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Crater relaxation (and volatile transport?) on Ceres
Explorer1
post Oct 30 2015, 02:04 AM
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That image is 27 meters per pixel, according to the original caption (http://saturn.jpl.nasa.gov/photos/imagedet...fm?imageId=4662)
I was thinking of Methone in the discussion above too, but this is clearly a very different object from Ceres! There's more than one way to erase craters, even in a vacuum.

Fun fact, the little fellow orbits Saturn in almost exactly one Earth day, so the surface experiences pretty much the same cycle we do since it's tidally locked; just a odd coincidence of course...
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MichaelPoole
post Oct 30 2015, 01:15 PM
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That may seem like a good resolution for other objects, but bear in mind this moon is just 1.6 km across - so the real resolution of this image is just about 59 pixels wide.

To compare, Itokawa was pictured at a resolution up to 70 cm per pixel.
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Herobrine
post Oct 30 2015, 08:00 PM
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QUOTE (MichaelPoole @ Oct 29 2015, 08:46 PM) *
I think that's less "polished ball of ice" than "dusty rubble pile that seems smooth because the photo is low-res and taken from a big distance".

I don't think it's a lack of resolution that makes it seem so smooth. The surface is fairly well-resolved. Looking at the limb gives you a good sense of how much detail is provided in the image. It's only a few kilometers across, but according to http://www.planetary.org/blogs/emily-lakda...2/05211206.html, that image was captured from a distance of less than 5,000 km by Cassini's narrow-angle camera (angular resolution: 0.00006 radians). http://www.lpi.usra.edu/meetings/lpsc2013/pdf/1598.pdf says the image has a resolution of 27 meters/pixel, and still shows no visible topography. Both of those sources agree that the surface of Methone is remarkably smooth, with Thomas et al. adding that it and Pallene "have likely developed shapes close to equipotential surfaces".
It may still be a "dusty rubble pile"—its extremely low density estimate supports that—but it must be a very smooth one.
To merge several sources' descriptive terms, 'icy fluff ball' seems appropriate.

Edit: Oh, we've spilled over into page 2. Some of what I just wrote is redundant after reading the posts I missed.
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MichaelPoole
post Oct 30 2015, 10:21 PM
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Man, Methone is not a few km across. It is just 1.6 km across. That resolution is insufficient to see really fine detail on something so small.
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ngunn
post Oct 30 2015, 10:40 PM
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Meanwhile, back on Ceres . . .
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Explorer1
post Oct 31 2015, 01:47 AM
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Yep; back on topic, this month's journal is out: http://www.planetary.org/blogs/guest-blogs...ty-of-data.html
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