A hefty, unneeded component that astronaut Clay Anderson last year heaved off the International Space Station now is coming down to Earth, with reentry and an impact area unknown.

The object, an ammonia-filled cooling unit, is about the size of a refrigerator. But it weighs 1,400 pounds on Earth, almost 10 times more than a brand-new refrigerator.

It was unneeded on the space station, becoming unwanted trash, and there was no room on space shuttles to return it to Earth. So Anderson, standing at the end of a robotic arm, chucked it into the void, where the cooling-unit orbit has decayed slowly every day since. Now it’s about to make the final plunge into reentry.

Space officials are unsure just where the unit will hit the atmosphere, and also are unsure just where any chunks of the unit surviving reentry might come to ground.

Since water covers about two-thirds of Earth, however, chances are better than even that no chunks will harm people.

The United States earlier used a modified ballistic missile defense system to shoot down a reentering, failed spy satellite because it contained hydrazine propellant, saying any parts of the satellite — but especially the tank filled with hydrazine — could harm people if fragments came down on land.