From: University of Arizona
Posted: Wednesday, January 18, 2006
When it comes to finding asteroids or comets that swing too close to home, the Catalina Sky Survey is currently Earth's best defense.
The Catalina Sky Survey discovered more near-Earth objects (NEOs) than any other sky survey in 2005. That includes more NEOs larger than a kilometer in diameter, as well as more smaller objects that potentially threaten Earth.
The University of Arizona's NASA-funded Catalina Sky Survey (CSS) is directed by Stephen M. Larson of the Lunar and Planetary Laboratory. It is among a handful of surveys in NASA's 10-year, congressionally-mandated Spaceguard program that aims to discover at least 90 percent of the one-kilometer near-Earth asteroids and comets by the end of 2008. If an object even a third as large (300 meters) hit Earth, it would explode with 24 times the energy of the world's largest thermonuclear bomb explosion, a 58 megaton Soviet bomb exploded in 1961.
CSS astronomers discovered 310 NEOs, or 49 percent of all NEOs discovered in 2005. That's a record-breaking number of discoveries for any NEO survey, ever.
Of these, 29 objects are at least a kilometer across, and 40 are classified "potentially hazardous asteroids," objects large enough and close enough to Earth to bear watching. All other Spaceguard surveys found a total 46 potentially hazardous asteroids last year.
"I am elated," Larson said. He credits CSS's success to two developments. "We've finished upgrades on all three of our telescopes, so we have more sensitive detectors. And we've made a lot of improvements to our software so we can now process data much more efficiently."
Seven CSS astronomers operate two telescopes in the Santa Catalina Mountains north of Tucson, Ariz., and a third telescope, in collaboration with the Australian National University, at Siding Spring, Australia. That makes CSS the only NEO survey that covers both the northern and southern hemispheres.
During the past three years, CSS automated its three manually controlled telescopes, developed computer systems capable of processing large amounts of data and added three new, large format CCD cameras, all for about $500,000. Spectral Instruments of Tucson, Ariz., built the cameras, which incorporate ImagerLabs CCD chips thinned at the UA Steward Observatory Imaging Technology Lab headed by Mike Lesser.
The survey is a bargain for taxpayers, the astronomers noted. "We've done this survey on the cheap, relative to what other surveys expend," CSS astronomer Ed Beshore said.
CSS found nearly half the NEOs discovered in 2005 at just one-sixth the 2005 NASA Near-Earth Object Observations Program budget. The CSS team succeeded at finding about 25 NEOs a month despite a week of downtime due to lightning damage last year.
CSS shut down its original survey telescope near Mount Bigelow for a comprehensive upgrade and overhaul of virtually every telescope and detector subsystem in 2000. When the Schmidt telescope resumed routine observations in November 2003, it featured 0.7 meter (28 inch) optics, making it the second largest Schmidt-type telescope in the United States. The now-automated telescope has a wide-field camera (8 square degree field-of-view) that images large regions of sky, typically 1,000 square degrees of sky in a single night. At 8,250-feet, the Schmidt is higher than Tucson's air pollution. Pointing up and away from the city's lights, it can detect faint objects down to about 20th magnitude, or about 400,000 times fainter than visible with the naked eye.
Robert H. McNaught and Gordon Garradd of the Siding Spring Survey near Coonabarabran, New South Wales, began routine surveying in 2004. The Arizona and Australian team upgraded the 0.5 meter (20 inch) "Uppsala" Schmidt telescope with a camera and computer system identical to the CSS Schmidt in the northern hemisphere. The Australian astronomers also use a one-meter (40-inch) telescope to quickly confirm suspect asteroids detected with the Uppsala telescope.
At the same time, CSS upgraded and began using the UA's 1.5 meter (60 inch) Cassegrain reflector telescope at Steward Observatory's 9,100-foot Mount Lemmon site in December 2004. Its narrower (1.3 square degree) field-of-view camera images only a sixth the area that the Catalina Schmidt telescope covers, but it detects fainter objects than the Schmidt telescope does. The Mount Lemmon telescope can detect objects more than two million times fainter than visible with the naked eye.
CSS surveys a region of sky four times over 40 minutes to spot any close, fast-moving objects among the fixed background of more distant stars. "We observe a region more often than some other surveys because it helps us cut down spurious objects that show up and might be misinterpreted as being real," Larson said.
"Another advantage is that we're set up to do our own follow-up during the night," Larson added. "We're as close to a real-time system as you can get. We actually see results within an hour after they are taken, and then our software analyzes the data to see if an object moves like an NEO. If so, we get additional observations that same evening."
The survey requires six high-speed computers running simultaneously to process the 600 images, or 20 gigabytes of data, taken by each of the telescopes on a good observing night. That much data would fill nearly 30 CDs.
Survey astronomers report their NEO discoveries to the Minor Planet Center at Harvard University, which posts them to a Website called the NEO Confirmation Page. Amateur astronomers play a critical role by locating and further tracking the objects, CSS astronomer Ed Beshore said. Amateur astronomers provide needed followup observations to help refine an object's orbit, allowing the Minor Planet Center to confirm if objects are true NEOs or not.
Once an object is designated an NEO, the job isn't finished, however.
"If you don't continue to observe these things, the uncertainties in their orbits increase with time," Beshore said. "You have to re-observe them to make sure they're where you expect them to be. It's kind of a waste of taxpayers' money to observe them and then lose them. In addition to surveying, CSS plans to do a lot of recovery work to make sure that objects, once found, aren't lost again. Discovery and followup is sort of our good-citizen contribution to our planet's well-being."
CSS astronomers are merciless when it comes to squeezing incremental improvements from the telescopes and computer software, Beshore added. "We constantly talk about how to get another 5 percent from the telescope, how to cover more sky, how to observe fainter objects, how much more sensitive we can make the software, how we can make the software compensate for all the false detections we get by making it more sensitive. If you just ruthlessly attack the problem like that, pretty soon you've got 50 percent more efficiency in your system."
Continued efforts to improve CSS should pay off in an even better NEO yield in 2006.
The four other major NASA-funded NEO surveys include the MIT Lincoln Labs-Air Force LINEAR project at Soccorro, N.M.; UA's Spacewatch -- the pioneering NEO survey founded by Tom Gehrels and directed by Robert McMillan; Lowell Observatory's LONEOS at Flagstaff; and the Jet Propulsion Laboratory's NEAT program.
Last year, LINEAR discovered 137 NEOS, of which 22 were at least a kilometer in diameter and 20 were classified as potentially hazardous asteroids. Spacewatch discovered 82 NEOs, of which 10 were at least a kilometer in diameter and 8 were classified as potentially hazardous. The same numbers for LONEOS were 42 NEOs, 4 at a kilometer or larger and 10 potentially hazardous; and for NEAT were 38 NEOs, 9 at a kilometer or larger and 8 potentially hazardous.
Stephen M. Larson 520-621-4973 firstname.lastname@example.org
Ed Beshore 520-621-4900 email@example.com
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