Conquer Club

Rosetta’s lander 100kg Philae will target Site J, an intriguing region on Comet 67P/Churyumov–Gerasimenko that offers unique scientific potential, with hints of activity nearby, and minimum risk to the lander compared to the other candidate sites.

Site J is on the ‘head’ of the comet, an irregular shaped world that is just over 4 km across at its widest point. The decision to select Site J as the primary site was unanimous.

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The gravity of the comet is 60,000 times less than the gravity of Earth, and scientists expect it will take the lander seven hours to free-fall from its mother ship, Rosetta, to the comet. Then there is a delay of 28 minutes for a signal from Rosetta to reach our planet.

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O'Rourke (operations coordinator) says there's lots of risks and puts their chances of success at about 70%. "You have to face reality," he said. This was the best of the five possible landing sites -- we've got what the comet has given us. It's the best of the worst. There's craters, crevices, boulders, gravelly areas. It [Philae] could tip over. The comet is a very strange structure and there's a lot of luck involved," he said.

The comet's gravity is so weak that there's also a danger that Philae could bounce off so it has been designed to grip on like a limpet. O'Rourke explained that at touchdown, harpoons from two of the three feet fire into the surface and the attached cords rewind to help anchor the craft. A thruster on top of the probe fires to push down the probe, and screws on each foot bore into the surface -- all within 15 seconds of landing.