3753 Cruithne It was not until 1997 that its unusual orbit was determined by Paul Wiegert and Kimmo Innanen, working at York University in Toronto, and Seppo Mikkola, working at the University of Turku in Finland. Cruithne is approximately in diameter, and its closest approach to Earth is , approximately thirty times the separation between Earth and the Moon. From 1994 through 2015, Cruithne made its annual closest approach to Earth every November. Although Cruithne's orbit is not thought to be stable over the long term, calculations by Wiegert and Innanen showed that it has probably been synchronized with Earth's orbit for
Near-Earth object February 15, 2013, the asteroid 367943 Duende () passed approximately above the surface of Earth, closer than satellites in geosynchronous orbit. The asteroid was not visible to the unaided eye. This was the first close passage of an object discovered during a previous passage, and was thus the first to be predicted well in advance. Some NEOs are of special interest because they can be physically explored with lower mission velocity than is necessary for even the Moon, due to their combination of low velocity with respect to Earth and weak gravity. They may present interesting scientific opportunities both for