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From Canadian Geographic

Space is relatively empty, but every once in a while...

DAVE BALAM was sitting alone in his office just before midnight on December 8, 1994, when an urgent message flashed across his computer screen. The cryptic dispatch from astronomer Jim Scotti in Tucson, Ariz., read, "Something's really moving out there." Balam, a 51-year-old astronomer who uses the Dominion Astrophysical Observatory in Victoria, knew that "something," in this case, meant an incoming asteroid. Scotti's accompanying data on the asteroid's trajectory indicated a "close encounter of the worst kind."

       The newly discovered asteroid -- coded 1994 XM1-had the mass of a large house and was moving at 108,000 kilometres an hour. Scotti figured it stood a good chance of striking Earth. Russia was a likely target; so was Canada. It would hit in 14 hours.

       Balam's mind raced. Should he call his mother? Would he hear the sonic boom? "I thought, All these years I've been waiting for an Earth impact to happen," says Balam, one of the world's leading experts on near-Earth objects (NEOs). "But if it missed, I didn't want to be Chicken Little, causing a panic."

       The fact is, says Balam, Chicken Little's right. The sky is falling. Although 1994 XM1 missed the Earth by 105,000 kilometres, the danger of NEOs is real. Since 1980, the half dozen members of the Spacewatch asteroid-detection team at the University of Arizona in Tucson have located more than 30,000 new asteroids and comets. Of those, 211 asteroids are NEOs.

       The roots of Balam's infatuation with comets and asteroids were planted at the age of six, when his father bought him a small telescope. By age 11, he had moved on to amateur telescope building and a fascination with the moon. Graduation to star clusters, galaxies and novas followed. At the time, there were about 1,600 permanently numbered asteroids in the solar system. Three came near Earth. Today the number of asteroid discoveries is increasing at a rate of tens of thousands a year. Most of these circle uneventfully between Mars and Jupiter. But those known to approach the Earth's orbit number more than 1,000; and those on the Potentially Hazardous Asteroids list number about 250.

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       In 1990, when American geophysicist Glen Penfield and Canadian planetary scientist Alan Hildebrand identified the Chicxulub Crater on Mexico's Yucatαn Peninsula coastline as the impact point of a 10- to 20-kilometre-wide object, scientists began reevaluating the role NEOs play in planetary evolution. Evidence suggests that about three quarters of the Earth's animal species -- including dinosaurs -- were wiped out in that cataclysm 65 million years ago. ASTRONOMY has gone through a revolution during the past decade. The old way of viewing and photographing images through telescopes has been largely replaced by a digital process far more sensitive than film. Together with advanced robotic tracking systems and modern computers, astronomers now have a sobering perspective on the hazards lurking in the Earth's vicinity. The goal of today's NEO researcher is to find Earth-bound rocks before they find us.

       No one knows more about this than Balam's colleague, Jim Scotti, who spends about six nights a month inside the huge Spacewatch telescope atop 2,063-metre Kitt Peak, southwest of Tucson. In late 1997 he sat in the telescope's control room, staring into his computer monitor and wondering what newly located 1997 XF11 might do. He knew it was a near-Earth asteroid by its motion. Some simple calculations suggested that in the year 2028, the two-kilometre-wide rock would approach precariously close to Earth. If it hit, millions could die from the impact or from the subsequent famine produced by a years-long, planet-wide winter. The chances of it hitting were a little better than witnessing a no-hitter, major-league baseball game -- unlikely, but not impossible.

       Scotti's computer screen displays a sequence of electronic celestial images gathered by the 90-centimetre telescope. When an object moves on the screen, a computer program notes it and Scotti begins analyzing its trajectory. So far on this night, he has found 36 new asteroids. When he identifies something new, Scotti e-mails its co-ordinates to the Minor Planet Centre of the International Astronomical Union in Cambridge, Mass., which distributes the data to follow-up teams around the world. Scotti also sends a copy to Balam.

       Balam, a research associate with the Department of Physics and Astronomy at the University of Victoria, sits alone in his observatory, his boyish face lit by the glow of his computer screen. He works through the night in a hunched frenzy of typing, blue eyes riveted on the electronic images of stars and galaxies and asteroids. With a tap of a key, a 1.8-metre telescope glides silently into position, and a series of images is taken of the target asteroid.

       Most asteroids are shattered remnants of the protosolar system, including rocks that never coalesced into planets 41Ž2 billion years ago. Others appear to be derived from debris blasted free of the moon or of Mars by huge impacts there, then hurled earthward. Every century or so, a 50-metre-wide asteroid -- like the one that exploded in mid-air above Siberia's Tunguska region in 1908 -- blasts the Earth. Every 5,000 years, a 200-metre-wide rock strikes with the force of a 600-megatonne bomb, capable of destroying an area bigger than a large city. Every 300,000 years, a one- to two-kilometre-wide asteroid crashes, initiating a short-duration global winter. Every 100 million years, a bigger asteroid hits, producing the worldwide calamities that have punctuated evolutionary history.

       The vulnerability of the planet to celestial bombardment is one of the things that drives Ottawa's Richard Grieve. The 56-year-old chief geoscientist at National Resources Canada is a member, along with Balam, of the federal Meteorites and Impacts Advisory Committee. Grieve knows there are 160 big asteroid-impact craters worldwide and that 29 lie in Canada. These range in size from the three-kilometre-wide, million-year-old Nouveau Quebec crater east of Hudson Bay to the 250-kilometre-wide crater at Sudbury, Ont., formed by a monstrous impact 1.85 billion years ago.

       What concerns Grieve is how little effort or money Canada expends on finding out about future dangers from space. Analysis indicates there are some 750 dangerous rocks -- one kilometre wide or larger -- not yet located and another 100,000 big but less threatening NEOs undiscovered. Any one of these would produce a cataclysm.

       We need to learn exactly where near-Earth asteroids are, Grieve believes. "If Balam finds one in advance, maybe we could do something," he says. "Space is relatively empty, but every once in a while..."

       Astronomers, including Don Yeomans, manager of NASA's NEO program, agree that a few months', even a year's warning would not be enough to build and launch a rocket to blow up an NEO or nudge it into a different trajectory. Some say we'd need at least a decade. And the cost would be, well, astronomical.

       For the past 25 years, U.S. spy satellites have recorded high-altitude explosive flashes of incoming meteoroids. Produced by car- to garage-size objects as they enter the upper atmosphere, they are seen as often as 40 times a year. To scientists, their frequency is a warning of the number of NEOs up there.

       The U.S. Air Force and NASA provide more than $4 million in annual NEO funding, including five NEO-dedicated U.S. telescopes: Spacewatch; the LINEAR asteroid-detection project in New Mexico; the Catalina Sky Survey in Arizona; the Near-Earth Asteroid Tracking project in Hawaii; and a survey conducted by the Lowell Observatory in Flagstaff, Ariz. Then there is the International Spaceguard Foundation, centred in Italy, comprising a team of scientists, including Balam, who collaborate through e-mail whenever an NEO observer finds a particularly threatening rock.

       Jeremy Tatum, a University of Victoria professor of physics and astronomy, says that protecting Earth from asteroids should be an international effort -- one that will likely cost $50 million over the next decade to conduct a thorough sky survey.


AS SCOTTI sits in his control room, he thinks back on his reaction to the news that 1997 XF11 wasn't going to pass as close as originally predicted. "Mad as it sounds," he says, "we were disappointed because it would have been a good example of why we should identify these possibly hazardous objects."

THE FIRST NEO to be discovered, in 1989, Eros is described as an "elongated peanut." One of only three NEOs measuring more than ten kilometres wide, the asteroid missed Earth three times this past century -- in 1901, 1931 and 1975 -- coming closest the last time, to within 22 million kilometres of us.
       Taking a break from his nocturnal routine, Scotti climbs a vertical steel ladder, pushes open a hatch in the Spacewatch telescope's dome and stands on a small rooftop platform. In the near distance, crammed on the highest ridge of Kitt Peak, are 22 monstrous telescopes, the largest collection of powerful telescopes on Earth. Far below, the lights of Tucson cluster in the darkness.

       Scotti recounts the time he hiked into Arizona's famous 1.2-kilo-metre-wide Meteor Crater, blasted into the desert 50,000 years ago. He looked up at the walls framing a perfect circle of sky. "I stood there and thought, This hole was caused by a rock only 30 metres wide. And now I'm finding asteroids hundreds of thousands of times bigger. Sooner or later, if we don't remain vigilant, one will hit. It's not if, it's when, and I hope we'll be ready."

       Two thousand kilometres north, in Victoria, Balam works with the latest calculations from the Minor Planet Centre.

       "I get to see what practically no one gets to see," says Balam. "I see supernovas. I see new comets, new asteroids. I sit here and chase rocks. It's a big detective story and a never-ending mystery."

       Balam and Scotti, each inside his cold dome, patiently comparing an endless series of star-filled, asteroid-streaked images, secretly wonder which asteroid will hit -- a strange, apocalyptic waiting game for two night watchmen for planet Earth. For more information on the asteroids in our night skies, visit our web site at

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