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Earth's new minimoon might be a rocket humans launched into space in the 1960s

The Catalina Sky Survey spotted this object moving against the starry background before realizing it is an incoming minimoon.
The Catalina Sky Survey spotted this object moving against the starry background before realizing it was an incoming minimoon.
(Image: © Catalina Sky Survey)

Earth is getting a small new moon, but it might have been made by people.

Astronomers at the Catalina Sky Survey in Arizona first detected the object back in February as a flash of light darting across space.

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Right this moment, it's not in orbit around the Earth, but it's nearby. And it's going to enter Earth's orbit for a while in 2020 before heading out to circle the sun again.

The initial assumption was that this mysterious blip was an asteroid. The object, termed 2020 SO2 by the Jet Propulsion Laboratory, appears to have been temporarily captured by Earth's gravity. Earth has captured "minimoons" like this before, and scientists have spotted them a couple times in recent years. It's a natural part of our planet's movement through space.

But some observers now say this minimoon might not be natural after all. People built it, they think, back in the 1960s.

There's been some disagreement on this point, which played out on an astronomy message board known as the Minor Planet Mailing List (MPML), an online community frequented by professionals and hobbyists.

The issue is that 2020 SO2 is in an orbit around the sun that closely matches Earth's. Objects like that sometimes fall into Earth's gravity and end up orbiting for a little while. There are plenty of natural asteroids that behave this way, and there are even rocket parts that humans have  launched into space that have similar orbits.

By analyzing 2020 SO2's current movements and extrapolating them backward in time by using computer simulations, observers have worked out that this object would have last orbited Earth in 1966 or 1967. That could mean that 1966 or 1967 is when it was launched into orbit in the first place, or when 2020 SO2 naturally approached Earth.

But distinguishing the two possibilities is tricky. Initially, Sam Deen, an amateur astronomer in California, posted that no 1966 or 1967 launches match 2020 SO2's behavior, meaning that the curious object was likely natural. (Deen has been cited by NASA in the past.) Then Paul Chodas, director of NASA's Center for Near Earth Object Studies, told CNN that it was likely a rocket from Surveyor 2, an uncrewed NASA moon mission that launched on September 20, 1966. The object's orbit is so similar to Earth's, he said, that it probably came from Earth. Others on the MPML agree.

Another amateur astronomer, Tony Dunn, created a simulation of the object's path, which will take it very close to Earth in December and again in February.

It's possible that as 2020 SO2 comes closer, more detailed observations will  settle the matter. But in the meantime, we're left wondering whether Earth's incoming minimoon is a long-lost thing from this planet, or a space rock dropping in for a short visit

Originally published on Live Science.