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(Image: ESA/ATG medialab)

The European Space Agency has announced that Philae has detected organic molecules on comet 67P 鈥� and there are many more scientific discoveries to come

Landing on a comet was never going be easy. Last week, the European Space Agency鈥檚 Philae spacecraft, the first robotic probe designed to grapple and drill a comet, bounced and skidded its way across the alien surface before settling in for what might be a long nap. The excitement of the landing may be dying down, but researchers are just beginning to take stock of events 鈥� and Rosetta, Philae鈥檚 mother ship, might even get its own chance to touch the comet.

鈥淢ankind had an outpost on the surface of a comet working for three days,鈥� says Rosetta flight director . 鈥淎 few things didn鈥檛 work exactly as we wished, but we knew that the risk was tremendous.鈥�

Rosetta spent a decade flying to comet 67P/Churymov-Gerasimenko, and spent three months mapping its surface to prepare for Philae鈥檚 touchdown.

That historic landing happened on 12 November, as the world watched.

鈥淲e are there and Philae is talking to us,鈥� said lander manager from the European Space Operations Centre in Darmstadt, Germany. 鈥淲e are on the comet!鈥�

But the landing didn鈥檛 go as planned. The three systems designed to attach Philae to the surface 鈥� a gas thruster, harpoons and ice screws 鈥� all failed, so the spacecraft bounced twice before coming to a halt, angled against a shadowed cliff with one leg in the air. Without enough sunlight to recharge its batteries, Philae went into a deep sleep. There is a chance it could revive as the comet moves closer to the sun, but for now researchers are busy dissecting the wealth of data Philae managed to upload before it shut down.

Life鈥檚 origins

Rosetta and Philae were charged with discovering whether life on Earth was kick-started by comets. These icy space rocks are leftover material from the cloud of dust and gas that formed our solar system 4.6 billion years ago, so investigating them gives us a peek at the pristine building blocks of planets. What鈥檚 more, comets may have rained down on Earth after it formed, providing water and other molecules necessary for life.

Despite its brief time on the surface, all 10 of Philae鈥檚 instruments took readings in an attempt to tackle this question, although it is still unclear whether the botched landing means some failed to gather meaningful data. The lander鈥檚 two sets of cameras returned dramatic pictures of its descent and landing, which will help uncover the comet鈥檚 composition. CONSERT, a radar system shared by Philae and Rosetta, probed the internal structure of the comet, and was also jury-rigged to help track Philae as it bounced across the surface.

The lander wasn鈥檛 able to run through a preprogrammed sequence of investigations, so the team had to choose which instruments to activate first. Any with moving parts could have jolted the spacecraft, jeopardising its tenuous hold on the comet.

Desperate hammer

A suite of instruments called MUPUS that included a probe and hammer was one of the first activated. It took the comet鈥檚 temperature at a frigid -153聽掳C, but had trouble with the hammer. The team ramped through three modes to a fourth 鈥渄esperate mode鈥�, which broke the hammer after 7 minutes, without cracking the surface. The team says that under 10 to 20 centimetres of dust, the comet is as hard as ice, which could explain why Philae bounced.

The final and most risky operation was switching on Philae鈥檚 drill. The drill was supposed to dig 25 centimetres into the surface and return samples to two other instruments: COSAC, which analyses organic molecules to determine their shapes, and Ptolemy, which investigates molecular isotopes. Since ESA didn鈥檛 know exactly how Philae was positioned, it wasn鈥檛 clear if the drill could actually reach the surface. And with battery running out, there was only time to extract a single sample 鈥� one instrument would have to go without.

In the end ESA decided to give the sample to COSAC, which can identify whether organic molecules are left or right-handed. Both types are produced in equal amounts through chemical processes, but for some unknown reason, life on Earth contains only left-handed molecules. A particular chemical reaction on comets could be responsible for the imbalance. Researchers are still working to confirm whether the drill did indeed extract a sample, although ESA says COSAC has identified organic molecules in the gas around the comet.

, who is in charge of Ptolemy, says some surface material entered that instrument鈥檚 sensors during the bounce. 鈥淲e did a scratch and sniff,鈥� he says. 鈥淲e鈥檝e got measurements from two different places on the surface.鈥�

Absolute success

Rosetta mission manager says the landing was always given only a 75 per cent chance of working. 鈥淲e always knew we could end up on a slope and then the drill wouldn鈥檛 work,鈥� he says, though he concedes potentially losing the chance to sample beneath the comet鈥檚 surface will be a blow. On the flip side, landing in two places has let them study multiple points on the comet. 鈥淔or me this is an absolute success on such a daring enterprise.鈥�

As of 18 November, ESA was still trying to identify Philae鈥檚 final resting place. Pinpointing its landing spot should help calculate when the craft is most likely to be revived.

Accomazzo thinks the odds are low, 鈥渕ore than 1 per cent and less than 50鈥�. But Ulamec is more optimistic. 鈥淚鈥檓 very confident that Philae will resume contact with us and that we will be able to operate the instruments again,鈥� possibly in the spring or summer of 2015, he said.

Rosetta itself could one day join Philae on comet 67P. The orbiter will run out of fuel at the end of 2016, and ESA must decide whether to put it into hibernation, or put it down on the surface.

A large flat area on the dark side of the comet was not an option for Philae, but it will be well illuminated by 2016. Rosetta could crash-land there, taking extreme close-up pictures of the comet and sniff its atmosphere on the way down. 鈥淚f we are called to do something like this I would be pleased,鈥� says Accomazzo. 鈥淚f you ask me personally, I wouldn鈥檛 do anything else.鈥�

This article will appear in print under the headline 鈥淲eekend on a comet鈥�