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The Bright Spots on Ceres
David Palmer
post Apr 7 2015, 10:00 AM
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QUOTE (elakdawalla @ Apr 6 2015, 03:18 PM) *
Oh, that's a very good point that I had forgotten to consider and is obvious in retrospect smile.gif We don't have enough data yet to know the actual shape of the crater floor or the height of the rim with respect to it. We'll have to wait and see the stereo data.


On the basis of that consideration, it sounds like the spring mound I was arguing for, will likely not need to be nearly as high. However it seems we can still rule out anything but a positive-relief feature, as a crater or sinkhole or other negative-relief feature (exposing clean subsurface ice) would disappear when seen edge-on near the limb of Ceres.
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dudley
post Apr 10 2015, 06:19 PM
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According to the published schedule, Dawn should be making images of Ceres today. If past experience is any indication, we may hope to see these by the 15th or 16th. Planned images, taken on the 14th should probably be released by the 19th or 20th. Given current uncertainties about Ceres' period of rotation, the bright spots may, or may not be visible in these images.
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Habukaz
post Apr 10 2015, 06:26 PM
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The images being downlinked now will not show the brightest spots. The next OpNav might.

Edit: I see your post might be interpreted that way.


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Gerald
post Apr 10 2015, 07:54 PM
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QUOTE (David Palmer @ Apr 7 2015, 11:00 AM) *
On the basis of that consideration, it sounds like the spring mound I was arguing for, will likely not need to be nearly as high. However it seems we can still rule out anything but a positive-relief feature, as a crater or sinkhole or other negative-relief feature (exposing clean subsurface ice) would disappear when seen edge-on near the limb of Ceres.

In the other thread I've posted reprojections of some of the RC2 sequence in order to show the bright spot at almost the same position.
Comparing the visibility of the bright spot relative to the surrounding crater with other craters / crater rims / craters in craters when near the terminator, I can't perceive hints to a particularly high peak related to the bright spot.
I'm curious what we'll learn from the new sequence.
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JohnVV
post Apr 11 2015, 10:36 PM
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-- better here
-----------------------
if the rotation of Ceres is close to correct then in the next few days we should start to see the bright spot
( i am using the "dawn_ceres_v02.tpc")
the times are in UT in the screenshots
upper left on the limb

visible on the top
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David Palmer
post Apr 12 2015, 12:41 PM
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QUOTE (Gerald @ Apr 10 2015, 11:54 AM) *
In the other thread I've posted reprojections of some of the RC2 sequence in order to show the bright spot at almost the same position.
Comparing the visibility of the bright spot relative to the surrounding crater with other craters / crater rims / craters in craters when near the terminator, I can't perceive hints to a particularly high peak related to the bright spot.
I'm curious what we'll learn from the new sequence.


Since the bright spots are unresolved in the pictures so far released, and thus appear to be less than one pixel wide, it seems unlikely that any associated topographic peak (or mound) would show up in such photos or projections based on them.
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JohnVV
post Apr 12 2015, 06:55 PM
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to make matters worse
the gif that was released is a 8 bit indexed normalized 5% to 95 % image
almost 100% useless for most things

good for the angle triangulation done earlier ( the rim of approx. 2.5 KM )
but that is about it

now if the 12 bit raw data ( basically the pds img ) was around ??????
(or is the CCD 16 bit ?)
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Habukaz
post Apr 13 2015, 02:26 PM
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One theory (prominent?) among the researchers is that the brightest spot is located in a depression, not elevated over the surrounding terrain:

QUOTE
"It appears there are shadows crossing the reflecting region earlier than would be the case if it were a smooth region at the level of the material around it. So, the thought is right now - without having the resolution we really want - that there is a depression there, rather than a mound," he told BBC News.

"It's not a little mountain of bright material, but it might be some bright material in a pit, or something of that nature."


(Chris Russell)

http://www.bbc.com/news/science-environment-32290122


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dudley
post Apr 13 2015, 08:18 PM
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The newly released images use the VIR data to compare the temperatures of two different bright areas on Ceres. Area 5 is the much discussed double bright spot. Area 1 is another, smaller appearing and somewhat less visually brilliant bright spot.

Area 1 seems to be cooler than its surroundings, appearing as dark and prominent in the thermal infrared, just as might be expected of an area that is light colored in the visual range. Area 5 essentially disappears in the thermal infrared range. No temperature difference from its surroundings is apparent.
Since Area 1 is smaller than Area 5 it is presumably even less well resolved optically, less distinguishable from its surroundings than is Area 5. Even so, it was possible to find a lower temperature in Area 1 than the area around it. It seems that it should have been possible to do the same for Area 5.
Since Area 5 does not appear to be cooler than its surroundings, there is a question we must ask. What is there about this light colored area that prevents it, in common with other light colored surfaces, from reflecting enough solar energy to lose a greater amount of heat than a darker surface?
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Gerald
post Apr 14 2015, 05:03 PM
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QUOTE (David Palmer @ Apr 12 2015, 01:41 PM) *
Since the bright spots are unresolved in the pictures so far released, and thus appear to be less than one pixel wide, it seems unlikely that any associated topographic peak (or mound) would show up in such photos or projections based on them.

... so there is no evidence for a peak from the images.
At other locations there is evidence. To make it more feasible, here a montage made from three reprojected single images:
Attached Image

Compare the distances of last visibility of a presumed peak/rim to the terminator.
The distance of the bright spot to the terminator in frame06 is about the same as the rim in frame08. The bright spot is already in the shadow under otherwise similar conditions where the rim is still visible.
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