2016-09-30 10:54:09
Rosetta Spacecraft to End Mission by Sinking to Its Comet Companion

10:54, September 30 193 0

Rosetta, the first spacecraft to orbit a comet, is now falling toward its companion of the last two years.

Its minutes are numbered.

Rosetta fired a small thruster for 3 minutes 28 seconds on Thursday to set it on a path that will intersect with Comet 67P/Churyumov-Gerasimenko, its object of observation since August 2014.

At 6:40 a.m. Eastern time on Friday, give or take 20 minutes, Rosetta will do a soft belly-flop onto the comet, closing what is arguably the most ambitious and successful mission ever attempted by the European Space Agency. The radio signal confirming Rosetta’s demise, will arrive on Earth about 40 minutes later, or close to 7:20 a.m.

The European Space Agency is webcasting the final minutes from the mission operations center in Darmstadt, Germany.

Before it goes silent, it is collecting and sending back one last batch of images and data.

Rosetta’s journey will conclude with quite a few firsts, and quite a few fans.

Comets are frozen remnants that hold secrets about the early solar system, and Rosetta was the first spacecraft to do more than just whiz by one. Comet 67P, which likely formed outside of Neptune, was one of the few with an orbit that could be matched by a spacecraft.

Two years of observation have revealed a dormant comet coming to life as it neared the sun and heated up, shooting geysers of dust and gas off its surface. Scientists learned that its shape, resembling a rubber duck, most likely occurred when two comets bumped into each other at a low velocity and stuck together.

The European Space Agency created a series of cartoon videos for children. For an older audience it commissioned a short film, “Ambition,” which starred actors from the HBO series “Game of Thrones.” Aidan Gillen, who plays Petyr “Littlefinger” Baelish, and Aisling Franciosi, who plays Lyanna Stark, explained the mission’s grand goals with sci-fi storytelling:

The film was released in October 2014, shortly before Rosetta dispatched a small lander, Philae, to the surface of Comet 67P. On Wednesday, the space agency released an epilogue:

After making its closest approach to the sun in August 2015, Comet 67P is now on the outward leg of its orbit. As sunlight grew more faint, Rosetta was less able to generate power from its solar panels.

Mission managers decided on a swan dive to collect one last batch of data: close-up observations of mysterious pits that appear similar to sinkholes on Earth.

The camera might be able to make out features as a small as 1-inch wide.

“It will be interesting to get to look into the interior of the pits,” Mohamed Ramy El-Maarry, a postdoctoral researcher at the University of Bern in Switzerland, and a member of the team working with Rosetta’s high-resolution camera, said during a news conference on Thursday.

Because Rosetta was never designed for a landing, its transmitter will be turned off as soon as it touches down and the stream of data will come to an end.

The instrument that collected and studied dust particles has already been turned off; there would not be enough time for it to analyze the data before impact.

During a series of presentations on Thursday, mission scientists described some of their findings, including a variety of “magical landscapes” along with an overall emptiness. They released audio of a “cosmic song,” created by the magnetic fields oscillating in the trail of particles flying off the comet.

Valerie Ciarletti of the Université Paris-Saclay, who helped investigate the comet’s interior with radio waves, said the inside of Comet 67P is about as porous as fresh, powdery snow — 70 percent of the volume is empty space. “It’s very fluffy material,” she said.

Parts of the surface, like the rocky region where Rosetta’s lander Philae wound up, are more dense, with a porosity lower than 50 percent. “It could be something like sand,” Dr. Ciarletti said.

The interior was also homogeneous. There were no big caves or large regions of compressed material.

Thurid Mannel, a scientist at the University of Graz in Austria, described a menagerie of dust particles spanning a wide range of sizes and materials. Many were shattered by the impact with the device on Rosetta that collected dust particles ejected from the comet. “The dust is very, very fragile,” she said.

The scientists learned much about the comet’s landscape. Dr. El-Maarry described its surface as very dark — reflecting just 3 to 4 percent of the sunlight that hits it. The darkness comes from a dearth of ice at the surface and an abundance of organic molecules.

Some areas are bare rock; others are smooth terrains buried in dust. “You can think of something like a sea of sand being surrounded by cliffs,” Dr. El-Maarry said.

The rocks are cracked with fissures.

“Anywhere we can see that surface and we have good enough resolution, we see fractures everywhere,” Dr. El-Maarry said.

Charlotte Goetz of the Technical University Braunschweig was among the scientists who studied the cloud of charged particles around the comet. When Rosetta first arrived, the interplay of particles from the comet with the solar wind produced oscillations in the magnetic fields that the scientists turned into sound, a “cosmic song.”

Closer in, as more material spewed off the comet, the tune changed. Dr. Goetz on Thursday presented a longer song.

But then as Rosetta and the comet moved away from the sun, the original song returned.

At the end of Thursday’s presentations, Matt Taylor, the project scientist, thanked the other scientists who he said “worked their guts out to get to where we are today.”

He said they had mixed feelings: sad that Rosetta’s demise is imminent, and that they have just scratched the surface of analyzing the data.

”The operations end,” Dr. Taylor said, “but we still have all this science to do, so they’re still happy that we got to this stage.”