Earth Has A Companion Asteroid With a Weird Orbit

by NANCY ATKINSON on APRIL 6, 2011

In this graphic of a horseshoe orbit from NASA, Horseshoe orbits follow contour lines that enclose Lagrange points L3, L4 & L5. Credit: NASA

There are plenty of near-Earth asteroids out there, but this latest one studied by two researchers at Armagh Observatory in Northern Ireland is extremely rare in that it has a weird, horseshoe-shaped orbit. Not that Asteroid 2010 SO16 does an about-face and turns around in mid-orbit — no, the asteroid always orbits the Sun in the same direction. But because of its unique orbital path and the gravitational effects from both the Earth and the Sun, it goes through a cycle of catching up with the Earth and falling behind, so that from our perspective here on Earth, its movement relative to both the Sun and the Earth traces a shape like the outline of a horseshoe: it appears to approach, then shift orbit, and go farther away without ever passing Earth.

This asteroid was discovered on September 17, 2010 by the WISE Earth-orbiting observatory.