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Emily LakdawallaOctober 27, 2014

A feast of comet features from Rosetta at Churyumov-Gerasimenko

I have been horribly behind in posting images from Rosetta's exploration of comet 67P/Churyumov-Gerasimenko, and that's a shame, because the spacecraft has lately been exploring the comet from a range of only 10 kilometers. From that range, the NavCam gets sub-meter resolution, and we're seeing a menagerie of odd surface features. Some of them are odd because I haven't seen anything like them anywhere else, like the crustily walled circular pits in this photo:

Comet Churyumov-Gerasimenko: pits, scarps, and boulders on the neck, October 18, 2014

ESA / Rosetta / NavCam / Damia Bouic

Comet Churyumov-Gerasimenko: pits, scarps, and boulders on the neck, October 18, 2014
The taken on 18 October from a distance of 9.9 km from the center of the comet, or about 7.9 kilometers from the surface, so the image covers an area about 1.4 kilometers wide. It contains a wide variety of remarkable landforms, including circular pits and scallop-shaped scarps, that result from weird comet surface modification processes.

Other features are odd because they look familiar and yet have no right being on a comet. I've called them "rhythmic ridges" in the caption to the image below, but to pretty much everyone who looks at them, they look like sand dunes. Which are just plain impossible on a body that has neither atmosphere nor much of any gravity.

Jagged comet landscape, October 24, 2014

ESA / Rosetta / NavCam / Damia Bouic

Jagged comet landscape, October 24, 2014
This four-image mosaic contains unusual rhythmic ridges and a jagged fissure, among other odd comet surface features. It was taken on October 24, 2014 from a distance of 9.8 kilometers from the center of the comet, or roughly 7.8 kilometers from the surface.

I called them "rhythmic ridges" because to call them dunes -- even if we all know that they couldn't have formed from wind or water saltating sand grains across a plain -- is to imply a cause. When you encounter unfamiliar worlds, it's all too easy to name things with terms that imply a cause and then fall into the linguistic trap that that sets up for you. It's how we got to seeing water in the "canali" on Mars. Of course, trying to avoid these pitfalls can give us really horrible names for geomorphic features, like the "recurring slope lineae" on Mars. "Canali" sounds so much more poetic.

Call them what you will, repeating ridges or "dunes" -- they show up in this gorgeous image, too. Also, I can't get over how well we can see into the shadowed areas with the light reflected off of the sunlit areas.

Comet jets from close range, October 18, 2014

ESA / Rosetta / NavCam / Damia Bouic

Comet jets from close range, October 18, 2014
Comet Churyumov-Gerasimenko puts on a show for Rosetta's NavCam in this photo taken on October 18, 2014. It includes rhythmic ridges on the comet's neck as well as small bright streaks that could be particles ejected from the comet, streaking across the Rosetta photo.

This view shows the comet in a different, softer mood. Views like this make you think the comet is covered with softly drifting snow; it's all too easy to forget that the surface of this comet is as dark as coal. Which is why I'm grateful to Claudia Mignone for explaining how a coal-black comet can look so bright and snowy in Rosetta photos.

NavCam view of comet Churyumov-Gerasimenko on October 15, 2014

NASA / JPL / Elisabetta Bonora & Marco Faccin

NavCam view of comet Churyumov-Gerasimenko on October 15, 2014
The four images for this mosaic were from a distance of 9.9 kilometers from the center of the comet, or only 7.9 kilometers from the surface. The view is across the small lobe to the large lobe. Image scale ranges from about 0.63 m/pixel on the part of the comet that is close to the viewer, to about 0.93m/pixel on the large lobe, farther from the viewer.

They released a couple of images from the OSIRIS science camera recently, all from the wide-angle camera, so we're not yet seeing to the teeny scales that the science team is enjoying. I love this long-exposure one that shows collimated jets erupting in all different directions. It was taken six weeks ago -- I know the comet is much more active than this now.

Comet Churyumov-Gerasimenko's jet activity on September 10, 2014

ESA / Rosetta / DLR / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

Comet Churyumov-Gerasimenko's jet activity on September 10, 2014
Rosetta OSIRIS wide-angle camera image of Comet 67P/Churyumov-Gerasimenko on 10 September 2014, showing jets of cometary activity along almost the entire body of the comet.

Here's a closeup OSIRIS image of more recent jet activity; you can slide back and forth between two different exposure settings, a short one to see surface features and a long one for jets and darker areas.

Before & after: Different exposure settings expose comet jets
Before & after: Different exposure settings expose comet jets

ESA / Rosetta / DLR / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

Before & after: Different exposure settings expose comet jets
Two views of comet 67P taken by the OSIRIS Wide-Angle Camera with different exposure settings reveal the surface (with an exposure of less than a second) and the jets (18.45-second exposure). Notice also the features in the shadowed areas of 67P that are lit by sunlight reflected off of sunlit surfaces. The two photos were taken on October 20, 2014.

I'm intrigued by the relatively bright-colored scarps along the neck in the shorter-exposure photo. They look like they might actually be a different color than the surrounding areas -- though it's hard to tell. It could just be a trick of the light. I cannot wait to see color images from OSIRIS. They've held all those close to the vest -- we may have to wait until the data get released to ESA's Planetary Science Archive to see them.

Finally, here is a photo that's not from the Rosetta team; it's work by space artist Michael Carroll, to give you a sense of the size of the comet. Enjoy this comparison of Churyumov-Gerasimenko and Mount Fuji. Thanks to Mikey's imagination, we get a sense of what the comet might look like in color:

Comet comparison

© Michael Carroll

Comet comparison
Rosetta's comet, 67P/Churyumov-Gerasimenko, compared to Japan's Mount Fuji.

The landing is in only two weeks, and I'll be in Darmstadt to report it! Stay tuned for news!

Read more: Rosetta and Philae, pretty pictures, comets, comet Churyumov-Gerasimenko

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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