Comet touchdown! Philae and Rosetta make history

Comet 67P/CG as seen by the Philae lander at 3 km above the surface during its descent. The image was taken with the ROLIS (ROsetta Lander Imaging System) instrument designed to study the texture and microstructure of the comet's surface.

ESA’s Rosetta mission has achieved an historic first with the soft-landing of its Philae probe on Comet 67P/Churyumov–Gerasimenko.

After a tense wait during the seven-hour descent to the surface, a signal confirming the successful touchdown arrived on Earth at 16:03 GMT.

“Our ambitious Rosetta mission has secured a place in the history books: not only is it the first to rendezvous with and orbit a comet, but it is now also the first to deliver a lander to a comet’s surface,” Jean-Jacques Dordain, ESA’s Director General, said.

“With Rosetta we are opening a door to the origin of planet Earth and fostering a better understanding of our future. ESA and its Rosetta mission partners have achieved something extraordinary today.”

Cosmos's full coverage of the aims of the mission and its technical brilliance is here.

Rosetta was launched on 2 March 2004 and travelled 6.4 billion kilometres through the Solar System before arriving at the comet on 6 August 2014.

The landing site was chosen just six weeks after arrival based on images and data collected at distances of 30–100 km from the comet.

The seven-hour descent was made without propulsion or guidance. You can see a replay of the mission coverage here.

“One of the greatest uncertainties associated with the delivery of the lander was the position of Rosetta at the time of deployment, which was influenced by the activity of the comet at that specific moment, and which in turn could also have affected the lander’s descent trajectory,” said Sylvain Lodiot, ESA Rosetta Spacecraft Operations Manager.

“Furthermore, we’re performing these operations in an environment that we’ve only just started learning about, 510 million kilometres from Earth.”

The landing encountered one hitch:

Touchdown was planned to take place at a speed of around 1 metre per second, with the three-legged landing gear absorbing the impact to prevent rebound, and an ice screw in each foot driving into the surface.
But during the final health checks of the lander before separation, a problem was detected with the small thruster on top that was designed to counteract the recoil of the harpoons to push the lander down onto the surface. The conditions of landing – including whether or not the thruster performed – along with the exact location of Philae on the comet are being analysed.

The first images from the surface are being downlinked to Earth and should be available within hours of touchdown.

The lander will conduct its primary science mission over the next 60 hours, powered by its main battery. An extended science mission will be possible as long as a rechargeable secondary battery receives enough Sun. There are concerns that dust from the comet on the batteries solar cells may be a problem.

But if all goes well, this extended phase could last until March 2015, after which conditions inside the lander are expected to be too hot for it to continue operating.

Science highlights from the primary phase will include a full panoramic view of the landing site, including a section in 3D, high-resolution images of the surface immediately underneath the lander, on-the-spot analysis of the composition of the comet’s surface materials, and a drill that will take samples from a depth of 23 cm and feed them to an onboard laboratory for analysis.
The lander will also measure the electrical and mechanical characteristics of the surface. In addition, low-frequency radio signals will be beamed between Philae and the orbiter through the nucleus to probe the internal structure.

“Rosetta is trying to answer the very big questions about the history of our Solar System. What were the conditions like at its infancy and how did it evolve? What role did comets play in this evolution? How do comets work?” said Matt Taylor, ESA Rosetta project scientist.

Rosetta’s OSIRIS narrow-angle camera captures a parting shot of the Philae lander after separation.

Philae's parting shot of its mothership Rosetta shortly after separation. The image was taken with the lander’s CIVA-P imaging system and captures one of Rosetta's 14 metre-long solar arrays.
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