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01101001
2008-Feb-14, 04:50 AM
Planetary Society Weblog: Triple near-Earth asteroid discovered (http://www.planetary.org/blog/article/00001326/)


Astronomers using the soon-to-be-closed(?) Arecibo observatory announced today the discovery of the first near-Earth object known to be a triple system. Asteroid 153591 (2001 SN263) was first discovered as a mote of light by the LINEAR project on September 19, 2001. Asteroid 153591 (2001 SN263) is now on a relatively close pass by Earth; it'll approach within 10 million kilometers on February 20. [...] Arecibo is routinely used to study the shapes and sizes of near-Earth asteroids on close approaches to Earth, and Arecibo radar images of such asteroids have yielded the discoveries of numerous binaries among the near-Earth asteroid population. But this is the first time it's turned up a triple system. The three bodies are 2, 1, and 0.4 kilometers across -- really quite remarkably similar in size. It's hard for me to imagine how such a system would be stable, unless one of the components orbits the others at quite a great distance.

hhEb09'1
2008-Feb-14, 05:50 AM
Just what are we looking at in that "image from the Arecibo radio telescope" at that webpage (http://www.planetary.org/blog/article/00001326/)? Is that large object with the round edge one of them, but all three are supposedly about the same size?

Neverfly
2008-Feb-14, 07:32 AM
Just wait 'til TU24.org hears of this one.

Triple Polarity with E.U. disturbances;)

01101001
2008-Feb-14, 04:38 PM
Cornell University: Arecibo Observatory astronomers discover first near-Earth triple asteroid just 7 million miles away (http://www.news.cornell.edu/stories/Feb08/AreciboAsteroid.html)

They repeat the image (courtesy Arecibo Observatory):

http://www.news.cornell.edu/stories/Feb08/asteroid.png (http://www.news.cornell.edu/stories/Feb08/AreciboAsteroid.html)


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 across, or about the size of the Arecibo telescope.

Ah, there's a NAIC images page (http://www.naic.edu/~pradar/asteroids/2001SN263/).

Another radar view:

http://www.naic.edu/~pradar/asteroids/2001SN263/SN263.feb12.s.gif (http://www.naic.edu/~pradar/asteroids/2001SN263/)


Just what are we looking at [...]? Is that large object with the round edge one of them, but all three are supposedly about the same size?

The "narrower" smaller objects are explained.


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 one-inch resolution.