Tens of thousands of people across the Prairie provinces and Montana witnessed a close encounter with outer space last November 20 as a 10-tonne meteorite streaked across the prairie sky near the border town of Lloydminster, Alta./Sask., exploding into thousands of fiery fragments on the way down. After it crashed to Earth, Alan Hildebrand, Canada Research Chair in Planetary Science at the University of Calgary, headed to the region to look for evidence.
A member of the Canadian Space Agency’s Small Bodies Discipline Working Group, a volunteer group of scientists who coordinate meteorite reporting and research in Canada, Hildebrand also runs the Canadian Fireball Reporting Centre, where many eyewitness accounts were collected.
Meteorites, fragments of much larger asteroids that typically orbit between Mars and Jupiter, are older than Earth and provide scientists with critical information about the origins of the solar system.
Once recovery efforts of the Saskatchewan fragments resume this spring, it’s expected that more than a thousand rocks will be retrieved — a Canadian record for a single fall.
InnovationCanada.ca (IC): What’s significant about the Saskatchewan incident?
Alan Hildebrand (AH): Fireballs are the light created when meteorites enter the Earth’s atmosphere. In this case, there were enough instrumental records and video recordings of the fireball or of the shadows it cast to determine the atmospheric trajectory, plus the velocity as it entered the atmosphere. Put those together, and you can calculate its orbit. That’s a pretty rare thing. While we have literally tens of thousands of different meteorites in collections around the world, only a dozen are from known orbits. And if you’re trying to sort out the structure of the solar system, you’d naturally like to know what kind of material is falling from which orbit.
IC: So you’re confident you can add to that dozen?
AH: Yes. We already have a good idea of the trajectory. We just need to do some other checking and work with the videos to get the velocity. So it’s looking pretty good.
IC: What causes meteorites to break off asteroids, and how often do they reach Earth?
AH: It’s almost always because of impacts. For example, a smaller asteroid hitting a larger one. The Saskatchewan meteorite is likely a fragment of a large impact we think happened in the asteroid belt eight million years ago. As for frequency, about 140 meteorites land in Canada each year. But in all of Canadian history, only 76 meteorites have actually been found.
IC: What’s your role when there’s a fireball sighting?
AH: As coordinator of the Fireball Reporting Centre, I collect the witness accounts and send a summary to the committee, recommending further action if warranted. Because this one was big, I went out a couple of days after the incident to try to figure out where it landed. We try to get eyewitness reports and security-camera data as quickly as possible — before memories fade or the data are erased — and then piece together information that helps us track the meteorite-strewn field.
IC: So you’re like a meteorite detective?
AH: Yes, it is like detective work. And researchers like that kind of thing — teasing Mother Nature’s secrets away from her.
IC: Meteorite falls tend to be harmless, but that isn't always the case with asteroids. You’re well known for your role in identifying the Chicxulub crater, created 65 million years ago by an eight-kilometre-wide asteroid that was responsible for killing off the dinosaurs. Have other asteroids of that magnitude hit Earth?
AH: Yes, a couple, but they were much older. They go back two billion years, so we don’t know if there were any associated effects.
IC: How big do asteroids have to be before we start worrying about them?
AH: Not very big. It depends where they hit. If something like a 30-metre rock, which is a pretty small asteroid, were to explode over Calgary, it would literally flatten the city and kill everyone in it. On the other hand, if it exploded over the Pacific Ocean, there would be zero fatalities or damage to the planet.
IC: You also head up the scientific team for the Near Earth Object Surveillance Satellite (NEOSSat), a tracking telescope the Canadian Space Agency and Defence Research Development Canada plan to launch into Earth orbit in 2010. Is part of its role to track asteroids that endanger us?
AH: NEOSSat will allow us to look for asteroids we can’t see from the ground. Ideally, we would like to know where all the asteroids in near-Earth orbit are and understand their origins, what they can teach us about the history of the solar system and the evolution of the asteroid belt. We’d like to know their composition as potential resources and exploration targets. And we’d also like to evaluate the impact hazard. Is anything big going to hit us soon?
IC: What could we do with that information?
AH: If we go back to that hypothetical asteroid heading for Calgary, we could evacuate the city with enough advance notice.
IC: Any other way we could intervene?
AH: If we had years of notice about a big one coming at us, then, yes, we could contemplate going into space and moving it out of the way.