2003 YN₁₀₇

2003 YN₁₀₇ (also written 2003 YN107) is a very small Near-Earth object. It was discovered by the Lincoln Near Earth Asteroid Research (LINEAR) system in orbit around the Sun on December 20, 2003. Its diameter is approximately 10 to 30 metres, which is near the most commonly used 10-metre demarcation line between meteoroids and asteroids. 2003 YN₁₀₇ is on NASA's Earth Close Approach list, and is estimated to miss the Earth by 0.0599 AU.

It revolves around the Sun on an Earth-like, almost circular, orbit. Its orbital period of 363.846 days also is very close to the Sidereal year. Its most remarkable properties are that it has kept a distance of less than 0.1 AU (15 Gm or 15 million kilometres) in the time from 1996 to 2006 and that it slowly orbits the Earth during one year. However, 2003 YN₁₀₇ is no second moon, as it is not bound to the Earth. It is the first discovered member of a postulated group of coorbital objects, or quasi-satellites, which show these path characteristics. Other members of this group include 10563 Izhdubar, 54509 YORP, (66063) 1998 RO₁, (85770) 1998 UP₁, and (85990) 1999 JV₆.

Before 1996, the asteroid had been on a so-called horseshoe orbit around the sun, along the Earth's orbit. After 2006, it had regained such an orbit. In that, it is very similar to the object 2002 AA₂₉. Apparently, this kind of orbit change is common for coorbital objects. 2002 AA₂₉ will become a quasi-satellite of the Earth in approximately 600 years.