The chances are slim that anyone will see any of the 26 assorted pieces of the Upper Atmosphere Research Satellite (UARS) that are expected to survive reentry into the atmosphere. The chances that someone, somewhere on the planet, will be hit by one of those chunks are 1 in 3,200.
The chance that any particular person (in other words, you) will be hit is infinitesimal: one in many trillions, according to NASA — which had noted on its website as of press time that the satellite would not be flying over North America during the anticipated re-entry period.
But the days leading up to the craft's demise unleashed a flurry of excitement among space enthusiasts who track satellites and a welter of giddy articles about the possible risks.
FoxNews.com offered a widget that allowed readers to track the satellite's progress in real time. Paddypower.com, an Irish gambling website, began taking bets on where the debris will land. Odds of one or more of the pieces landing in Ireland were pegged at 66 to 1, for example.
A poll item on ABC News' website asked readers where they thought UARS would crash. Possible answers were "Harmlessly in the ocean," "In mountains or open plains," or "My house!" As of Wednesday afternoon, "My house!" was leading "In mountains or open plains" by a margin of 2 to 1.
Calm down, satellite watchers say. Stuff falls from the sky every day; big stuff — larger than 1,000 pounds and thus weighty enough to generate debris that falls to the ground — falls about once a week.
"It's business as usual for us here," said Maj. Michael Duncan, deputy chief of space situational awareness at the Joint Space Operations Center of U.S. Strategic Command at Vandenberg Air Force Base, which is tracking the falling satellite for NASA (along with 22,000 other, mostly man-made orbiting objects). He said that he wasn't wholly sure why this particular event was generating such intense attention.
"The UARS reentry hazard is being overhyped," said Don Kessler, a retired NASA senior scientist for orbital debris research.
NASA scientists already know a lot about how UARS, which was placed into orbit by astronauts on the shuttle Discovery in 1991 and was decommissioned in 2005, is likely to meet its end.
The satellite, which monitored ozone and other chemicals in the upper atmosphere for 14 years, is slowing because it is now traveling in low orbit, where it encounters resistance from the upper atmosphere, said NASA space debris scientist Mark Matney. As the density of the atmosphere it is passing through increases, its pieces will eventually break up, lose speed and make their fiery fall.
At press time, forecasters expected that to happen some time Friday afternoon, Eastern daylight time. .
According to NASA, the pieces that could hit Earth — made mostly of titanium, beryllium and stainless steel, and weighing as much as about 300 pounds — will be strewn across a path 500 miles long.
Matney said that the chunks, once bulkhead fittings, fuel tanks and the like, will fall as "oddly shaped pieces of metal" and may be charred or mangled. NASA has warned people not to touch items that might have fallen from UARS because they might have sharp edges, he said. No hazardous chemicals are aboard the satellite, he added.
But there is plenty the trackers don't know about the satellite's reentry — namely, where those pieces will fall — and that's what has some people spooked.
"There is no modeling that predicts where it will hit the surface of the Earth," Duncan said.
Even at two hours before impact, when predictions by the Joint Space Operations Center will be "pretty accurate" in estimating where the craft's orbit will lead, he said, that still leaves an area covering thousands of miles where the pieces could crash down. Weather and other factors could make a difference.
Kessler likens the satellite's descent to a rock skipping across water: Rather than moving predictably, a craft leaving orbit skids across the upper portion of the atmosphere. That makes it hard to know where the bits will fall until a few minutes before impact, he said.
Ted Molzcan, Toronto-based administrator of the hobbyist satellite-tracking Internet mailing list SeeSat-L, said he had hoped the craft would fall near him — but not too near. He saw Raduga 33, a Russian communications satellite, decay and tumble to Earth in 2004, and enjoyed the spectacle.
"Since UARS is fairly large, it will put on a better-than-average show," he wrote in an email. He said the satellite would "look like a surreal comet, with a brilliant head — brighter than any star — and a bright tail … something like a meteoritic fireball, but much slower moving."
UARS' crumbling fragments will glow brilliantly — perhaps enough to be seen during daylight — and will spread along the path of the decay, he added.
Mike Weaver, an aerospace engineer at the Aerospace Corp. in El Segundo who tracks uncontrolled objects leaving orbit and is keeping a close eye on UARS, said that the satellite may light up the sky for as long as two minutes as it makes its way across the sky.
The Chicken Little crowd worries more about getting clocked by a hunk of metal, but if the past is any predictor, that won't happen. "Most of these things fall in the water," said Bill Ailor, another aerospace engineer at the company.
The Russian space station Mir fell safely into the South Pacific in March 2001. The U.S. space station Skylab disintegrated and tumbled into the Indian Ocean and sparsely populated parts of Australia in July 1979.
In fact, over more than 50 years of space flight, just one person is confirmed to have been hit by space junk. In 1997, Lottie Williams of Tulsa, Okla., was brushed by a small bit of metal mesh believed to have come from a spent Delta II rocket.
"I think I was blessed that it doesn't weigh that much," she told NPR in an interview that aired Wednesday. "That was one of the weirdest things that ever happened to me."
Williams did not respond to attempts by The Times to contact her.
The amount of stuff orbiting the Earth is growing steadily, but the threat of satellites falling from the sky may lessen in coming years, NASA's Matney said. Newer satellites are being designed for targeted reentry, or to burn up completely before they hit the ground.
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