The Rosetta spacecraft has collided with a comet
Scientists hope to obtain stunning images and valuable data in the final moments of the descent
Rosetta reached the comet in August 2014 after a 10-year journey
Three months later, the spacecraft deployed a tiny lander, Philae, which landed on the comet
Rosetta has now the lander on the icy surface of the comet signalling the end of the mission
The spacecraft and the comet are heading out towards Jupiter. Light falling on its solar panels is diminishing to the point where it will no longer be able to operate all its instruments
The European Space Agency says operations are going as planned.
Get your one-minute, thirty-second briefing on Rosetta, Comet 67P and today's "landing" - from Rebecca Morelle, external.
Rosetta spacecraft's comet crash landing
Jonathan Amos
Science correspondent, BBC News, Darmstadt
When Rosetta turned towards Comet 67P during the night and on to its collision path, it was moving at about 30cm/s. As it gets lower, the gravity of the icy dirt-ball will pull it in and speed it up. At 2km from the comet, it will be moving at about 60cm/s. At impact it will be about 90cm/s. Walking pace.
All through the descent, instruments are taking measurements and the camera system is firing off shots. The scientists have to box and cox, though. The data rate to Earth is a measly 40kbps.
This is one the latest pictures to come in. It was taken from roughly 8.9km from the comet at 0653 GMT (0753 BST).
Image source, ESA/Rosetta/MPS for OSIRIS TeamAndrea Accomazzo, external has worked on the Rosetta mission for 20 years. No wonder he feels emotionally attached to it.
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What is Europe doing in planetary exploration beyond this comet mission? The Open University's Monica Grady, external tells us what we've learnt at Comet 67P, while Rosetta flight director Andrea Accomazzo, external has a look over the space horizon.
Europe has so much more to explore in the Solar System
The Rosetta probe has had a remarkable 25 months at Comet 67P, sending back extraordinary information about one of the Solar System's icy wanderers. Listen to Tom Fielden, external's review of the mission that ran on the BBC Radio 4 Today programme, external this morning.
The cheers and tears at Comet 67P
Jonathan Amos
Science correspondent, BBC News, Darmstadt
Here's a closer look at that frequency carrier signal. As Chris Lintott explained, this is how controllers will know the impact has occurred because it will simply flatline. Of course, it could also flatline if something goes wrong on the way down. But that's not expected to happen. Rosetta has been told to ignore certain conditions that ordinarily might upset it, such as the ejection of a mass of dust confusing its startrackers. In the past these kinds of episodes have forced the spacecraft into a "safe mode". We don't want that to happen today as it gathers its last-gasp measurements so close to Comet 67P.
The moment of flatline in the control room is still expected at 11:18 GMT; 12:18 BST; 13:18 CEST +/- 2min
Image source, ESAThe spike will disappear on impact
We'll keep you up to date with events as they unfold today on this page, but Chris Lintott, external and the Sky at Night team are also filming a special programme that will go out on Sunday night (22:00 BST) on BBC Four.
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One of Rosetta's big discoveries concerns the origin of Comet 67P. Having studied the probe's detailed pictures, scientists now think the object we see today was actually once two comets that bumped into each other and stuck together. Stephen Lowry from Kent University explains.
Scientists think the comet observed by the Rosetta probe was once two objects
Rosetta is going to hit the comet on its "head". But before it does, it will aim its cameras on some deep pits. It is inside such sinkholes that previous pictures have revealed a lumpy texture on the walls. Scientists think these "goosebumps" may be the icy blocks that originally came together to build the comet billions of years ago. Listen to Mark Bentley, external from the Graz Institute for Space Research, in Austria, explain why these lumps are so important.
The Rosetta probe is aiming to get even better pictures of Comet 67P
The 25 months Rosetta has spent at Comet 67P/Churyumov-Gerasimenko has given us an unprecedented view of one of the Solar System's icy wanderers. Here's a pen portrait of the object that has affectionately become known as the "space duck".
Image source, ESA/ROSETTA/NAVCAMScientists think Comet 67P is actually two comets stuck together
Jonathan Amos
Science correspondent, BBC News, Darmstadt
Rosetta has two main camera systems on board but it will be using the OSIRIS system to acquire descent images. OSIRIS has a narrow angle camera (NAC) and a wide angle camera (WAC). The NAC will lose focus about one km out from the comet; the WAC will start to blur about 200-300m from the surface.
Nonetheless, we should get some remarkable, high-resolution views coming back before impact. The aim is to look inside some pits on the head of 67P where there has been a lot of activity.
The pictures relayed to Earth will be downsized and highly compressed and will need some processing before they are released to the public. How many images will Rosetta manage to get away before it crashes?
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Our science editor David Shukman, external is at mission control in Darmstadt, Germany. He'll have the big final report of the day on the BBC's TV networks.
Rebecca Morelle, external will be reporting live into the TV news channels and on the BBC's radio networks. Follow both on Twitter.
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After successfully turning Rosetta to head down to the comet, controllers then received some pictures back from the probe. These allowed a more refined time to impact to be calculated.
Rosetta should hit the surface at 10:38 GMT+/- 2minutes. This is the time at the comet. It takes 40 minutes for a radio signal to reach Earth (because Rosetta and Earth are separated by 720 million km), meaning confirmation of the collision should be picked up by radio dishes on our home planet at 11:18 GMT; 12:18 BST; 13:18 CEST +/- 2min.
Jonathan Amos
Science correspondent, BBC News, Darmstadt
Controllers here at Esa's operations centre in Darmstadt, Germany, commanded Rosetta to change course late on Thursday. The manoeuvre altered its wide orbit around the duck-shaped icy wanderer and put it on a direct collision course. It is a 19km descent that should lead to the probe hitting the comet's "head" at roughly walking pace at about 11:20 GMT (12:20 BST/1320 CEST) on Friday. A more precise determination of the time will be possible a few hours before impact. The crash velocity will be low, less than a metre per second, but Rosetta was never designed to land and so various components will almost certainly be crushed as it dumps down.
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Jonathan Amos
Science correspondent, BBC News, Darmstadt
On Thursday morning, controllers here in Darmstadt sent up the software patch to Rosetta that will turn it off the moment it hits the comet on Friday.
Currently, the impact is expected sometime after 1200 midday UK time (1300 CEST). And although the probe will be damaged in the collision, it may still be partly functional. To shut it down completely is actually quite hard; spacecraft are designed to fight for life and correct anomalies.
The software patch however will play a trick on Rosetta. As the probe tries to recover itself from the shock of the impact and reboots, its systems will be shunted into a quiescent mode, with the transmitter off. The last time Rosetta was in that mode was when it was being tested on top of its Ariane rocket prior to launch in 2004.