Mystery Object in Earth's Orbit
"A small asteroid-like object has been discovered in an orbit about the Sun
that is so similar to the Earth's orbit that scientists strongly suspect it to be
a rocket stage that escaped years ago from the Earth-Moon system. The
object was discovered on May 16, 2010 by Richard Kowalski at the Catalina
Sky Survey, and has subsequently been observed by many observers,
including Bill Ryan (Magdalena Ridge Observatory) and Peter Birtwhistle
(England). It was given the asteroid designation 2010 KQ by the Minor
Planet Center in Cambridge Massachusetts, who identified its orbit as
being very similar to that of the Earth."
NASA: Is Approaching Space Object Artificial?
(2010 KQ) - JPL Small-Body Database Browser