UND expert: Meteors common, but Russian one was rare

A meteor exploding over Russia Friday sent out a glass-shattering shockwave from 30 miles up in the air, but sent waves of excitement through the Space Studies Department at the University of North Dakota in Grand Forks.

Hundreds of small meteors enter Earth’s atmosphere each week, but ones like the estimated 7,000-ton Russian object are a rarity, according to space studies professor Mike Gaffey.

“These are natural events that occur all the time,” he said. “But then you have big ones like this that draw a lot of attention.”

Pierce County has had its own meteorite visitor, though it was hundreds of millions of years ago. A meteorite struck the earth near where Nugget Lake County Park is now, and some evidence of the hit remains.

NASA estimates last week’s meteor was 49 feet wide before it broke up in the atmosphere. The resulting shockwave destroyed windows and sent glass flying — injuring about 1,100 people.

Gaffey said the explosion produced a force equal to 10,000 tons of TNT — about 5,000 tons shy of the atomic bomb dropped on Hiroshima in 1945.

“It’s a rare and spectacular event,” he said. “But lucky for us they are rare.”

Meteors weighing about 5 tons or less enter the atmosphere every day, but often burn up before hitting the ground, according to Gaffey. Others land in the ocean or rural areas where they go unnoticed.

If pieces of the Russian meteor did make it to the ground, they could provide researchers with more information about a variety of topics such as the geology of other planets and the formation of the solar system.

North Dakota has had its own run-in with a large meteorite. The Red Wing Creek structure is a prehistoric crater located about 15 miles southwest of Watford City.

The approximately 6-mile wide crater is not visible to passersby because it is buried under about 6,000 feet of rock. It is estimated to be 200 million years old and major oil deposits were discovered there in 1972, according to Gaffey.

Other-worldly visitors are common — except the really big ones

Cosmic debris rains down through the atmosphere nearly every day, accumulating at a rate of 37,000 to 78,000 tons per year. While that may sound like a lot, much of it is dust or passes unseen over the oceans.

At least a half dozen times a year, however, a fireball burns up over a populated area and drops meteorites. Their fall is pinpointed by careful analysis of the angle of entry based on eyewitness reports, Doppler weather radar, security cameras or even dashboard cams, as we saw in Russia on Friday.

Once the word is out, everyone from those closest to the areas of impact to meteorite hunters from across the planet are eager to find a piece of otherworldly treasure.

What they’re looking for are leftover fragments from collisions of bodies in the asteroid belt between Mars and Jupiter. Over the eons, Jupiter’s gravity nudges the shattered rocks out of the belt, sending them toward the inner solar system. Millions of years later, those fragments may hurl toward Earth.

As the space rocks plummet through the atmosphere, the heat and pressure become so intense that even a fairly large object, say 13 to 50 feet across, will more often than not burst into harmless pieces that fall to the ground as meteorites.

A 13-footer hits our planet about once a year. One the size of Friday’s fall in Russia — about 50 feet across and weighing around 7,000 tons — strikes Earth about once every 50-60 years. The bigger they are, the less frequently they fall but the greater the consequences.

Yesterday’s flyby asteroid 2012 DA14, unrelated to the Russian fireball, is about 150 feet across and would cause regional devastation if it struck. One that size only rings our bell every thousand years. An asteroid of about 0.9 miles across could cause planetwide devastation and climate change. The good news is such an event happens only once in half a million years.

While most of the 0.9 mile and larger near-Earth asteroids have been discovered, there are something like a million others as big as the one that zoomed by harmlessly yesterday. Sky surveys have ferreted out many of them, but many more remain to be found — before they find us.

Follow the Astro Bob blog at http://astrobob.areavoices.com.

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