I'm finding these greater-than-Hubble resolution numbers really interesting in light of the extremely large telescopes we have under construction, which will have somewhere from 8 to 15 times HST's resolution. Here at 7x Hubble we're still not at a point that could be described as satisfying, given that what the white spot is is still speculation. April 15th at 21,000 km is when we will have 15x resolution, which is what the European Extremely Large Telescope (completion in 2021) is supposed to have. So if we're still not satisfied with what we can see of the white spot by then, starting in the 2020s maybe we're going to start seeing quite a few detailed yet maddeningly inconclusive asteroid belt images. Pallas, Themis, etc.

Someone on Reddit has also put these together:

http://i.imgur.com/5UPx6lz.png

Nothing new but it shows the constant improvement of Dawn's images from the 1.5 million km mark until now.

While we are speculating...(and perhaps stating the baseline least fun option)

Maybe the double white spots are just a low angle impact (that just cleared the rim of the crater) with a hop like Messier and Messier A on the moon exposing some ice?

...or an impact of small asteroid or comet with a moon

Click to view attachment

I recall that there were several predictions of a "soft" surface due to high enough temperatures that the ice crust should be, to a certain extent, elastic -- certainly more elastic than a fully rocky crust.

I think we're beginning to see that. A lot of the larger, basin-sized features look like their floors have either been almost fully filled in or -- as would have been predicted by the elastic crust theory -- have completed an isostatic rebound and have re-conformed to a spherical surface. That would be a possible indicator of the ages of large crater events; older craters have rebounded more than newer ones.

Perhaps one of the secondary aspects of this kind of rebound would be the movement of fresh "soft" ice beneath the cratering event, which would result in a slow extrusion of brighter ices through weak points, like central peak formations. Hence the bright spots seen, in some places, near the centers of large craters. Including the CWS.

I've seen a lot of what look to be examples of the "rebounded-floor" craters and basins thus far, especially on the most recent images. I'm looking forward to seeing more and better examples as we get closer and closer...

After staring at it for awhile, I'm starting to wonder if 2 bright features is still an underestimation... If I squint I can imagine as many as 6 or 7 (see attached, 4x [more] bicubic + levels adjust).

If (if!) they are craters, they don't appear to nicely line up as in a typical crater chain, which could suggest that they are not actually related to one another. Perhaps the ice is just unusually close to the surface here (and/or more pure, as ngunn suggests), such that any new impact in this crater will produce a shiny new spot. But still - what's special about this crater? We just won't know until we get some images that aren't saturated.

And there really does seem to be a diffuse albedo feature surrounding the spots - like others I would love for this to be evidence of activity but ejecta seems more likely.

Click to view attachment

That big ancient basin (and several others) sure look completely relaxed ice moon style. And it has a mountain inside it which must be relatively young. Also (and I know that we need a closer look), there seems to be a scarcity of medium to small craters. Ancient impact terrain clearly hasn't been erased to palimpsests as was predicted by a few papers, but neither is this just a pummeled, primal landscape. The big basin to the south of 'white spot crater' seems to have a darker, mare like flood on its floor. Other areas seem mare like too. Fun!

P

My hypothesis for an ice pack on a hot spot inside a caldera is weakening but the hot spot hypothesis keeps on track.

The edges of the craters appear relatively smooth and the craters are not particularly deep. I guess that the mean density of the crust is relatively low and that the concentrations of water ice, ammonia ice or frozen carbon dioxide are significant. We'll see!

The contrast between the two bright patches and the rest of the surface is really surprising.

If the bright patches are related to a hot spot, how can we explain the energy source since there are no tidal forces related to neighboring bodies like for Enceladus, Triton, Io or Europa ?

Excellent image!. I enhanced it with an unsharp mask and added some arrows pointing to the boundaries of multiple episodes of resurfacing, south and west of Searchlight crater (for want of a better name). There are meandering double lines west of the crater and the most recent flow front partially covers a crater immediately to its south. The large basin at bottom may have triggered that event.
Click to view attachment

In the OpNav 3 images, the bright spot looked like it was sitting right at the edge of a dark area. Where did that dark area go? The RC1 images would have been really helpful here.




The dark area did look kind of weak (not that evenly dark), though; so perhaps I sholdn't be surprised. Although there does actually appear to be some darker surface materials below the crater in the crop above.

I think the 'dark area' lies just outside the newly resolved crater to the upper right. It was probably a slope effect.

A first attempt of map projections based on Volcanopele's version of PIA19185.
The globes need some more adjustment to the distortions:
Click to view attachment
Rectangular lon/lat projections based on these not yet quite fitting globes:
Click to view attachment Click to view attachment Click to view attachment
And just taking the brightest of the projections to compare it with previous maps:
Click to view attachment

Edit: I get a slightly better match with diameter assumptions pole to pole / equator = 920/975. Not clear, whether that's real or due to processing.

Perhaps the white spot is where the Iron Chicken landed, if so, there could be Music Trees nearby. lol.

Speculating - I have to agree with Ken2 that a shallow impact is a possible source. The first impact uncovered ice in the "middle" of the crater (and made the crater) while a secondary impact uncovered ice on a ridge to the east which just barely appears in the photo. I suppose it could be material coming up from the interior but uncovered ice seems more likely.

As far as number of bright spots, if I've read correctly, the spots are still not full resolved in the latest images. So we don't know how big the spots are yet, let alone how many there are. The smaller the spots the higher the albedo will be. But, we don't know that yet.

Andy

I think we have to be cautious about interpreting features in extreme zooms like 16x. (I was already uncomfortable about going to 4x, but at least the S/N seems to be very good and 4x matches the first two release images.) If you look at the original image trivially resampled 16x you can see that some of the bright spots you circled correspond to pixels in the original image:
Click to view attachment
Any single-pixel feature could easily be noise (although S/N looks quite good).

Anyway, my 16x image here appears to show that the main bright spot spans at least 2x2 pixels, with a more diffuse region out to at least 3x3 pixels, and hence may actually be (just) resolved. I say "may" because I don't know what the PSF is like for this camera, ie if they imaged a star, how many pixels would it span?

Finally, I don't think anyone has mentioned that we can now see clear departures from an ellipsoidal global shape along the rim, eg:
Click to view attachment
The departures are on the order of several pixels, ie several kms, which presumably tells you something about the structural strength...

Echoing what Fred said, I don't trust the existence of any "feature" that is less than 3 pixels in size -- in the original images, not the enlarged ones. Many of the images being released are first enlarged, sometimes by as much as a factor of 10, and and then sharpened. Sharpening can create brightness contrasts where none existed before -- for instance, it makes the limb appear especially bright. Sharpening could have caused the dark feature next to the bright feature in earlier releases.

According to this calibration document, the PSF is 1.0-1.6 pixels at FWHM, depending on the filter in use. However, accoding to my non-expert reading of the document, it also says that when testing this with real stars, the actual response of a given pixel to a point source depends on the horizontal position of the source on a pixel, because anti-blooming gates run vertically on the CCD. reducing fill factor (though this is less of an issue for long exposures because of pointing drift).

So I think this implies that 1x1 pixel is possible but not always going to happen for a point source. But it would rarely exceed 2x2 pixels, unless a really long exposure. And for short exposures, unless stacking multiple dithered images, a <<1 pixel point-like source could show inconsistent brightness.

EDIT: and per Emily's note, this is of course all for raw images, not the web-released rescaled JPGs.

Additional edit: I also found the below table in the preview of the book The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres. It uses a slifhtly different definition and gives PSFs for each filter, slightly larger than the FWHM metric above.

Click to view attachment

This map is a composite of Gerald's new reprojections and the previous map with a couple of Rotation 1 images.

The black area at the south pole is an error in the older reprojections. The south pole should be pretty much on the terminator, so visible detail in the older images should extend to the pole. Gerald misaligned the image with the grid (sorry, Gerald!) so dark space beyond the pole appeared to be on the disk. Similarly with these new projections, the north pole should be pretty much on the terminator, but two of the three reprojections put the pole well on the disk, hence the strip of visible surface all the way across the top.

Despite this, the composite shows the distribution of major features fairly well now.

Phil

Click to view attachment

We should also remember that the PSF need not be a Gaussian or even symmetric (see the New Horizon teardrop-shaped PSF, as I recall). And even if the FWHMPSF is 1 pixel, about half the light falls outside that pixel. So a point source centered on a pixel should make a ~3x3 image with the central pixel much brighter than the rest. But, if the PSF is non-Gaussian, it would be easy to make, for example, a 3x3 PSF with 4 fairly bright pixels in a rectangle.

My ex-astronomer opinion is that JPL (and we!) are torturing these images to the extent that all we can say is the white spot is barely resolved, if at all. We can't really estimate albedo and such because we don't know the stretch of the posted images.

Has anyone estimated the minimum albedo of the most prominent bright spot?

I will add here that it still really looks like Umbriel. Unfortunately, the best image of Umbriel we have, on the right, has now been surpassed.
Click to view attachment

Agreed. But even if the PSF is close to Gaussian, if the central pixels are overexposed (clipped), you may be raising the tails of the Gaussian and end up with a broader distribution than the actual optical PSF. So again, there's not much we can say without the raw images and probably without better resolution.

We may even need a shorter exposure to avoid saturation.

Just a better visualization of my previous post hypothesis - the crater slope allows for an extremely low angle of impact which could cause a trough and a hop and a final bigger crater - see image with superimposed lunar Messier crater comparison (scaled smaller). Even better it looks like the wall of the crater has been previously knocked down in the impact direction even allowing for a shallower impact.

Click to view attachment

Is it confirmed that the central pixel is clipped, then? That's very interesting indeed if true, but JPL may have just stretched the image such that the highest DN pixel was white, no?

Dumb question. Could Ceres be an ice giant's moon scattered into the inner solar system by a huge disruptive event like:
1) The putative Uranus tilting impact
2) The capture of Triton from the Kuiper belt

Or would these type events tend to scatter moons out of the system altogether?

p

I remembered hearing about the possibility of Ceres migrating from the Kuiper Belt.

Here is a reference (with abstract) to a paper discussing the possility:

http://adsabs.harvard.edu/abs/2008DPS....40.3803M

"Or would these type events tend to scatter moons out of the system altogether?"
Each scenario from falling into the Sun, colliding with other objects, changing orbits, establishing a resonant orbit with another object, capture, ejection from the solar system is possible, depends on the initial conditions, although not equally likely.
Usually objects return to near the position of the orbit-changing close encounter. Since there is no big object/planet orbit crossing Ceres' orbit, such an encounter in the past is less likely, although the other object might have had another close encounter or collision, such that the history is obscured by now. Or by the gravity of Jupiter the orbits changed gradually making it difficult to track the orbits back into far history.


Here is an album providing several series of files within these constraints assuming 87% illumination.
The *m15.png series fits best with an ellipsoid (see file PIA19185_volcanopele_wider2_32bit_withGlobe3_termRot_m15.png).
Thus far I didn't find convincing matches within a triple of reprojections to fully pin down the parameters.
If someone likes to have a try while I'll need a small break...

Files are derived from NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/"volcanopele".

Interestingly, there appears to be quite a bit of variation in landforms in this image:

Click to view attachment

The area circled in green appears to be ancient terrain with saturation cratering.

The area circled in red is somewhat rough, but there is a paucity of craters (except for the two large ones). Furthermore, the basin near the left limb has a noticeably modified rim, assuming it is an impact structure. Perhaps the area is just an ejecta blanket from a large, still-unseen basin, but it's fun to think about other possibilities.

Does no-one like my Icy moon impact debris fragment impact proposition?

Just to be clear, a standard rocky body or iron fragment hits an icy moon, e.g. Europa, debris from the surface of Europa flies into space, possibly on it's first trip to the inner solar system, or possibly never traveling closer to the Sun than the vicinity of Ceres orbit, otherwise it would be evaporating, Ceres gets in the road, and splat, snowball in the ear for Ceres.

Now what else can I think of, there should be a measure of volatiles, a lot of methane still being given off, might suggest an icy moon impact debris fragment from the outer solar system that is recent.
Only water ice being found might suggest either, a Jovian icy moon source, but, do the Jovian moons have clathrate? That might hang around for quite a while at Ceres distance from the Sun.

Can anyone point any theories out to me for Grooved terrain formations like what seems to becoming visible and is also seen on Phobos?

Be almost funny if it was a chunk of Pluto that has recently hit Ceres.

Thanks for the info Dfortes : I was not aware about this.
How sad ! No much announcements were made, despite the world of planetologists lost one of its biggest figures.
A tribute to Gerhard Neukum and to his founding work

I don't think the approach geometry to Ceres is the same as the one we had to Vesta. Knowing what we know of Vesta, could a different approach geometry have shown any bright spot as the one we see now on Ceres?

To show the dark ring is a real feature and not a shadowing effect, I've drawn an ellipse on an OpNav-3 image, representing the crater perimeter. Notice that the dark material in the north east quadrant extends outside the crater wall, where the slope actually faces the Sun. This darkened surface also appears in the RC2 image PIA19185, despite the lower Sun angle, and must be associated with the spots in some way. I previously suggested soil disturbance as the cause, because Ceres has a similar albedo to the lunar surface and the astronauts left dark trails wherever they went. To have a recent impact coincide with the centre of a crater though, seems a bit far fetched to me.

Click to view attachment

I was really excited by the "dark ring" early on, but am now leaning towards the idea that it was an artifact created by image processing on the images released by the project; e.g., a high-pass filter might give negative "ringing" around a bright point-like source.

I can't get the geometry right in my mind for the dark ring to be shadowing from a plume, because such a shadow should have appeared "below" the bright spot in the image you posted, on the side facing the terminator. And the crater in which the bright spots are located doesn't look deep enough for the dark ring to be the shadow of the crater rim cast against the floor, either.

So, from what we've seen, I'm guessing the dark ring is some sort of an non-real artifact induced by image processing or such. However, the bright spot and whatever's going on there are so intriguing that I'd be very happy to be proven wrong!

(And MPI does say the main bright spot is unresolved in the latest images, I've seen that quoted in a few news articles. So we could be seeing a saturated PSF. Ah, to have the raws to play with!)

The best argument for the dark smudge being real - it shows up (along with others) in the Hubble images. See post #1 in this topic. I would argue it is present in the newest images... but the phase angle makes it harder to see. Similarly, some of the more diffuse bright spots are difficult to see in the latest images despite being clear in Hubble and early opnav images.

Phil

I see that Dawn is communicating with Earth now, is that standard? Next imaging session is on Sunday, and the 25 February images should be on the ground already.

If nothing comes out today today, then the press conference on Monday is probably a good bet.

I certainly was't expecting the OpNav 4 images to come out today, but it would be cool if they were ready for release on Monday. They have 33 extra pixels across and 0.4 px/km better resolution than RC2, so they have some potential; even if crescent.

(apparently, they add almost exactly one extra Hubble resolution over RC2, which makes them sound even better )

I always enjoy reading everyone's suggestions. To be honest I don't think this is one of the most likely scenarios at the moment, but my opinion is irrelevant. We shall see what we shall see in the fullness of time. Not every race is won by the favourite.

I think escaping steam from the soup wells, freezing as ice on the surface, is more likely. Of course these extremely shiny, bright spots could be dustbin lids too.

In all three images, the right hand limb shows massive cratering with many appearing pretty deep. I wonder how much the phase angle is flattening out the terrain in the centre and left of the images. Ideas of surface relaxation might be premature unless the surface material varies around the globe. Having said that, there do seem to be clear signs, just on crater density alone, of resurfacing smoothing the terrain on more than one occasion.

Given the high level of surface disturbance and hence mixing of ice with dirt, it might be that "clean" undisturbed ice below the surface regolith, only occurs in a few spots accounting for the anomalous white spots. We have seen how much the phase angle affects the brightness of the mixed ice/dust material on 67P and grain size of the regolith might have a part to play as well. Prognostications on the nature of the "White Spots", fascinating though they are, therefore, seem ill advised at this point. The plot thickens!

The intriguing dark "saucepan handle" basin near the South Pole appears not to be in these images, Dawn has moved too far North. Judging from how far the " Great White Spot" has moved "South" in the third, single image, this would seem to be the reason.

Yes, and that may be mainly at the bottom of large old craters.

I seriously doubt that the CWS or the other bright spots we see are from iron asteroids crashing into Ceres. For one thing, especially in the case of the CWS, the primary white spot seems coincident with the central peak structure of a large crater. The impactor that made that crater would have been completely vaporized, and the vapor ejected far and wide, not concentrated in the center of the crater; the size of the crater makes it impossible for it to have been made by a low-velocity impact.

I admit that there could have been a smaller, lower-velocity impact that coincidentally struck the central peak of an older crater. But something tells me that we're looking at some kind of phenomenon related to the morphology of the central peak of the crater within which the CWS dwells. In addition, I will point out that Ceres has been observed to have periodic emissions of water vapor, suggesting geysers or other types of plumes. This is the kind of thing I'd expect to see from small, locally active cryovolcanos, with limited fields of fresh snowfall (so to speak) deposited around the plume sources.

We're obviously still way too far out to see any evidence one way or another, and the most likely scenario is probably that we're seeing fresh impacts which have exhumed fresh, bright ice surfaces that haven't had a chance to weather yet. But I like the idea of the fresh fields of snow surrounding cryovolcano vents, and I wouldn't count them out yet.

-the other Doug

I was wondering - if the bright spots are of volcanic origin - whether the crater that they sit in could actually have been excavated by a weak wind accompanying the outgassing activity; a bit like the 'wind' on 67/P manages to create ripples on the comet's surface. The crater has not been expanded by the dimmer bright spot as it is a much weaker and/or newer source than the brighter spot (theoretically, a landslide from the crater wall could be sitting right next to it).

That said, it makes a lot of sense that both of these bright spots are fresh impact craters by very small impactors that exposed material rich in water ice or some other relatively bright material. The fact that one of those bright spots sits right in the middle of a bigger crater would then be pure coincidence. It looks a bit like there are two landslides in the crater: one to the south and one to the east. They could have been triggered by two small impacts.

How's this for an explanation? An unusual characteristic of the crater (for its size) is its apparent bowl shape, the bottom of which contains cracks that could become conduits for any pressurised water below the ice shell. The source of that hydraulic pressure may be the gradual freezing (and expansion) of ice at the ocean interface. The easiest route to the surface could well be in the centre of the deepest craters. Water escapes, freezes, sublimates, and leaves a patch of salt residue on the surface. Ceres may only need to have one geyser in operation at any particular time to relieve that pressure. Patches of salt from defunct geysers gradually fade and disappear over time, under thin layers of ejecta dust from minor impacts elsewhere on Ceres.

It's more pristine than some other craters of its size on Ceres; that much I agree with. The rest, for me, is too much inference on too little evidence. Let's wait . .

Thing is, we don't have any rocky bodies of similar size to compare to. Maybe this is just what bodies of this general size (or mass) end up looking like, regardless of composition?
(Rocky bodies are really rare in this solar system...)

Has anyone done a comparison chart of small solar system bodies with accurate relative albedos? The captions to elakdawalla's excellent charts don't say that they've been assembled with care over relative albedo.

When thinking about the possibility of the bright spots being 'volcanic' in nature, I keep recalling the 'Ina Caldera' on the moon:

https://www.google.com/search?q=ina+caldera...-8&oe=utf-8

This isolated structure appears to be an instance where relatively very recent outgassing has 'scoured' away the overlying regolith. What is the source of the gas? Who knows, but the process could possibly be similar to that (any) on Ceres.

Ina is not unique any more, dozens of features like that have been found in LRO images.

Phil

http://www.sci-news.com/space/science-geol...moon-02205.html

Ok. 'Unique' edited out.

While working on the alignment issue Phil mentioned, here an intermediate comparision of two overlapping RC1/RC2 images, most of the images registered to less than one degree error relative to each other:
Click to view attachment Click to view attachment

The other RC1/RC2 pair now matches pretty well, too:
Click to view attachment Click to view attachment
With the same parameters the RC2 image of the "bright spot":
Click to view attachment
Horizontal shifts (longitude) may still be incorrect. The position of the poles on or near the terminator may also need to be corrected, I hope not too much, since the ellipsoid shapes match sufficiently well. Checking and adjusting this will take me a while, so I'm providing this complete preliminary RC1/RC2 set.

Adjusted OpNav3 merged map:


Some longitude adjustments RC1:


and RC2:


That's now the best fits I could achieve.