Rosetta probe ends comet mission with a bang

The European Space Agency’s Rosetta spacecraft descended to a gentle mission-ending crash landing on comet 67P/Churyumov-Gerasimenko early Friday, beaming back a final series of increasingly detailed pictures and other data before shutting down on impact, closing out an unprecedented voyage spanning more than 12 years and nearly five billion miles.

The centerpiece of a $1.6 billion mission, the spacecraft sent its final bit of data at 6:39:28 a.m. EDT (GMT-4). But that final radio transmission near the moment of impact took 39 minutes and 51 seconds to cross the 447-million-mile gulf to Earth, reaching ESA’s control center in Darmstadt, Germany, at 7:19:19 a.m.

On a large video monitor, the realtime presentation of the signal, normally seen as a sharp, well-defined spike, suddenly vanished, marking the end of ESA’s most ambitious space mission.

“This is it. I can announce full success of this historic descent of Rosetta towards 67P, and I declare hereby the mission operations ended for Rosetta,” said Patrick Martin, the mission manager.

“Flying to a comet and around a comet for over two years, as close as a few kilometers and more than 500 million kilometers from Earth, is a challenge,” he said. “And we’ve done it. This tells you that we’ve got the right people here, the best people you can get to do this job. And we are very proud.”

• 5 cool things Rosetta has learned about comet 67P
  

Launched in 2004, Rosetta has been flying in formation with 67P/Churyumov-Gerasimenko since its arrival in August 2014, dropping a small lander to the surface three months later and then devoting more than two years to close-range observations with a battery of 11 sophisticated instruments.

But with comet now heading away from the sun, Rosetta’s solar panels could no longer generate the energy needed to continue powering all of its instruments and subsystems. So mission managers decided to order the spacecraft to end its life with a crash landing, hitting the surface of 67P at about two miles per hour, or walking pace.

While a relatively soft landing, Rosetta was not designed to touch down, and its computer was programmed to shut the spacecraft off at the moment of impact.

But all the way down, it’s cameras were recording the scene below in increasing detail, paying particular attention to a deep pit known as D1, one of many on the comet that can be a football field wide and equally deep. 

The walls of these pits appear to be made up of countless spherical bodies nicknamed “goosebumps,” or “dinosaur eggs.”

“They’re very important,” said Bonnie Buratti, a U.S. project scientist at NASA’s Jet Propulsion Laboratory. “Prior to this mission, our whole idea about the formation of the solar system, how the planets formed, was very hand wavy, like ‘here’s this cloud of gas and dust, it collapses and then somehow miraculously these planetesimals, these things that are basically the comet, formed.’

“It looks like these dinosaur eggs are the small particles, a few meters wide, they’re conglomerations of the dust from the interstellar cloud that collapsed. (That material) formed these dinosaur eggs, these boulders, that gravitate and then get bigger and bigger and finally form planetesimals.”

Comet 67P/Churyumov-Gerasimenko, scientists now believe, “is made up of these smaller objects, smaller planetesimals, that we have jokingly called dinosaur eggs,” Buratti said. “I think that’s a great discovery, that we kind of see the progression of how these planetesimals were put together.”

The final sequence of images from Rosetta were slightly out of focus, as expected, as the spacecraft slowly descended to lower and lower altitudes than ever anticipated for normal operation. But they clearly showed a pebble-strewn surface with clearly defined rocks of all shapes and sizes where Rosetta finally touched down.

“Today is a very sad moment for me,” said Roger Bonnet, a former ESA science director. “It’s like cosmic euthanasia, you just pulled the plug. But this mission has been a dream. ... Rosetta is now on the nucleus. It’s a sleeping beauty. Let me wish that a charming prince, a Prince Charming, will come one day, maybe from ESA or NASA, to wake it up!”

NASA contributed three of Rosetta’s instruments and provided its Deep Space Network to send commands to the spacecraft and receive its signals. NASA’s acting science chief, Geoffrey Yoder, congratulated his ESA counterparts on the success of the mission and praised the cooperation between the two space agencies.

David Southwood, former director of science and robotic exploration for ESA, spoke next and said simply “It’s all over.”

“I was delighted to hear about the cooperation with the Americans, that’s terrific,” he said. “But I’m going to say this with an English accent. This was European through and through. It was a European launch, it was European operated and we just finished in a gentle European approach to comets. You do it your way, we do it our way!”

He was jokingly referring to NASA’s Deep Impact mission, which crashed a heavy, fast moving “impactor” into the surface of another comet, 9P/Tempel, in 2005, blasting out debris so it could be studied by the parent spacecraft.

But Rosetta is in a class by itself, with 672 scientific papers published to date, including 190 this year alone. Another 50 are in work.

“Rosetta’s blown it all open, it’s made us change our ideas of what comets are, where they came from and the implications of how the solar system formed and how we got to where we are today,” said Matt Taylor, Rosetta project scientist.

“And it’s important to know Rosetta mission is both the lander and the orbiter, together they have made it possible to do the science, to make the breakthroughs that we have,” he said. “And we’ve only just scratched the surface. We have decades of work to do on this data. So the spacecraft may end, but the science will continue.”

Buratti said the spacecraft’s observations prove that comets are among the oldest bodies in the solar system, an intermediate step in the slow build-up of planets.

“We’re pretty certain, about as certain as you can get in science, that we really are looking back at the formation period of the solar system,” she said. “The two small bodies that make up this comet, and we call them planetesimals, are almost certainly primordial, dating from the early phases of the solar system. They don’t seem to be processed in any way. These are truly the building blocks from which the planets were formed.”

In addition, Rosetta found organic compounds in abundance, including the amino acid glycine. Scientists believe complex organic compounds must have originally formed in the outer solar system and probably made their way to Earth in comet impacts.

“You can’t form organic molecules, the building blocks of life, in the inner solar system where the Earth is because it’s just too hot,” Buratti said. “They form in the outer regions of the solar system, these complex molecules that have carbon, hydrogen, oxygen, nitrogen, potassium, the things that life needs to form and to be sustained.

“It’s believed that they are formed in the outer solar system and brought into the Earth by comets. And we saw many of these molecules on 67P, including glycine, the amino acid.”