A newly discovered Near Earth Orbiting Asteroid (NEO) has turned out to have a most unusual orbit, that is best described as "horse-shoe" shaped!

Seen from the astereoids point of view it is orbiting the sun in a normal orbit though. But being so close top the orbit of the much heavier Earth, it's orbit changes for each close-encounter.

To understand this, first realise,taht objects closer to the sun will orbit at a faster rate than objects of a further distance from the Sun

When 2010SA16 are orbiting the Sun within the radius of the Earth orbit, it catches up with Earth. But when closest to Earth, it's gravity pulls the asteroid away from the Sun, leaving the asteroid into an orbit at a greater distance from the sun than Earth. The asteroids new orbital track will then be slower than that of Earth, making it appear to fall behind and look as though it is going in the opposite direction.

These kinds of exotic orbits has been predicted, but are not stable. The researchers have however, símulated and tracked its orbit back in time, and concludes taht it has been in this strange orbit somewhere between 120 000 and 1 million years!

Source: arXiv