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Chinese space station to crash to Earth, but nobody should worry
By Niraj Chokshi
New York Times

Sometime around the start of spring, a 9.4-ton Chinese space station is expected to come hurtling back to Earth.

The space station, Tiangong 1, is predicted to make that return trip in mid-March, give or take a few weeks, according to an analysis by the Aerospace Corp., a federally funded research and development center in California. But don’t worry: Odds are no one will be hurt.

“It most probably will not harm anyone,’’ said Andrew Abraham, a member of the team behind the analysis. “The odds of being struck by a piece of this space station as it’s reentering are exceptionally tiny.’’

While the researchers are confident that humanity will probably be spared, their ability to pinpoint specific details about the reentry is limited.

Any prediction about when an object will return from space must factor in multiple variables, including the density of the upper atmosphere as well as the object’s speed, location, orientation, and physical properties, the researchers wrote. Predicting where an object will reenter the atmosphere is even harder.

Tiangong 1, which has been unmanned for more than four years and whose name means heavenly palace, could fall anywhere on about two-thirds of the Earth’s surface, although it is most likely to land in one of two bands that encircle the globe parallel to the equator, the researchers said.

One of those regions, in the Southern Hemisphere, includes Tasmania and parts of New Zealand, Chile, and Argentina. The other, in the Northern Hemisphere, covers more land, cutting across part of the United States, Europe, and Asia.

But even in those areas, the likelihood that anyone will be hit by part of the station is incredibly low.

“The probability that a specific person (i.e., you) will be struck by Tiangong 1 debris is about 1 million times smaller than the odds of winning the Powerball jackpot,’’ Aerospace noted in the analysis.

Reentry events like the one predicted for Tiangong 1 are common: Thousands of objects have reentered the Earth’s atmosphere during the past half-century, according to Aerospace.

That includes dozens of large objects each year.

As they come flying back to Earth, the objects compress the air beneath them, generating intense heat, up to 3,000 degrees Fahrenheit, according to the researchers. That heat and pressure can cause the objects to break apart, melt, and vaporize, leaving little left to reach the Earth’s surface.

“We know that most of it will burn up in the atmosphere as it starts to break apart,’’ said Roger Thompson, another member of the Aerospace team behind the analysis.

Even when objects survive the fall, they rarely cause substantial harm. Only one person is known to have been hit by such debris: Lottie Williams of Oklahoma was struck without injury by a small chunk of a rocket booster in 1997.

The largest manufactured object to return to Earth was the 134-ton Mir space station, which crashed into stormy waters about 1,800 miles east of New Zealand in March 2001. Tiangong 1, at 39 feet in length, doesn’t even rank among the 15 largest objects to make reentry, according to Aerospace statistics.

The station was launched in late 2011 with plans for it to remain in orbit for just two years. After periodically adjusting its altitude until Dec. 16, 2015, Tiangong 1 has slowly been falling since then, Aerospace said.

China announced in March 2016 that it was no longer in contact with the station, suggesting that its return is likely to be uncontrolled, according to Aerospace. After two manned visits to Tiangong 1, there have been no astronauts aboard the station since 2013.