A satellite image shows the far side of the moon as it crosses between the DSCOVR spacecraft and the Earth.


We’ve all been taught from a very young age that the Earth has just one natural satellite. The moon is there, it’s easy to see at night from just about anywhere and for the most part, it’s a pretty neat little friend for our planet. Some other planets in our solar system have lots and lots of moons, but we only have one … right?

A new study proposes that the moon is actually just the biggest of Earth’s satellites and that other “mini-moons” orbit our planet, but are so tiny, and come and go so often, that we hardly ever notice them.

The research, which was published in Frontiers in Astronomy and Space Sciences, was conducted by an international team of astronomers who now say that tiny objects in space regularly swoop into orbit around Earth. They’re small, only between 1 and 2 meters in diameter, but they do show up from time to time and they could offer scientists a window into the life cycle of asteroids.

Modal TriggerImage of the moon
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As the researchers explain, the first of these “mini-moons” was detected in 2006. It was the first time any natural object had been observed orbiting Earth, aside from the moon itself, and it was clear that the rock was a rogue object that had simply been captured by Earth’s gravity, but it was still a significant finding.

Scientists call these objects “temporarily captured orbiters” (TCOs) and “temporarily captured flybys” (TCFs). As the names imply, these natural bodies don’t remain in orbit around Earth for very long, but instead slingshot themselves back out into space soon after making their appearance in the sky. TCOs complete at least one full orbit, while TCFs sometimes just graze Earth before flying away at high speeds.

To date, just one TCO has been observed — the aforementioned mini-moon spotted in 2006 — but the researchers believe that new telescope technology will allow us to spot more and more of these objects on a regular basis. If that happens, astronomers can begin to study them in more detail and potentially use them as models for the movement of asteroids around our solar system.