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Late day at the Uppsala Schmidt Telescope at Siding Spring Observatory,
New South Wales, Australia. The telescope is used for the Siding Spring
Survey, the southern hemisphere counterpart to UA's Catalina Sky
Survey. Both projects search for Earth-approaching asteroids. (Photo:
Courtesy of Steve Larson, Catalina Sky Survey)
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Astronomers Take Search for Earth-Threatening Space Rocks To Southern Skies
By Lori Stiles
April 06, 2004
The hunt for space rocks on a collision course with Earth has so far been pretty much limited to the Northern Hemisphere.
But last week astronomers took the search for Earth-threatening asteroids to southern skies.
Astronomers using a refurbished telescope at the Australian National
University's Siding Spring Observatory discovered their first two
near-Earth asteroids (NEAs) on March 29. NEAs are asteroids that pass
near the Earth and may pose a threat of collision.
Siding Spring Survey (SSS) astronomer Gordon Garradd detected a roughly
100-meter (about 300-foot) diameter asteroid and 300-meter (about
1,000-foot) diameter asteroid in images he obtained with the 0.5-meter
(20-inch) Uppsala Schmidt telescope.
SSS partner Robert H. McNaught confirmed both discoveries in images he
took with the Siding Spring 1-meter (40-inch) that same night.
The 100-meter asteroid, designated 2004 FH29, makes a complete orbit
around the sun every 2.13 years. It missed Earth by 3 million
kilometers (1.9 million miles), or 8 times the Earth-to-moon distance,
yesterday, traveling at 10 km per second (22,000 mph) relative to
Earth.
The 300-meter asteroid, designated 2004 FJ29, orbits the sun about
every 46 weeks. It came within 20 million kilometers (12 million
miles), or within 52 lunar distances of Earth, last Tuesday, March 30,
traveling at 18 km per second (40,000 mph) relative to Earth.
Neither object poses a direct threat of colliding with Earth.
Had the asteroids not missed, damage from their impacts would have
depended on what kind of rock they're made of. The 100-meter object
likely would mostly burn up in Earth's atmosphere in an airblast
equivalent to 10 megatons of TNT, comparable to the 1908 explosion
above the Tunguska River valley in Siberia, McNaught said. The
300-meter rocky asteroid likely would reach Earth's surface, dumping
the equivalent of 1,400 megatons of TNT energy into Earth's atmosphere,
he added. That's comparable to 200 Tunguskas, or 24 times the largest
thermonuclear bomb explosion, a 58 megaton Soviet bomb exploded in
1961.
The new survey is a joint collaboration between the University of
Arizona Lunar and Planetary Laboratory and ANU's Research School of
Astronomy and Astrophysics. It is funded by NASA's Near-Earth Object
Observation Program, a 10-year effort to discover and track at least 90
percent of the one kilometer (six-tenths of a mile) or larger NEOs with
the potential to become impact hazards. 
The 0.5-meter (20-inch) Uppsala Schmidt Telescope, Siding Spring Observatory. |
When astronomers detect what they suspect is an NEA, they immediately
must take additional images to confirm their discovery, McNaught said.
Surveys often have to suspend their NEA searches and spend observing
time confirming NEAs, or they risk losing them altogether because
follow-up observations were made too late, he added.
The SSS plan is to use the 1-meter (40-inch) telescope for part of the
month to quickly confirm suspect asteroids detected with the Uppsala,
freeing the smaller telescope to continue it searches.
"Our confirmation strategy worked beautifully on our first try," McNaught said.
The Uppsala Schmidt telescope was built in the 1950s for Uppsala
Observatory in Sweden. It was sited at Stromlo as the Uppsala Southern
Station to make wide field photographs of the southern sky. Increasing
light pollution from Canberra led to its relocation to Siding Spring,
near Coonabarabran in New South Wales, in 1982. Despite its high
quality optics, the telescope drifted into disuse because it used
photographic film rather than modern electronic detectors and had to be
operated manually.
In 1999, McNaught and Stephen M. Larson of UA’s Lunar and Planetary
Laboratory joined in an effort to refurbish and upgrade the Uppsala
telescope. Larson had similarly just overhauled a manually operated,
photographic wide-field Schmidt telescope in the Santa Catalina
Mountains north of Tucson for his Catalina Sky Survey (CSS), part of
the NASA-funded program to spot and track asteroids headed toward Earth.
The SSS builds on telescope control, detector technology and software
developed for the CSS in Tucson. During the upgrade, the Uppsala was
completely reconditioned, and fitted with computer control, a large
format (16 megapixel) solid state detector array, and extensive support
computers and software that detects objects moving against background
stars.
Larson said his reaction to the SSS milestone was "one of relief, since
it took several years to make the telescope and facility modifications.
Now the real work begins."
Larson and Catalina Sky Survey team member Ed Beshore worked on
commissioning the Uppsala telescope during the past few months.
Commissioning a telescope is like commissioning a ship: You have to get
all the parts working and working together, and adjust things so they
perform as expected.
"We actually achieved 'first light' last summer, with good images from the start," Larson said.
McNaught and Garradd will operate SSS about 20 nights each month. They
suspend operations when the week around full moon brightens the sky,
making faint object detection difficult.
The Catalina telescope, which Larson and his team upgraded again in May
2000, features new optics that give it a 69 centimeter (27-inch)
aperture and a new, more sensitive camera. In addition to Larson and
Beshore, Eric Christensen, Rik Hill, David McLean, and Serena Howard
operate CSS.
Both CSS and SSS telescopes can detect objects as faint as 20th
magnitude, close to sky background level generated by scattered city
light and auroral glow that brightens Earth’s upper atmosphere.
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