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

[scalbers]

Yes I tend to agree thinking its resolved or nearly so on the first image of the sequence, but on the subsequent images it seem to get saturated and float into adjacent pixel areas -and so larger than it actually is -again

The linear arrangement almost has the look of the "Voyager Mountains" on Iapetus...

[ZLD]

Performed some slight enhancements on frame 10 of the PIA19064 animation. Cropped, luminance adjustment, deconvolution and scaled 200%.


And again with frame 11.


These are stretched until the bright region is slightly below max saturation.

[Gladstoner]

The bright spot seems to be less prominent when on the morning terminator than on the evening. One possibility is that much of the bright material is on a west-facing slope.

[dudley]

Dr. Chris Russell, principal investigator of the Dawn mission, indicated in an e mail today to NBC News that even at the current resolution (1300 2100 meters/pixel) the bright spots were not resolved. This will presumably necessitate a marked revision upward of the albedo of the spots, which was set a minimum of 40 percent, based on the previous resolution of 3.7 kilometers/pixel.
NBC News Article

[Explorer1]

The fact that these things were visible from Earth still blows my mind. How small would they have to be before we get in the range of an Enceladean albedo?

[Gerald]

Assuming the globes

here a forward/back animation (1200 pixels) of rectangular roughly map-projected versions of the 20-frames OpNav7 sequence PIA19064.gif, aligned to the DLR RC2 map:

(NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/"Gerald")

Album of individual projected frames (1440x720 pixels).

[dudley]

The fact that these things were visible from Earth still blows my mind. How small would they have to be before we get in the range of an Enceladean albedo?

Well, it appears that the ratio of an area 3.7 kilometers in diameter to one that is 1.3 km across is about 8.1 to 1. I'm assuming that albedo is inversely proportional to reflective area. If I'm not mistaken, one could multiply the old albedo figure of 0.4 by the 8.1 ratio to get the minimum new albedo.

[Gerald]

Albedos greater than 1.0 are very rare in nature.

... Forth-back animation of polar projections of OpNav7 (same globes assumed as above) :


Album of individual 1440px maps.

[alk3997]

The bright spot seems to be less prominent when on the morning terminator than on the evening. One possibility is that much of the bright material is on a west-facing slope.

If this were a geologically recent active region, wouldn't a reasonable expectation be that the crater floor is smooth as the material flows or falls onto the floor? It's hard to tell whether the crater floor in the zoomed-in version is itself cratered or those are image processing artifacts.

My money is still on a shallow angle impact causing the center bright spot with a secondary impact causing the second spot. It also explains the variability in brightness between different viewing angles.

Andy

[fredk]

Dr. Chris Russell, principal investigator of the Dawn mission, indicated in an e mail today to NBC News that even at the current resolution (1300 meters/pixel) the bright spots were not resolved.

It probably depends on exactly what you mean by "resolved". There's certainly not much detail visible in both of the two spot 5 subspots, but I would call them "resolved" in the sense that they are clearly larger than the PSF. Both of the subspots are elongated, and the orienation of elongation rotates with Ceres. This means the elongation can't be due to bad optics (eg, astigmatism) and almost certainly not due to motion blur during the exposure. Similarly, it is extremely unlikely for pixel noise to conspire to produce elongation in both subspots rotating consistently with Ceres's rotation, even though we're looking at only a small number of pixels here (ie, S/N looks good judging from frame-to-frame consistency).

It appears that the fainter subspot (upper in my animation below) is composed of two "sub-subspots" (again, the consistency from frame to frame argues against pixel noise). The brightest subspot (lower in my animation) perhaps also consists of two sub-subspots, the lower of which appears first and the upper which brightens. As others have pointed out, these sorts of brightness variations could be simply due to variable geometry of exposed surfaces/shadowing.

[Gerald]

I'd assign the apparent split of the fainter spot to a more or less concentrical topographical feature in the crater. So it's not necessarily an albedo feature, but possibly an "inclination" feature.

[fredk]

But the upper double spot only brightens as you go from frame to frame. If the dark gap between the two sub-subspots was due to inclination, the dark gap should have been more prominent in the earlier frames when the illumination angle was lower.

Of course the real problem is that we're arguing over only a few pixels here. One way to improve things while we wait is to note that the spot 5 crater remains at roughly the same distance from the limb in all the frames, ie we're roughly "looking straight down at the north pole". So the viewing geometry for the crater is roughly constant. So someone could usefully do a poor-man's superresolution by enlarging (say 4x), rotating, and then stacking the images...

[dudley]

It probably depends on exactly what you mean by "resolved". There's certainly not much detail visible in both of the two spot 5 subspots, but I would call them "resolved" in the sense that they are clearly larger than the PSF.

I recall when only one bright spot was discernible in this crater, then there were two. There was apparently no claim that the spot had been optically resolved at this point. When Dr. Russell says that the spots are not resolved because they're too small, I'm inclined to rely on that, given his expertise, and knowledge of this particular situation.
It does not appear to me that the brighter of the two spots is even separated into two distinct parts, which seems to argue against any reasonable definition of the word 'resolved'. The variable lighting of portions of this spot could have any one of several explanations. The bright spot sometimes appeared to be elongated in the images, long before there was any thought that it might be optically resolved.

ADMIN NOTE: Everyone - I think that we can drop the discussion over the word 'resolved'. You can go into the 'micron' scale and still not fully "resolve" an object. Let's just wait for better images that will help to identify the nature of these features. Not long now.

[JohnVV]

The bright spot seems to be less prominent when on the morning terminator than on the evening. One possibility is that much of the bright material is on a west-facing slope.

as one can see in the second attached image in post # 41


it is on a west facing slope


as to the other one
WE WELL SEE --- once there are better images

[dvandorn]

In the previous image, and also in the animations showing this region, I'm tempted to say that it's not ejecta that's so bright. This "spot" is resolved to the point that, when not saturating the ccd's, it looks like a pyramidal structure (in shape, not at all suggesting it was artificially constructed) that is definitely lighter in color than the surrounding terrain. It doesn't exactly follow the curves of the crater wall it seems to overly, either.

I'm wondering if this could be a constructional landform -- looks a little like a volcano-like structure in this image, at any rate.

Boy, it'll be nice to get better pictures of these areas. Patience... I must learn patience...

-the other Doug