CAPE CANAVERAL, Fla. — NASA scientists are doing their best to tell us where a plummeting six-ton satellite will fall later this week. It’s just that if they’re off a little bit, it could mean the difference between hitting Florida or landing on New York. Or, say, Iran or India.

Pinpointing where and when hurtling space debris will strike is an imprecise science. For now, scientists predict the earliest it will hit is Thursday U.S. time, the latest Saturday. The strike zone covers most of Earth.

Not that citizens need to take cover. The satellite will break into pieces, and NASA put the chances that somebody somewhere on Earth will get hurt at 1 in 3,200. But any one person’s odds of being struck have been estimated at 1 in 21 trillion.

As far as anyone knows, falling space debris has never injured anyone. Nor has significant property damage been reported. That’s because most of the planet is covered in water and there are vast regions of empty land.

If you do come across what you suspect is a satellite piece, NASA doesn’t want you to pick it up. The space agency said there are no toxic chemicals present, but there could be sharp edges. Also, it’s government property. It’s against the law to keep it as a souvenir or sell it on eBay. NASA’s advice is to report it to the police.

The 20-year-old research satellite is expected to break into more than 100 pieces as it enters the atmosphere, most of it burning up. Twenty-six of the heaviest metal parts are expected to reach Earth, the biggest chunk weighing about 300 pounds. The debris could be scattered over an area about 500 miles long.

Jonathan McDowell, for one, isn’t worried. He is in the potential strike zone — along with most of the world’s 7 billion citizens. McDowell is with the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

“There’s stuff that’s heavy that falls out of the sky almost every year,” McDowell said. So far this year, he noted, two massive Russian rocket stages have taken the plunge.

As for the odds of the satellite hitting someone, “it’s a small chance. We take much bigger chances all the time in our lives,” McDowell said. “So I’m not putting my tin helmet on or hiding under a rock.”

All told, 1,200 pounds of wreckage is expected to smack down — the heaviest pieces made of titanium, stainless steel or beryllium. That represents just one-tenth the mass of the satellite, which stretches 35 feet long and 15 feet in diameter.

The strike zone straddles as far north as Edmonton and Alberta, Canada, and Aberdeen, Scotland, and as far south as Cape Horn, the southernmost tip of South America. Every continent but Antarctica is in the crosshairs.

Back when UARS, the Upper Atmosphere Research Satellite, was launched to study the ozone layer in 1991, NASA didn’t always pay attention to the “what goes up must come down” rule. Nowadays, satellites must be designed either to burn up on re-entering the atmosphere or to have enough fuel to be steered into a watery grave or up into a higher, long-term orbit.