A satellite weighing about as much as an adult male rhinoceros is set to re-enter Earth's atmosphere today, but scientists don't know exactly when or where.

A satellite will likely make an uncontrolled return through Earth’s atmosphere today, according to the latest estimates from the European Space Agency.

It says ERS-2, which weighs about as much as an adult male rhinoceros, is expected to re-enter at about 11:32 a.m. EST — plus or minus 4.6 hours. The agency can’t predict exactly when and where the satellite will re-enter because its return is “natural.”