Discovered in 2002 by an amateur astronomer, J002E3 was initially believed to be an asteroid passing through space. However, scientists were able to determine that the object was covered in white titanium dioxide paint, identical to that used on NASA rockets.
After determining that it was white titanium paint, astronomers concluded that J002E3 is, in fact, the third-stage S-IVB rocket of the Apollo 12 mission. J002E3 returned to a highly elliptical orbit around the Earth after being in space for 30 years.

Source: How a Long-Gone Apollo Rocket Returned to Earth – Astronomy Magazine

PC: Wikipedia