A Fiery Entrance: Meeting the Meteor
(Posted February 27, 2013)
A 10,000-ton meteor recently exploded in the sky over Russia, injuring over 1,000 people and sparking discussion about the earth's safety from meteors. Matt Beaky, assistant professor of physics, answers some questions about this space visitor:
Q: What is the correct term for this phenomenon?
A: Asteroids are things that are in orbit around the sun. There's no size restriction. They could get down to a few centimeters, I suppose. For an asteroid, we usually think of a few meters or bigger. Meteoroids are space rocks that will eventually collide with the earth or enter the earth's atmosphere, so an asteroid could become a meteoroid. When it hits the atmosphere and starts to burn up, that's a meteor. The streak you see in the sky is the heated rock. Most of them are tiny, grain-of-sand sized, but some are bigger obviously. When it hits the earth, the bits of rock left over are meteorites. The term bolide refers to a meteor or a streak of light in the sky that is especially bright, also called a fireball. And again, there's no definition of how bright it has to be to be a bolide.
Q: How common are meteors like the recent one in Russia?
A: Pretty uncommon. We don't have great historical records, but maybe a few times a century. Historically speaking, there may well have been meteors that exploded in regions that were unpopulated or over the ocean where no one ever saw them. It's hard to get an exact count. The ones we know about appear only a couple times a century.
Q: Why wasn't this meteor predicted beforehand?
A: We try to predict them. There are telescopes that search the sky for little bits of rock, looking for reflected sunlight from these rocks. The smaller they are, the less they reflect, and the harder they are to see. The one that exploded over Russia was quite small, I think about 15 meters across, so it didn't reflect much light at all. It would be a very dim object. What made this one especially difficult was that it came from the direction of the sun, so you would have to look in the daytime sky to see it at all, and it's pretty much impossible to see against the glare of the daytime sky.
Q: What is the likelihood of a meteor entering the earth's atmosphere and causing major damage?
A: I don't have exact odds, but here have been two in the past century. There was the Tunguska event in 1908, also in Russia. That was actually much more powerful than the one that exploded earlier this year. With the recent event over the town of Chelyabinsk, injuries were caused entirely by the shockwave, exploding glass and things like that. The one over Tunguska didn't cause any human injuries that we know of, so the odds are pretty slim for major damage. It's not worth staying up nights worrying about. There are many risks that we encounter every day that are much more likely to be a concern.
Q: How concerned should we be?
A: It's prudent to identify possible risks. When it's something as relatively simple as building a network of telescopes with the capability to identify small objects that might intersect with Earth's orbit, that's a fairly small cost. Chances are we won't find anything, but if we do the payoff is big. I think we should be cautious and take the steps we can take to predict these types of events, but an individual worrying about it won't do any good.
~Laura Bitely '14, Juniata Online Journalist
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