Philae successfully touched down on the comet

Today its lander Philae successfully touched down on the comet, using a harpoon or two to attach itself to the surface to avoid bouncing off into the vastness of space again. Rosetta is about the size of a minibus, with the two solar panels that power it each being about the length of four cars. Philae is about as big and heavy as a washing machine. The comet’s full name is 67P/Churyumov-Gerasimenko, named after the two Soviet scientists who discovered it in 1969 while analysing photographs from powerful Earth-based telescopes.
 The comet is about two and a half miles across, or the size of a small English village.
Over the next few days, Philae’s onboard robotic laboratory will conduct a number of experiments on the rock and ice nearby: the “artificial intelligence” required to do this is similar to that in domestic washing machines, where pressing one button can activate a complex series of actions.
 This Esa mission has cost almost £1bn ($1.58bn), and there has been some involvement by Nasa.
 As Esa says, the cost should be put into perspective: it is half that of a modern submarine, or the same as three of the latest Airbus jumbo jets, and has been spread over 20 years of scientific and industrial activity, creating thousands of jobs. Several British companies and universities have been involved in this cutting-edge project.
 But still, why should we spend so much money studying a large rock in space?
 First, and most importantly, we know that comets – and there are billions of them in the outer regions of our solar system – are debris left over from the formation of that solar system, between 4bn and 5bn years ago: they are frozen relics from a bygone age. Furthermore, there is evidence that millions of impacts by comets, composed of rock and ice, delivered enormous quantities of additional water to the inner planets. Only the Earth retained large amounts of water, of course. So studying the composition of comets significantly increases our understanding of the origins of our planet and our solar system. continue