Image credit: Michael Nolan, Arecibo Observatory. 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.
Selections from the article (note there is also an associated press release on Arecibo's discovery of a triple asteroid 2001 SN263, the first one of its kind found)...
Nolan [Michael Nolan, research associate and head of radar astronomy at Arecibo] said Arecibo’s budget is now $12.5 million per year, but it will be cut 10 percent in 2009, and 40 percent by 2011.
Rep. Dana Rohrabacher, R-Cal., a member of the House Committee on Science and Technology, has co-sponsored a bill in a bi-partisan effort to appeal to NASA and the NSF to keep Arecibo running. He is sponsoring the bill with Luis Fortuna, resident commissioner of Puerto Rico, a nonvoting member of the House of Representatives.
Tara Setmayer, communications director for Rohrabacher, said the bill will ask for the NSF to fully fund Arecibo, allowing scientists to continue their work in radio astronomy and solar system research. It does not specify exactly how much funding should be set aside.
The bill also calls for cooperation between NASA and the NSF.
Nolan said the Arecibo telescope gathers data rather than taking pictures of the asteroid. He said scientists bounce radio waves off the asteroid and then use the data they obtain to find out the rock’s mass, density, orbit and other features.
“You send out a narrow pulse and first it bounces off the front of the asteroid,” he said. “And then a few microseconds later it bounces off a piece farther away, and so we can sort of patch that back together and make these images.”
Cornell research associate Ellen Howell said as the asteroid spins, astronomers make a two-dimensional image of it on their computers.
Howell said Arecibo’s capabilities are unique, because it can react quickly to new discoveries by approving urgent proposals for additional observation.
“Sometimes in as little as three or four hours, we can change the schedule, get all the right people assembled and get the telescope going,” Howell said.
Howell said she and her colleagues had been planning to look at the near-Earth asteroid, known as 2001 SN263, for a while. She and other astronomers thought it was simply a large rock and did not realize it has two moons.
“We didn’t know there was anything special about it until we got the first images,” she said.
Nolan said the main rock in the asteroid’s system is 2.7 km in diameter, or about 1.5 miles. Howell said the largest moon is half that size, and the smaller moon is 1000 m in diameter.
Howell said the triple asteroid is the closest one to Earth astronomers have ever found, though they have seen binary asteroids, with only one moon, close to Earth before.
The discovery raises many questions for Howell and her fellow astronomers, such as whether this triple system is stable and whether it formed as a three-part asteroid or picked up the third rock later.
Setmayer said Rohrabacher believes maintaining Arecibo is vital to national security, since its use of radar makes it uniquely suited for finding potentially dangerous near-Earth objects.
"Cornell telescope lacks funding despite rare asteroid discovery"
Clara Eisinger
The Ithacan
06 March 2008
Link: Article
Link: Cornell University Press Release on Triple Asteroid Discovery (13 Feb. 2008)
link: Arecibo Images and New Release
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