(Newsweek) – A mysterious object will fly past the Earth tomorrow and scientists still aren’t quite sure what it is. The object, dubbed 2020 SO by astronomers, will come within “just” 31,605 miles of our planet at 3:50 a.m. ET on December 1, according to NASA’s Center for Near-Earth Object Studies (CNEOS.)

This is an “extremely close,” albeit safe, approach, with the object passing at a distance equivalent to around 13 percent of the average distance between our planet and the moon, astronomer Gianluca Masi from the Virtual Telescope Project told Newsweek.

The object, which is estimated to measure between 15-33 feet across, was discovered by the Pan-STARRS survey based in Maui, Hawaii, on September 17, 2020. This find was confirmed two days later by the Minor Planet Center, which is responsible for the designation of minor bodies in the solar system. Initial observations suggested that the object was an asteroid. But scientists at CNEOS soon began to suspect that 2020 SO was not a normal asteroid.

“We are not sure it is an asteroid—that is, a natural body,” Masi wrote on the Virtual Telescope Project website. CNEOS director Paul Chodas subsequently suggested that 2020 SO may not be an asteroid at all, tentatively identifying it as the Centaur rocket booster from NASA’s failed Surveyor 2 lunar mission, which launched on September 20, 1966. READ MORE