Bad Astronomy | A last good bye, again, from Rosetta

Just over a year ago, the Rosetta spacecraft performed its last act: setting itself down gently on the surface of a comet. It was the culmination of an adventure that launched in 2004 and began in earnest in 2014 when the spacecraft first approached the comet 67/P Churyumov-Gerasimenko.

For two years, the spacecraft orbited 67P, taking incredible photos and data that changed what we understood about these icy visitors. But all good things … on September 30, 2016, the mission came to end. Rosetta approached the comet, drawing ever nearer, snapping images on the way down. When it was 25 meters above the surface, just before touching down on the surface, it took one last image and sent it back to Earth.

… or did it?

Well, no. That was actually the penultimate image, the second-to-last shot. Rosetta actually took another one when it was just 19 meters (62 feet) above the surface. That image was in the process of being sent back to Earth when the spacecraft touched down on the comet and communication was cut off.

When the data got back here, the software that automatically processed it didn’t recognize it as an image, because only about half the data were transmitted. But almost a year later, engineers noticed the orphaned telemetry packets, realized what they had, and were able to reconstruct that truly last image from Rosetta!


This portrait of the comet’s surface shows an area about a meter across, with a resolution of about 2 millimeters per pixel. That means it barely resolves small pebbles. The part of the boomerang-shaped rock on the left we can see is about the size of, well, a decent boomerang (half a meter, or 18 inches, though part it is cut off on the left edge), and the rock next to it is about the size of an American football.

Due to the way the images were compressed and sent by the spacecraft, finer detail in the image was lost. But how’s this for attention to detail: In general, the OSIRIS camera on Rosetta was designed to take…

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