And because timing dictates the location of re-entry, predicting where an object falls is even harder.
”If you’re off by half an hour, you’re on the other side of the planet,” said Ted Muelhaupt, another member of the Aerospace team.
Experts made such a miscalculation in 1979, when the descent of the American space station Skylab captured attention around the world. The station re-entered the atmosphere about half an hour later than expected, landing in the Australian desert instead of over the Pacific, as predicted.
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, is almost entirely over water, though it includes Tasmania and parts of New Zealand, Chile and Argentina. The other, in the Northern Hemisphere, covers more land, cutting across swaths 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 one million times smaller than the odds of winning the Powerball jackpot,” Aerospace noted in the analysis.
Re-entry events like the one predicted for Tiangong 1 are common: Thousands of objects have re-entered the earth’s atmosphere over 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.