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

ERS-2, which weighs about as much as an adult male rhinoceros, could re-enter about 15 hours earlier or later than expected, according to the space agency. The agency cannot predict exactly when and where the satellite will enter Earth's atmosphere because its return is "natural."

What is a natural return?

ERS-2's batteries were depleted and its communication antenna and onboard electronics were switched off, which means there's no way to actively control the motion of the satellite from the ground during its descent, the European Space Agency said. The last of ERS-2's fuel was used up back in 2011 to minimize the risk of a catastrophic explosion capable of generating a large amount of space debris. 

Is there any danger as ERS-2 returns?

Most of the satellite will burn up as it re-enters Earth's atmosphere, with some remaining fragments likely to fall into the ocean, according to the space agency. None of the fragments will contain any toxic or radioactive substances.

The space agency added that the annual risk of a person being injured by space debris is under 1 in 100 billion, or 65,000 times lower than the risk of being struck by lightning.

What was ERS-2 doing in space?

The satellite was launched on April 21, 1995 as an Earth observation spacecraft. It was used to collect data on Earth's land surfaces, oceans and polar caps. ERS-2 was also used to monitor natural disasters, such as severe flooding and earthquakes.  

Its mission ended in 2011, when the European Space Agency began deorbiting the satellite. The deorbiting process helps prevent collisions in orbit and mitigates the creation of space debris. 

ERS-2's remaining fuel was used up as it was deorbited. The satellite's average altitude was also lowered so it could safely re-enter Earth's atmosphere within the next 15 years.