Touchdown: Rosetta probe lands on comet 67P

The European Space Agency’s most ambitious mission yet has come to an end as the Rosetta spacecraft collided with the comet’s surface yesterday.

Some space missions go out with a bang, others with a victorious return to Earth, but Rosetta’s final moment was marked simply by radio silence.

After twelve-and-a-half years in space, the European Space Agency spacecraft finally met the surface of the duck-shaped mass of dust, ice and rock, switched off its transmitters and hung up the phone to its controllers on Earth.

Patrick Martin, Rosetta’s mission manager, said: “This is the culmination of tremendous scientific and technical success for this mission. It was historic, it was pioneering and it is revolutionising how we see comets. Farewell Rosetta, you’ve done the job, that was space science at its best.”

Scientists faced a nail-biting 40 minute wait for confirmation that it had touched down and to see the last images captured by Rosetta, taken around 15 metres from the comet’s surface.

The spacecraft touched down on the “head” of the comet at a speed of about 90 centimetres per second - around a walking pace. Mission scientists described this as a “controlled descent” rather than a crash.

Although the surface is soft something akin to the texture of a soft snow-drift - the lander is likely to get damaged in the collision and could even bounce off the surface, as the Philae lander did. Even if its solar panels and other hardware remain intact, the craft has been pre-programmed to shut down its systems on contact, marking the end of a mission that has gripped the world.

Its precise fate will never be known, because Rosetta is now switched off for good and there are no telescopes on Earth powerful enough to see it.

“We won’t know, because we turn off when we touch the surface,” said Professor Mark McCaughrean, a senior science advisor at ESA. “This is space, anything can happen out there ... It’s a bit like does a tree make a sound in the forest if no one is there to hear it?”

Ahead of the landing, the flight team estimated that the craft would impact just 40 metres away from their original target on the Ma’at region of the head, which marked by large pits and “goose bump” structures.

The last images sent back may look like dust-covered rocks, but measurements sent back from Rosetta show that the comet is extremely porous - about 70% of its interior is empty space.

“When you see these beautiful images of the comet you should not think of it as rock,” said Björn Davidsson, a Rosetta scientist based at Nasa’s jet propulsion laboratory. “It’s something like spun sugar or cotton candy – something very, very fluffy.”

Rosetta arrived at 67P/Churyumov-Gerasimenko in August 2014, after spending a decade chasing down the comet.

In the two years since, it has sent back spectacular photographs of the comet’s dramatic landscapes as well as reams of scientific data measuring its composition, density and magnetic field.

In terms of sheer drama, the mission’s climax came when a small robotic probe, Philae, was dispatched onto the comet’s surface in November 2014 to gather surface samples.

Comet 67P is now heading out towards the orbit of Jupiter, and as it speeds away from the sun, Rosetta’s solar power supply was set to run out.

Matt Taylor, ESA Rosetta project scientist, said that rather than hobbling on in a sub-optimal state, the team decided to commit to some final close-up observations. “I’ve seen certain rock bands with certain singers that can’t sing anymore. They should have stopped when they were fully functioning,” he said, ahead of the mission’s end. “And that is what we are doing here with Rosetta. It is maximising what we can do with the spacecraft at this time. This plunge is the only way to get this science.”

These are thought to be the original icy boulders that formed in the solar system more than four billion years ago and then came together to form this comet. In short, the goose bumps are some of the most ancient unaltered objects from the beginning of the solar system. They contain all the ingredients that were available to form life on Earth.

McCaughrean told BBC Radio 4 it was a sad day as he reflected on what the Rosetta mission had achieved

“It’s giving us a real insight into the building blocks of the solar system and the material which could have formed life on the earth, not life itself but the raw building blocks,” he said.

“But more importantly for me, it’s engaged the public in a way which is just unparalleled for a robotics space mission. The enthusiasm I see on the faces of kids around the world when I give talks and the public following online it’s going to be very sad day but a very proud day for everyone that’s been involved.”