 | | Catalina
Sky Survey director Stephen M. Larson (right) and David Brooks of
Seattle, Wa., discuss the 60-inch telescope at Steward Observatory's
Mount Lemmon site. The telescope can detect objects two million times
dimmer than the human eye can see. (Photo: Lori Stiles, University
Communications) |
Catalina Sky Survey Tops 2005 NEO Discoveries By Lori Stiles
January 17, 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. 
Larson
(left) and Eric Christensen of the Catalina Sky Survey search for NEOs
from the control room at the 60-inch Mount Lemmon telescope. |
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
28-inch CSS Schmidt telescope, the upgraded version of the original CSS
Schmidt telescope. It is the second-largest Schmidt telescope in the
United States. |
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. 
The Siding Spring Observatory in New South Wales, Australia, expands Catalina Sky Survey coverage over the southern hemisphere. |
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.
 
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