Mystery solved: NASA confirmed the space object that just zipped past Earth is a 1960s rocket booster

• NASA has confirmed that a mysterious object that just flew past Earth is the dead booster of a 1960s Centaur rocket.
• Earth's gravity briefly captured the booster this year, causing it to loop the planet twice before returning to an orbit around the sun.
• Scientists confirmed that the object was a Centaur booster by comparing its electromagnetic fingerprint to that of a known Centaur booster in space.

A mysterious object zipped past Earth on Tuesday, coming within 32,000 miles of our planet. After months of head-scratching, scientists finally identified this visitor from beyond.

It's not an asteroid. It's not a comet. It's not an alien spaceship. On Wednesday, NASA confirmed that the object, formerly known as 2020 SO, is the booster of a Centaur rocket that launched in 1966.

The rocket carried the Surveyor 2 mission, which was set to land on the moon, but went into a death spiral when one of its thrusters failed to fire with the others. Surveyor 2 crashed into the lunar surface, but the rocket booster had separated from the spacecraft shortly after pushing it towards its lunar destination. The booster then drifted, unseen, into the abyss of space.

Now Earth's gravity has briefly captured the rocket booster once again, like a tiny moon orbiting our planet. It's set to loop Earth twice before escaping the planet's pull in March 2021. Then it will continue on a new orbit around the sun.

Its Tuesday flyby was the dead booster's closest approach to our planet.

A telescope on the Hawaiian island Maui first spotted the new space object in September. Its orbit seemed unnatural, following unusually close to Earth and remaining within the same plane as our planet. Most asteroids have tilted orbits, dipping above or below Earth as they journey around the sun.

"I was suspicious immediately," Paul Chodas, director of NASA's Center for Near-Earth Object Studies (CNEOS), told the New York Times.

Like Chodas, many scientists had suspected that this object was the Surveyor 2 booster, since reverse simulations of its orbit placed it so close to Earth in September 1966 that it could have easily come from our planet.

To test the theory, scientists used a NASA telescope on Hawaii's Maunakea to watch 2020 SO as it flew past Earth. They logged the object's spectrum data — wavelengths of electromagnetic radiation that act like fingerprints for objects in space. Different wavelengths represent different chemical compounds.

Scientists then compared the 2020 SO spectra to that of a known Centaur rocket booster, which has been orbiting Earth since it launched a satellite in 1971. The fingerprints matched.

"This conclusion was the result of a tremendous team effort," Vishnu Reddy, a planetary scientist at the University of Arizona who led the study, said in a press release. "We were finally able to solve this mystery."