why we haven’t detected them yet is because they’re extremely small. In fact, astronomers expect our planet is orbited by an entire host of minimoons no wider than 1 to 2 meters (3.2 to 6.5 feet) — “with the number of captured meteoroids increasing exponentially for smaller sizes,” reads the study.

And, as it turns out, this “steady population” of minimoons around our planet could prove to be a real asset by helping us understand more about the Earth-moon system, as well as about asteroids in general.

In fact, the team advocates that we send spacecraft to study the TCOs circling our planet and even grab samples to find out what they’re made of, reports

“Minimoons can provide interesting science and technology testbeds in near-Earth space,” said study lead author Robert Jedicke, an astronomer at the University of Hawaii at Mānoa, Honolulu. “The challenge lies in finding these small objects, despite their close proximity.”

Our best chance of detecting these small objects trapped in our planet’s orbit is the Large Synoptic Survey Telescope (LSST), an 8.4-meter ground-based telescope currently being built in Chile which is expected to begin science operations in 2021.

“The LSST is the dream instrument for discovering tiny, fast-moving asteroids, and we expect it will regularly discover temporarily captured objects within the next five years,” said Jedicke.

Why are TCOs so fascinating? Well, for one thing, they break the solitude of the moon, proving our planet is frequently orbited by more than just one object. On top of that, these minimoons could further our understanding of small asteroids.

“We don’t know whether small asteroids are monolithic blocks of rock, fragile sand piles, or something in between,” said study co-author Mikael Granvik, affiliated with both the Luleå University of Technology in Sweden and the University of Helsinki in Finland.

Bu studying Earth’s minimoons we could finally get some answers in this respect, Granvik points out.

“Minimoons are perfect targets for bringing back significant chunks of asteroid material, shielded by a spacecraft, which could then be studied in detail back on Earth.”

In addition, future spacecraft missions to Earth’s TCOs could help us investigate how small asteroids form and evolve in the asteroid belt, as well as explore the dynamics of the Earth-moon system, the team details in the study.

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