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Devangshu Datta: Rosetta-Philae – To more answers and beyond

Philae’s landing on Comet 67P Churyumov-Gerasimenko (C67P/C-G) was the culmination of a 10-year odyssey for the robotic Rosetta Orbiter. The landing went through and some of Philae’s systems stayed functional, despite landing equipment failure and two bounces.

Whether the Lander stays grounded and operational is a different matter. The mission has already been a big success as the first controlled landing on a comet. As Philae runs its scientific payloads, it will collect lots of data to test and flesh out some key hypotheses.

Geologists postulate that much of Earth’s water came from melted cometary ice. Some biologists postulate that life on Earth arose from amino acids dumped by comets. Indeed, NASA’s Mission Stardust confirmed that comets possess amino acids when it returned with samples of amino acids from the tail of Comet Wild 2.

Rosetta, Philae are over 500 million km away, in the asteroid belt between Jupiter and Mars. A radio signal takes 28 minutes to travel one way from there to the European Space Agency (ESA), despite illusions of proximity caused by tweets from accounts run out of the ESA headquarters.

There have been massive technological advances in many areas of telemetry and material sciences, not to mention chip and solar panel design. A replication of the comet-hugging mission will be easier.

The mission originally intended to rendezvous with Comet 46P/Wirtanen. But the launch window was missed due to failure in the Ariane 5 launch rocket. Comet 67P/C-G is larger than 46P/W. That necessitated a hasty redesign of the landing gear.

All comets have notably eccentric orbits. In order to rendezvous with C67P/C-G, Rosetta had to swing out to over 800 million km away from the sun (about nine times the Earth-Sun distance) and then returned, to match orbit with C67P/C-G, which is travelling at over 65,000 km per hour. Rosetta was in “zombie mode” for 31 months with almost all systems in hibernation due to the lack of solar energy at extreme distance. Systems were woken up this January as Rosetta came back to about 670 million km away.

In August, Rosetta matched orbits with C67 P/C-G. It will accompany the comet through 2015. Perihelion (the closest approach to the sun) will occur on August 13, 2015 at a distance of about 185 million km. The comet will acquire its characteristic tail as it heats up.

Rosetta contains 11 scientific payloads. It has already made key discoveries about the comet, which is an irregularly shaped object of 4-km diameter, surrounded by the gaseous dusty atmosphere, known as the “coma”. Rosetta is expected to gather much more data in the next 13-14 months as it observes and records the comet’s journey to the sun and away.

Philae has 10 scientific payloads, deployed on the surface. Those have sufficient power for 64 hours operation. Solar panels will recharge batteries, allowing for about an hour of operation every 48 hours. Philae will have intermittent contact with Rosetta, which will monitor the situation and relay radio messages.

The gravity is less than a thousandth of the Earth. One fear is that the Lander will take off back into space. Philae was supposed to anchor by using harpoons and also supposed to fire a nitrogen gas thruster from its top to push it down at the comet’s surface. The harpoons and thruster did not work. The lander bounced twice, staying up once for at least an hour and a kilometre off the surface. The second bounce lasted about seven minutes.

Philae will send very high-res pictures. It will also run gas chromatography, alpha particle spectrography and stable isotope ratio analysis and so on to determine the composition of ices and organic material. It will also drill down and use radar to probe inside the comet.

Rosetta and Philae are named in honour of the 1820s deciphering of Egyptian hieroglyphics. The Rosetta Stone was found on Philae Island (now drowned by the Aswan Dam). It contained text written in Greek and Egyptian. The Orbiter-Lander combination could help decipher even more cryptic puzzles about the origin of life on Earth.

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