Jimmy Westlake: It’s a shooting gallery out there
February 18, 2013
I have a recurring dream that a meteorite lands in my backyard and buries itself in a crater. I run out and sit on top of it, guarding it with a shotgun. Only in my dreams.
For the good folks living in and near the town of Chelyabinsk, Russia, it was no dream. At approximately 9:30 a.m. Friday, a 10,000-ton chunk of space rock entered the Earth's atmosphere and exploded with a blinding flash as bright as the rising sun. The Chelyabinsk meteor was the biggest recorded meteor blast since June 30, 1908, when a similar explosion occurred over a desolate portion of Siberia and flattened hundreds of square miles of forest.
Space rocks are called meteors as they streak through our atmosphere and are called meteorites if they reach the surface of the Earth. The only person confirmed to have been struck by a meteorite fragment was Ann Hodges in Sylacauga, Ala., in 1954. She survived the impact with only a nasty bruise on her leg.
According to NASA meteor specialist Bill Cooke, the Russian meteor was about 17 meters in diameter (about 56 feet) and weighed in at about 10,000 metric tons. It hit the top of the Earth's atmosphere traveling 11 miles per second (about 40,000 mph) and was rapidly decelerated by the air. The temperatures and pressures on the rock became so immense that it exploded while still about 15 miles high, releasing the energy of a 500-kiloton nuclear blast. The shock wave from the blast blew out thousands of windows and toppled some buildings. Miraculously, no one was killed, but more than 1,000 people were treated for injuries, mostly from flying glass. There are no reports of anyone being hit by a fragment of the meteorite.
Searchers found a 20-foot diameter hole in the icy crust of a frozen lake nearby and assumed it was caused by the impact of some portion of the space rock. Divers reportedly found nothing on the bottom of the lake, but tiny fragments on top of the ice might turn out to be surviving pieces of the meteorite.
The Russian meteor apparently was unrelated to the somewhat larger asteroid that buzzed within 17,000 miles of Earth that same day. While asteroid 2012DA14 was moving from south to north across Earth's bow, the Russian meteor was moving in the opposite direction. Just a wacky coincidence.
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There's no doubt about it — it's a shooting gallery out there in space, and Earth is in the line of fire. Earth sweeps up about 50 tons of space debris every day, but almost all of it is in the form of tiny dust specks, nothing like what hit the Earth last week. Astronomers think they have a pretty good lead on all of the space rocks larger than about 1 mile wide that could pose a serious danger to Earth. Small ones like the Russian meteor are virtually undetectable with our current technology. They can sneak up on us at any time. Fortunately, the small ones tend to blow up in the atmosphere before they hit the ground. A 1-mile wide asteroid hardly would be slowed by our atmosphere and would gouge out a crater 25 miles in diameter.
If such an asteroid were discovered to be headed for Earth and we had several years advance notice, we might be able to send a mission, a la "Armageddon," to nudge it into a different path so as to miss Earth. Nuking it to smithereens would not be a good plan, by the way, because we simply would create lots of smaller impactors.
So, I'll just keep waiting patiently for one to land in my backyard.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. Check out his astrophotography website at http://www.jwestlake.com.