Is it a new asteroid mini–moon or a human-made mini-moon? That’s the question about a small object approaching Earth, called 2020 SO. NASA’s Small Body Database predicts the object will captured by Earth’s gravity in October 2020 and temporarily be trapped in orbit.

But a few unusual characteristics of 2020 SO suggest it might not be a small asteroid, like the two previously known temporary mini-moons that have briefly orbited our planet. Instead, this new object might in fact be an old object from Earth—an old second-stage rocket part from the Surveyor 2 lunar lander mission, launched in 1966.

Mini-moons, or TCOs (Temporarily Captured Objects) have probably occurred more over history than we know, but only two have ever been confirmed: 2006 RH120, which hung out in Earth orbit from 2006 to 2007, and the one discovered earlier this year, 2020 CD3, in Earth orbit from 2018 to 2020. Those objects were definitely small space rocks.