NASA's WISE satellite spots "horseshoe" asteroid

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    Unlike most near-Earth asteroids³ (NEAs) that have eccentric, or egg-shaped, orbits that take the asteroids（小行星） right through the inner solar system, the new object has an orbit that is almost circular such that it cannot come close to any other planet in the solar system except Earth, JPL said.

    However, even though the asteroid rides around with Earth, it never gets that close, said JPL in Pasadena, Los Angeles.

    As the asteroid approaches Earth, the planet's gravity causes the object to shift back into a larger orbit that takes longer to go around the sun than Earth. Alternately, as Earth catches up with the asteroid, the planet's gravity causes it to fall into a closer orbit that takes less time to go around the sun than Earth, according to JPL.

    The asteroid therefore never completely passes our planet. This slingshot-like effect results in a horseshoe-shaped path as seen from Earth, in which the new object, designated 2010 SO16, takes 175 years to get from one end of the horseshoe to the other, JPL said.

    "The origins of this object could prove to be very interesting, " said Amy Mainzer of JPL, the principal investigator⁴ of NEOWISE, which is the asteroid- and comet-hunting portion of the WISE survey mission. "We are really excited that the astronomy community is already finding treasures in the NEOWISE data that have been released so far."JPL manages and operates the WISE for NASA's Science Mission Directorate, Washington.(本文由在线英语听力室整理编辑)

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