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.