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First near-Earth triple asteroid discovered

Date: 17-Feb-08
Author: Cornell University

Once considered just your average single asteroid, 2001 SN263 has now been revealed as the first near-Earth triple asteroid ever found. The asteroid -- with three bodies orbiting each other -- was discovered by astronomers at the sensitive radar telescope at Cornell University's Arecibo Observatory in Puerto Rico.

Cornell University and Arecibo astronomer Michael C. Nolan said he and his colleagues made the discovery when they obtained radar images Feb. 11.

The main, central body is spherical with a diameter of roughly 1.5 miles (2 kilometers), while the larger of the two moons is about half that size. The smallest object is about 1,000 feet (305 meters) across, or about the size of the Arecibo telescope.

Other triple asteroids exist in the asteroid belt (between Mars and Jupiter) and beyond, but this is the first near-Earth system where the actual shapes of objects can be clearly seen.

These radar images of near-Earth asteroid 2001 SN263 were obtained on 2008 Feb 12 and 13. The resolution is 75m (250 feet) per pixel. Because the moons are rotating more slowly than the larger "primary", they appear narrower to the radar, which measures distance and speed. Arecibo transmitted 500,000 Watts toward the asteroid, but the echo power received with Arecibo's ultra-sensitive detectors and processed into these images totals less than a billionth of a billionth of a billionth of a Watt. Arecibo is both the world's most powerful radar transmitter and the world's most sensitive radio receiver.

This experiment produced 75-meter-resolution images of a 2-km asteroid when it was about 11,000,000 km away. This is like using a camera in New York to image a person in Los Angeles with 2.5-cm (one-inch) resolution.

Courtesy: Michael Nolan, Arecibo Observatory

Full story: First near-Earth triple asteroid discovered by Arecibo Observatory astronomers