Most near-Earth asteroids (NEAs) are egg-shaped, with eccentric orbits that move directly through the inner solar system. However a new object discovered by NASA’s WISE infrared telescope and named2010 SO16, is different: hisorbit is almost circular, so it cannot approach any other planet in the solar system except Earth.
However, althoughthe asteroid revolves around the Sun like Earth, it never gets so close as to be a threat. “It stays well away from Earth,” explains Apostolos Christou, who, together with David Asher of the Armagh Observatory in Northern Ireland, analyzed the body’s orbit after it was discovered in infrared images taken by WISE. “It has probably been in this orbit for several hundred thousand years, buthas never approached our planet at distances less than 50 times the distance to the Moon.”
This asteroid is one of the few thattrace a horseshoe shape with respect to Earth. As the asteroid approaches our planet, its gravity causes the object to shift back into a larger orbit that takes longer to revolve around the Sun than Earth. Alternatively, as Earth reaches the asteroid, the planet’s gravity causes it to fall into an orbit closer to our star, with less time to orbit the Sun than Earth. Therefore, the asteroid never completely exceeds our planet. East“slingshot effect” results in a horseshoe-shaped course, seen from Earth, in which2010 SO16 takes 175 years to get from one end of the horseshoe to the other.
