Photo of the Day

The craggy landscape of Comet 67P/Churyumov-Gerasimenko,
photographed by Rosetta's OSIRIS narrow-angle camera on August 3.
Rosetta is a spacecraft which is now traveling at 34,000mph alongside the comet, 60 miles distant, between the orbits of Mars and Jupiter, about 250 million miles from Earth—and the story of how it got there is pretty incredible:

Rosetta has flown a long way to get to this moment. It blasted off from Earth in March of 2004, and has followed a convoluted and looping path through the solar system before finally meeting up with the comet 10 years later. Along the way, it picked up three gravity assists from the Earth, one from Mars, and passed through the asteroid belt twice. All told, the spacecraft has flown 4 billion miles so far. And yet, in some ways, its work has just begun.

Other spacecraft have made comet flybys in the past, but a mere flyby is not what Rosetta is after. The ambitious mission first concocted in the 1970s and approved in 1993, entails not only escorting the comet along part of its orbit, but actually landing on it as well. To that end, Rosetta is carrying a lander called Philae that the ESA hopes to send down to the comet's surface in November.

"Arriving at the comet is really only just the beginning of an even bigger adventure, with greater challenges still to come as we learn how to operate in this unchartered environment, start to orbit and, eventually, land," said Sylvain Lodiot, ESA's Rosetta spacecraft operations manager in a statement.

The above photograph—about which Holger Sierks of the Max Planck Institute in Germany says, "We have never seen anything like this before in such detail."—is only the start of a mission that Sierks estimates will "revolutionize cometary science." Cool.