Rosetta was never designed to land on the comet - but the mission team have decided to do it anyway.

Why? To end the mission "in a controlled and scientifically valuable way".

Rosetta’s moving alongside the comet away from the Sun – and that means it has less solar power to run things.

"Already, spacecraft operators are having to share the power between the instruments because not all of them can be switched on at the same time any more," Esa said.

"In the absence of sufficient power, further out on its orbit around the Sun, the remaining fuel in the spacecraft would freeze."

So before that happens, the Rosetta team will try to put it down on the comet – and learn what they can.