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After space junk goes up, it must come down
By Ned Rozell


June 04, 2006

One winter night not too long ago, an Interior musher saw a fireball blazing through the sky "like a flaming Nolan Ryan fastball."

As a baseball fan, I liked his comparison. But that can't be the explanation for the blue flash that lit up the sky. Nolan Ryan retired years ago.

To track down the real cause of the burst of light and the accompanying boom, Fairbanks Daily News-Miner writer Mary Beth Smetzer called the U.S. Space Command at Peterson Air Force Base, Colo. A staffer told her the light show was not the result of anything manmade.

Other space-watchers told her a meteorite probably lit up the sky when it entered Earth's atmosphere and glowed from the sudden friction of air molecules. The meteorite, a fragment of some heavenly body, probably caused a sonic boom as it whistled toward interior Alaska faster than the speed of sound.

That's a good explanation, but I wondered how the people at U.S. Space Command could be so sure our celestial visitor wasn't a piece of old rocket or satellite sucked in by Earth's gravity. Space is crowded with working and non-working satellites, rocket stages containing empty fuel tanks and electrical controls, and other such rubbish. Do the sky watchers at Space Command keep track of it all?


"We have a handle on everything (in space) that's manmade," said Lt. Col. Don Planalp, a spokesman for the U.S. Space Command. "We're tracking about 8,000 different objects that are four inches (in diameter) or bigger."

Space Command knows when a large rocket is launched from anywhere on Earth. Heat-detecting satellites pick up the infrared waves emitted by booster rockets during a launch. Once an object is in orbit, Space Command tracks it with ground-based radar and cameras.

Whatever man lobs into Earth's orbit will someday come down, Planalp said. Of the thousands of satellites blasted into space since the Russians launched Sputnik in 1957, all will eventually return to Earth.

The closer an object circles Earth, the sooner its orbit will meet the atmosphere, a 30-mile thick shell of gases covering the planet. Weather satellites orbit about 300 miles above Earth. Geosynchronous satellites, which carry many of our phone and television signals, are stationed about 22,240 miles away.

Geosynchronous satellites "might be up there for millions of years," Planalp said. Other spacecraft, such as the one used for the Mars Pathfinder Mission, will never return to Earth because they've been blasted beyond Earth's gravitational pull.

Space Command scientists have calculated the orbits of all 8,000 pieces of hardware zooming around the Earth, Planalp said. Though Space Command scientists can pinpoint where manmade space debris will collide with Earth's atmosphere, Planalp said there is no way to predict whether the junk will skip off the atmosphere like a flat stone on water or whether it will plunge to Earth.

If space junk does reach Earth's surface, it probably won't hit your head, your house or your horse.

"There's not much danger," Planalp said. "Seventy-five percent of the earth is water, and much of the remaining 25 percent is uninhabited. The chance of being hurt or of property damage is infinitesimal."

Space Command knows of all the manmade stuff orbiting above us, but the agency doesn't track meteorites, which typically arrive from deep space without pausing to orbit Earth. Along with the aurora, unpredictable meteorites are another good reason to look up when carrying a load of groceries inside on an Alaska winter night. You never know when we'll be treated to another flaming fastball in the sky.


This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell []is a science writer at the institute. This Alaska Science Forum article was published previously.

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