Plucky little Philae

The remarkable achievement of landing on a comet

Something extraordinary happened over the last few days on an unimaginably distant, small hunk of rock named Comet 67P/ Churyumov-Gerasimenko, or 67P for short. A small machine, called the Philae lander, arrived on it. This is the culmination of a journey that is among the most epic in history. Philae was launched ten years ago from the European Space Agency's base in French Guiana. It had to travel across the solar system, to land on a precise spot, a few dozen metres across, on a comet 500 million kilometres away - more than three times the distance between Earth and its Sun. And, to top it all off, 67P happened to be travelling at a speed of 135,000 kilometres an hour at the time. This is not, of course, the furthest away that human devices have gone - the Voyager probes, launched as far back as 1977, are at the very edge of the solar system, and continue to send back data.

Comets, space's wanderers, are little understood. Their erratic paths have been studied, but their composition continues to be a mystery. Some are believed to contain trace elements that are of particular interest - some may even have the long carbon-linked molecules that are the building blocks of Earth's organic chemistry, giving rise to various theories about how comet collisions could have "seeded" Earth with life. Even if you discount such theories, there is much to be learned from comets' surfaces, and from their core - a tonne of information that can be translated, if you have the right key. That's why Philae is called Philae - a stone obelisk found at Philae in Egypt was one of the keys that helped modern historians decipher ancient Egyptian hieroglyphics. (The other was the Rosetta Stone, and the Philae lander is attached to the larger Rosetta spacecraft.) But getting on a comet is not easy. After launching, the Rosetta craft had to slingshot around the Sun several times to gather speed, and then had to turn its communications off for years, in order to conserve energy in the long dark run to 67P. When Rosetta turned itself on again earlier this year, the scientists who have spent their professional lives - entire decades - planning this must have rejoiced.

In some ways, one of the most remarkable things about the Philae lander is that it was launched and operated by the European Space Agency. A dozen European countries contributed technology and expertise to the Rosetta programme. The date that Philae approached 67P was probably a coincidence; but it came just as the nations of Europe were commemorating the 100th anniversary of World War I. A century on, Europe has forgotten the antagonisms and enmities that caused an entire generation to be wiped out. Instead, its countries are capable of collaborating to the degree that they can send the products of human ingenuity 500 million kilometres away, to dramatically extend the scope of human knowledge and science. Few things provide as concrete a sense of the progress of humanity as those two contrasting images.

Sadly, not all went according to plan. Philae's anchor thrusters failed to fire, and so it could not stay in the original landing place that was selected. Instead it bounced about and came to rest in a place where it did not get enough of the Sun's rays that it needed to survive - to keep on working and sending data to Rosetta. Almost all of the data Rosetta needed had already arrived, true. But, even so, the millions glued to the fate of Philae who rejoiced when it landed successfully felt a jolt of sadness hearing it was about to expire. That jolt was important. Something deep in the human spirit longs to explore, and the plucky little Philae lander was doing that, for everyone.