For about a month in 2002, J002E was discovered and thought to be an asteroid. It was found to be orbiting Earth, which was unusual because the only large object to do that is, well, the Moon.
Then NASA did some measurements and concluded that it was a man-made object. J002E3, it turned out, was the third stage of the Saturn V rocket from November 1969. The rocket helped launch Pete Conrad, Alan Bean, and Richard Gordon on the Moon landing mission of Apollo 12. When he reached the Moon’s surface, Conrad famously said: “Whoopie! Man, that may have been a small one for Neil, but that’s a long one for me.”
Read more about the history of J002E3 here.