Though NASA’s StarDust mission flew through the tail of comet Wild2 in 2004, no craft has ever orbited one. Rosetta will orbit its target at a leisurely walking pace, searching for a landing spot. Things will get even more exciting in November, when the robotic lander Philae (illustrated) detaches from the mother ship and becomes the first spacecraft to land on a comet.

Philae will anchor itself with a harpoon before starting to dig. An on-board lab will analyse the scoops of rock and beam the results to Earth. Like asteroids, comets are thought to preserve material from the birth of the solar system, 4.6 billion years ago. Comets contain water, so the chemistry of the scoops could reveal whether our oceans, and a bunch of molecules necessary for life, came from comets smashing into early Earth.