Over and out! Rosetta ends mission reunited with Philae on comet’s surface

Over and out! Rosetta ends mission reunited with Philae on comet’s surface

There were emotional scenes at mission control today as space probe Rosetta’s big adventure finally came to an end on the surface of the comet it had been orbiting for two years.

Rosetta’s OSIRIS narrow-angle camera captured this image of Comet 67P/Churyumov-Gerasimenko at 08:18 UT from an altitude of about 5.8 km during the spacecraft’s final descent. Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

At 11.19 UT, the ESA spacecraft ploughed gently into the dust and rubble of Comet 67P/Churyumov-Gerasimenko, 447 million km from Earth.

At the European Space Operations Centre (ESOC) at Darmstadt, Germany, project scientist Matt Taylor responded to the moment with a single word: “Bugger!” Then he told Skymania News: “I didn’t think I would feel like this. We’ve just killed something.”

Surrounded by the world’s media, Matt held his head in his hands, deep in thought before taking the stage. After praising his team, he added: “I don’t know what to say. Rosetta was rock’n roll. It turned everything up to 11. Rock’n roll, Rosetta!”

Rosetta was expected to take its final picture of the 4.7 metre wide oncoming comet from just 5 metres above the surface. Then, as it collided at walking speed, onboard software automatically switched off all the instruments. But the spacecraft was already unable to communicate any longer, because its antenna no longer pointed at Earth.

The landing reunited the mothership with a fridge-sized companion, called Philae, that it had carried piggyback to the comet. Philae touched down in November, 2014, before bouncing twice into a ditch and losing contact. Rosetta came down just a kilometre – less than a mile – from its former companion.

Rosetta was directed to crash-land as gently as possible in a flat region called Ma’at, an Egyptian name in honour of the Rosetta Stone, a stone tablet from the second century BC that allowed 19th century scholars to decipher ancient Egyptian hieroglyphics.

At 9am UK time, the last commands were sent to the spacecraft to fine-tune its trajectory. It allowed mission controllers to calculate the landing time as 11h 19m 8s, UT. (This is the time the final signal was received on Earth after travelling across space – the actual descent ended about 40 minutes earlier.) As the probe sank lower, it was able to observe how comet material became the observed gas and dust.

The comet is a pristine remnant from the material around before the Sun and planets were made, and scientists hope it will unlock the secrets of how the Solar System formed.

The final image taken by Rosetta before its gentle crash-landing. The altitude from which it was taken was still being debated when this article was published. Image credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

On the descent, scientists were keen to get to a zone called the acceleration region, where material ejected by the comet changes from ice to gas, forming the ghostly halo seen around comets’ heads.

Rosetta was one of the most complex and ambitious space mission ever. It became the first spacecraft to orbit and land on a comet, following a ten-year, four billion mile journey through the Solar System. The mission, which launched in 2004, was full of drama. It gained momentum by flying past Earth, taking a stunning crescent image and Mars. On one approach to Earth, it was briefly mistaken for a threatening asteroid!

On the way it flew past two asteroids – Steins in September, 2008, and Lutetia, in July 2010, sending back pictures. Then it went into hibernation in July 2011 to save energy for the final leg of its journey.

In January 2014, to the great relief of the mission team, Rosetta woke up on schedule and “phoned home”. Then, as it neared its target comet, named after the two Ukrainian astronomers who discovered it, they got a big surprise. Instead of resembling a giant snowball, 67P/Churyumov-Gerasimenko looked more like a rubber duck, with two separate lobes.

The next big event was the landing of Rosetta’s fridge-sized companion probe, Philae, which was sent to land on the comet on November 12, 2014. But its harpoons failed to fire and the little probe bounced twice before ending up trapped in a crevasse. Despite that, it sent back valuable data for three days before, unable to receive any sunlight to charge its batteries, it fell silent.

The final part of ESA’s charming Rosetta animation ends with a surprise. Credit: ESA

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During 2015, the comet reached its closest point to the Sun and became highly active, spewing out vast jets of gas and dust which made it too dangerous for Rosetta to get close.

Mission controllers did not know exactly where Philae had ended up, and it was only located earlier this month when Rosetta was finally able to move in and take high-resolution photos. Even so, it was like trying to find a needle in a haystack.

By mission’s end, Rosetta had flown a distance of 7.9 billion km.

Professor Ian Wright, of the UK’s Open University, told Skymania News: “Unquestionably, we have now got data which is going to help us learn more about the origins of the Solar System. The data has been coming down faster than anyone can deal with. It is just piling up. Which is great.

“Will it help us discover the origin of life? Any time you study the chemistry of alien bodies, there is the potential to make some connection. What we will know at the end of the mission is that this was the likely collection of materials from four and a half billion years ago at the start of the Solar System. So if you took that package, along with its inorganic components, and all the rest of it, and then put it in the right environment, is that ultimately how life got started?”

By Paul Sutherland

Paul Sutherland has been a professional journalist for nearly 40 years. He writes regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy, plus he has authored three books on astronomy and contributed to others.

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