The mysterious white stuff

The spacecraft Dawn has gotten a closer look at the mysterious white spots on the asteroid Ceres.  In the first photos, they were so bright they were overexposed!

Now Dawn is closer.   Here's the biggest patch of white stuff, called Spot 5, in a crater called Occator

What is it?   The obvious guess is some sort of ice or salt, reflecting sunlight.  But here's the cool part: you can sometimes see haze  over Spot 5.   This suggests that some sort of gas is coming up from beneath the surface!  Or maybe the ice is sublimating, turning into vapor... perhaps explosively?

The mission director writes:

"Dawn has transformed what was so recently a few bright dots into a complex and beautiful, gleaming landscape. Soon, the scientific analysis will reveal the geological and chemical nature of this mysterious and mesmerizing extraterrestrial scenery."

This picture is a composite of two images: one using a short exposure that captures the detail in the bright spots, and one where the background surface is captured at normal exposure.  Each pixel here is a 140 meter × 140 meter square.

Right now Dawn is orbiting Ceres at a distance of 1450 kilometers.  In December, it will descend to just 375 kilometers from the surface.  Then we'll get even better images! 

And when the mission ends?  Then Dawn will remain as a permanent satellite of Ceres.  A fitting end to a great mission - it's the first spacecraft to orbit two bodies, Vesta and Ceres.

You can watch a short video of what Dawn has been seeing, here:

https://www.nasa.gov/jpl/dawn/cruise-over-ceres-in-new-video

This image came from here:

http://www.nasa.gov/feature/jpl/ceres-bright-spots-seen-in-striking-new-detail

For more on the haze, read this:

http://www.nature.com/news/mystery-haze-appears-above-ceres-s-bright-spots-1.18032

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