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The Daily Need

Faraway, so close: the Earth’s most loyal stalker

Astronomers at the Armagh Observatory in Northern Ireland believe that an asteroid that’s been trailing the Earth for a quarter of a million years may share some of our planet’s DNA.

In a paper published in the Monthly Notices of the Royal Astronomical Society, Apostolos Christou and David Asher reveal the unusual orbit of 2010 SO16, an asteroid discovered in 2009 by the WISE satellite. 2010 SO16 orbits the sun at about the same distance as the Earth, almost sharing our planet’s orbit. But when it reaches the Earth, it does an abrupt about-face and goes back around the sun in the opposite direction, moving in a horseshoe pattern.

Source: Armagh Observatory

On the Observatory’s website, Christou described the asteroid as “terraphobic”: “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.”

The asteroid takes 175 years to move from one end of the horseshoe to the other, and is currently at one of the ends, trailing closely behind the earth.

At least three other known asteroids have a horseshoe-shaped orbital, but these are much younger and much smaller than 2010 SO16, and are expected to soon move off through the solar system to other orbits. 2010 SO16, however, has been in the same orbit for at least the last 250,000 years.

Christou and Asher are hoping to learn more about the asteroid while it is still nearby. They postulate that it may be leftover material from the formation of the Earth, moon and other inner planets 4.5 billion years ago. Continued study could reveal some clues about our own planet’s past.

Meanwhile, those wanting to get a glimpse of 2010 SO16 only need a medium-sized professional telescope to spot it. The astronomers say that the asteroid will remain as visible in the evening skies for years to come.

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