An uncontrolled satellite is expected to hurtle through Earth’s atmosphere on Wednesday, almost 30 years after it was launched.
The satellite, known as ERS-2, is expected to break up into pieces on reentry, the majority of which will burn up.
Because the reentry is “natural” – in other words, not controlled by humans – it is impossible to predict exactly when and where it will happen, according to the European Space Agency (ESA).
But as the time draws closer, the agency is able to say with greater accuracy what will happen.
It released its latest forecast on Monday, predicting the satellite would reenter the Earth’s atmosphere at 11.14am on Wednesday.
There is a window of uncertainty due to the unpredictable solar activity, which means the reentry could take place up to 15 hours before or after the predicted time.
Photos of the satellite tumbling towards the atmosphere were released by the ESA on Monday.
The images were taken between 14 January and 3 February, when ERS-2 was still at an altitude of over 300km (186 miles).
It is now at an altitude of about 200km (124 mles) and is falling by more than 10km (6 miles) per day, with the speed of its descent increasing rapidly.
When it reaches around 80km, it will start to break and then burn up.
Some fragments could make it to Earth, the ESA said, but will most likely fall into the ocean.
“The risks associated with satellite reentries are very low”, according to the ESA’s information on ERS-2’s reentry.
None of these fragments will contain any toxic or radioactive substances, it said.
ERS-2 was launched in 1995. At the time, it was Europe’s most sophisticated Earth observation spacecraft.
“It provided us with new insights on our planet, the chemistry of our atmosphere, the behaviour of our oceans, and the effects of humankind’s activity on our environment,” said Mirko Albani, head of ESA’s Heritage Space Programme.
After 16 years in orbit, the ESA decided to end its mission and “deorbit” the satellite.
This involved using up the remaining fuel and lowering its altitude from 785km (488 miles) to 573km (356 miles).
This reduced the chance of it colliding with something else in space and cut the time in orbit after the mission ended from more than 100 years to less than 15 years.
