University of Calgary Calgary, Alberta May 31, 2000
Outdoorsman Jim Brook and scientists at The University of Western Ontario (UWO) and the University of Calgary (U of C) have recovered the largest meteorite fall in Canadian history. Analysis shows the meteorite is composed of a very rare material, making it among the most scientifically significant meteorite finds worldwide.
The meteorites fell on the morning of January 18, 2000 in a remote area between Atlin, British Columbia and Carcross, Yukon Territory. A week later on January 25th, a nearby resident, Jim Brook, found the first meteorite fragments while driving homewards on the ice of Taku Arm in Tagish Lake.
Jim Brook describes his discovery, "I was watching closely for meteorites and suspected their identity as soon as I saw them, although I had been fooled several times by wolf droppings. It was obvious what they were as soon as I picked one up, because rocks aren't found on the ice, and I could see the outer melted crust. I was very happy and excited." Darkness soon ended additional meteorite hunting that day, but Jim was back the next morning, collecting several dozen of the space rocks.
Since that find, U of C and UWO researchers, working with the National Aeronautics and Space Administration (NASA), have made several trips to the area to collect samples of the very fragile meteorites and to map the fall area. To date, 500 fragments have been found and hundreds have been recovered from the site -- many still encased in ice.
"This is the find of a lifetime," says Peter Brown, meteor scientist in the Department of Physics and Astronomy at The University of Western Ontario and co-leader of the meteorite recovery investigation. "The size of the initial object, the extreme rarity and organic richness of the meteorites combined with the number we have uncovered make this a truly unique event."
"Of all the times I dreamed of finding meteorites, I never thought of finding them like this," says Alan Hildebrand, planetary scientist in the Department of Geology and Geophysics at the University of Calgary and the other investigation co-leader. "One day while I was picking pieces of meteorite out of porous ice I thought that the experience must be a bit like sampling on the surface of a comet. We believe these to be the most fragile meteorites ever recovered." Initial analysis by Michael Zolensky, a meteoriticist at NASA's Johnson Space Center showed the meteorites were a type of carbonaceous chondrite -- a rare, organically rich, charcoal-like class of meteorites. Zolensky says that his work and that of colleagues "provides indications that the meteorites are unique carbonaceous chondrites with hints of relation to the CI chondrites." Carbonaceous chondrite meteorites make up about three per cent of meteorite finds.
The possible chemical class of this fall constitutes less than 0.1 per cent of all meteorites recovered to date, and represents the most primordial samples known from the early solar system. While the possibilities have researchers very excited, the meteorites' true significance remains to be fully understood. However, Jim Brook's careful collection of pristine meteorites from the icebox of a Canadian winter and subsequent frozen storage has opened brand new doors for meteorite researchers around the world.
The Nomenclature Committee of the Meteoritical Society has officially designated the name Tagish Lake Meteorite for the fall specimens. Using eyewitness and photographic data gathered during the field investigations, and observations from two US Department of Defense satellite systems, the trajectory and velocity of the fireball were determined. The ability to calculate this is a relatively new development in meteorite science -- essentially allowing researchers to determine a meteorite's pre-fall size, orbit and origin in space.
"There have only been four previous meteorites for which accurate orbits are known and no orbits for a carbonaceous chondrite have ever been secured," says Brown. "The entire process of recovery of the material and determination of where it comes from makes this the scientific equivalent of an actual sample-return space mission -- at a thousandth of the cost."
"The Tagish Lake fall is the largest ever recorded over land by the satellite systems," notes Hildebrand. "The recovery of hundreds of meteorites allows studies which will precisely constrain the meteorite's size when it entered the Earth's atmosphere. Calibrating the satellite observations for such a large object will help us understand all the fireballs that the satellites record around the globe, in effect creating a global fireball camera system. These observations will increase our knowledge of both the hazards and opportunities created by the Earth-crossing asteroids and comets."
Background -- The fireball of January 18, 2000 A spectacular meteor crosses the Yukon Territory into northern British Columbia at 08:43 PST. Eyewitnesses reported a brilliant, multicolored fireball that lit up the countryside. Sizzling sounds and peculiar smells that remain to be adequately explained accompanied the fireball. Ground shaking detonations followed a few minutes after the meteor's passage when its sound arrived at the surface. The fireball and its explosions were so stunning that local residents were concerned about the safety of their children and friends. The fireball was also observed by satellites in Earth orbit, maintained by the U.S. Department of Defense (D of D). These observations established an asteroid weighing 200 tonnes and approximately five metres across had impacted the Earth's atmosphere. Data from D of D satellites were available within hours of the event, the quickest any such data have been released after a bolide event by the D of D.
Background -- Discovery of the meteorites While Jim Brook was driving south on the ice of Taku Arm, Tagish Lake, British Columbia, he noticed small dark rocks on the ice. He suspected that these were meteorites from the fireball. He carefully collected the rocks, covering his fingers with clean plastic and placing the meteorites in plastic bags. Brook uncovered almost one kilogram of this material during a total of only a few hours of searching on the lake ice late on January 25 and early on January 26. Snow blankets the area on January 27 ending recovery opportunities. In April, the thaw exposes more meteorites, and a race against time begins. The Taku Arm lake ice would soon melt and ever changing conditions complicated field work. In the first few days less than 10 meteorites were recovered per day. These meteorites were absorbing sunlight and rapidly sinking through the meter-thick ice. The recovery team wondered how much longer meteorites could be found and retrieved. Then searching conditions improved and totals found soared, reaching a high of 94 meteorites in one day.