When is an orbit not an orbit?

When it is the orbit of a weird asteroid.

A newfound asteroid has been discovered to be trailing Earth on an oddball course: an orbit that looks a lot like a horseshoe.

The space rock, called asteroid 2010 SO16, has been following Earth as our planet orbits the sun for at least 250,000 years and is up to 1,312 feet (400 meters) wide, scientists said. It was initially spotted by NASA's WISE infrared space observatory.

"Its average distance from the sun is identical to that of the Earth, but what really impressed me at the time was how Earth-like its orbit was," said Apostolos Christou, an astronomer at the Armagh Observatory in the United Kingdom, who led the study that pinned down the asteroid's orbit.

...

Currently, the asteroid is at a point in its orbit that brings it near the horseshoe's tip that trails the Earth. But despite its apparent attachment to Earth's orbit, the asteroid poses no risk of smacking our planet.

"This asteroid is terraphobic," Christou said. "It keeps well away from the Earth. So well, in fact, that it has likely been in this orbit for several hundred thousand years, never coming closer to our planet than 50 times the distance to the moon."

...

Asteroid 2010 SO16 is not the only space rock known to circle the sun in a horseshoe pattern that brings it near Earth. At least three other asteroids are known to have similar orbits, though not as stable as that of 2010 SO16, researchers said. Those other asteroids will linger in Earth's neighborhood for a few thousand years before moving on, they added.

(from Space.com)





Horseshoe pattern? Looks more like a "C" to me.