(NEXSTAR) — An object of uncertain origin is expected to hurtle safely past our planet Tuesday, but the object is not a true UFO. Astronomers have been tracking the visitor, known as 2020 SO, since September when it was spotted from an observation station in Hawaii.

Originally thought to be an asteroid, NASA scientists have since suggested that it’s a piece of space junk left over from early U.S. space exploration.

“The object is likely not an asteroid,” NASA officials wrote in a November 12th research update. “It’s probably the Centaur upper stage rocket booster that helped lift NASA’s ill-fated Surveyor 2 spacecraft toward the Moon in 1966.”

NASA officials say the 2020 SO’s orbit did not look like a typical asteroid and much more closely resembled something originating from Earth. Computer modeling helped their team trace the likely origin to the 1966 launch.

“Shortly after lift-off, Surveyor 2 separated from its Centaur upper-stage booster as intended. But control of the spacecraft was lost a day later when one of its thrusters failed to ignite, throwing it into a spin. The spacecraft crashed into the Moon just southeast of Copernicus crater on Sept. 23, 1966,” NASA wrote of the mission. “The spent Centaur upper-stage rocket, meanwhile, sailed past the Moon and disappeared into an unknown orbit about the Sun.”

Researchers say it’s likely the object has passed through the Earth’s orbit in the past. This relatively close flyby Tuesday – at the proximity of about one-seventh the typical distance to the moon – should give skywatchers a close enough look to further confirm or disprove the rocket theory.

The object is believed to be in the range of 15 to 30 feet wide, according to NASA’s Jet Propulsion Laboratory. It should fly by harmlessly in the early hours of Tuesday morning.