Dawn's first orbit, including RC3, March 6, 2015- June 15, 2015 Options

[MarsInMyLifetime]

Just to keep other causes in the discussion, we can't rule out some not-yet-obvious circumstance leading to secondary ejecta craters. But I do think the highly localized borders for some of these pits does speak to flows rather than ejecta. And other volatile materials than water could be at work as well. The Sander Crater example is similar only by possible mechanism; the soluble material there may have had a much higher temperature of sublimation/vaporization than water. In fact, I've seen solder blobs that pulled into such shapes; other volatile materials had nothing to do with the puddling behavior of the melted material.

[Habukaz]

Yep, the bright spot is in the latest navigation images (OpNav 8). Image quality is pretty poor, though.

[Gerald]

For convenience, the bright spot 8-fold magnified, and brightness-stretched in a nonlinear way, darker parts mapped to black:

[elakdawalla]

Personally I'm more than happy to accept lots of JPEG compression artifacts in exchange for relatively quick release of new images. So far Ceres has been so much better than Vesta in terms of image release.

[Steve G]

We are finally at the point where we can't get all of Ceres in a single frame, so quality is amazing! It wasn't that long ago were were stretching to death 20 pixel wide images.

[Gladstoner]

It's puzzling, though, that the associated TIF images have the same JPG artifacts. One would think they would use unaltered images for the ~1-meg files.

[JRehling]

I thought I'd inject a comparison between Ceres' bright spots and albedo patterns that we've seen up-close on Phobos. Eg,
http://photojournal.jpl.nasa.gov/catalog/PIA10368

Phobos is of comparable distance from the Sun, and is also dark with bright spots. We can see that the bright areas underlie the dark surface and are exposed by combinations of impact cratering and downslope flow. We also see that craters within craters can create arbitrarily fine detail. We also see asymmetries that might not, a priori, be expected: Bright spots at certain places on a rim, but not in others, and bright patches where two causes of incline add (e.g., the upslope wall of a crater within Stickney), but no bright patches where two causes of incline cancel out (the other side of that crater within Stickney).

Overall, there is a simple layering of dark over light, and physical exposure of the ice happens for two simple reasons (impact and downslope mass movement), with anisotropies in topography causing boundaries that appear complex.

This seems like a prominent model to consider for Ceres' bright spots until better observations show the nuances of the bright spot boundaries.

[volcanopele]

It's puzzling, though, that the associated TIF images have the same JPG artifacts. One would think they would use unaltered images for the ~1-meg files.

It's possible that they were returned as lossy-compressed images. These were opnavs after all, needed more for navigation than for science, so fine surface details aren't as important as seeing where the limb is. I know with Cassini we have the option to use that or lossless compression. I always use lossless compression because Titan's atmosphere makes my data blurry enough...

[Gladstoner]

It's possible that they were returned as lossy-compressed images. These were opnavs after all, needed more for navigation than for science, so fine surface details aren't as important as seeing where the limb is. I know with Cassini we have the option to use that or lossless compression. I always use lossless compression because Titan's atmosphere makes my data blurry enough...

I thought that might be the case, but the images in the recent animated GIF appear to be unaltered, while images selected from the same sequence and released in TIF and JPG format are degraded. A comparison, from left to right, are GIF (movie frame), TIF, and JPG:



I'm grateful they released that movie in the original quality.

[elakdawalla]

It's horrible but true that the TIF versions of images at Photojournal are sometimes made from JPEG originals. It was probably provided to JPL by the FC team as a JPEG. Now, JPL could have just grabbed a still frame from the animation and posted that instead, but on missions there are agreements about different organizations having to post the same images at the same time, so it's not something they would ordinarily do.

[Habukaz]

It's possible that they were returned as lossy-compressed images. These were opnavs after all, needed more for navigation than for science, so fine surface details aren't as important as seeing where the limb is. I know with Cassini we have the option to use that or lossless compression. I always use lossless compression because Titan's atmosphere makes my data blurry enough...

I asked about that, and it seems that the answer is no:

Most of the compression artifacts you are seeing are the result of the conversion from raw data to JPEG format

https://twitter.com/NASA_Dawn/status/601070407094009856

[charborob]

While converting to JPEG, why didn't they specify "maximum quality"?

[scalbers]

A simple map with a bright spot image projected onto the previously released map.

[Gladstoner]

This crater floor fracture shows a little more detail in the new release:

[ngunn]

I thought I'd inject a comparison between Ceres' bright spots and albedo patterns that we've seen up-close on Phobos

Excellent analysis (as ususal) but I'd be surprised if the bright material on the surface of Phobos was ice, so is it salt? If so that gets us somewhere.