It’s a stunning view. And as the imagers and instruments on our spacecrafts keep improving, so will our understanding of the Heavens. And the Earth.
The illuminated section is our South Pole, with the rest of the Earth so dark you can’t discern it from the emptiness that surrounds us.
If you’re wondering whether the crescent is waxing or waning, it’s waxing. The motion of the spacecraft that took this picture — Rosetta — was bringing it closer to the Earth for a gravity assist to fling it outwards into our solar system for a rendezvous with comet 67P/Churyumov-Gerasimenko in 2014. The successful swingby increased its speed from 13.3 km/sec to 16.9 km/sec. In comparison, the space station maintains a speed of only 8 km/sec — or Mach 23. So yeah, Rosetta is moving! To get up to this amazing speed the spacecraft used the momentum of four planetary flybys, three of Earth and one of Mars.
Here’s the sequence of photos it took leading up to that beautiful one plastered on every science website in the blogosphere. Each image in this animation was taken only one hour apart!
Rosetta is on a mission to catch up with a comet and then set a lander on its surface! Since the comet is only 4km in diameter, it won’t have enough gravity to hold the lander to it; so the ESA plans to harpoon this white whale and ride on its back a while. How long of a while? That depends on how long it takes the comet to tear it apart. Since this comet isn’t under thermal stress atm, it might survive for years — which is quite a different story than when Halley’s comet beat up an ESA probe named Giotto in a matter of minutes back in 1986. That mission was uniquely different. The comet Rosetta is headed for won’t be shedding material; Giotto encountered Halley’s comet right after it passed the sun and had a tail a million miles long! I remember when they launched it, way too late for a good look, kinda thrown together at the last minute sort of thing. (I say that. Of course, you know the whole operation was ran by some really smart engineers and was very well planned under the circumstances.) It was outfitted with instruments and then flung toward the sun to pick up some terrific speed. It then headed *toward* comet Halley in a nearly perpendicular direction that would have them passing each other at 68 km/sec! As you can probably guess, this didn’t end well. As it approached, the Giotto got pelted some 12,000 times by little ice chunks. The antenna was hit, the aluminum and Kevlar shielding was demolished, and an impact with a “large” chuck with the mass of a paperclip (hey, it’s going really fast, ‘k?) sent it spinning out of control. There is a happy ending to this tale, though. A half-hour after it was knocked silly it re-stabilized itself and went on to produce good science for another 7 years — even making an unprecedented encounter with a *second* comet.
So now Rosetta is off to rendezvous with it’s own chunk of primordial ice. The ESA will try to tell you of all the important science the probe should be able to do, but I think we all know why it’s really going… ’cause we all want to see what the surface of a comet really looks like! I bet it’s cooler than we’ve ever imagined.