The crust of Ceres seems to have a lot of fissures into which material slumps, leaving an excess of crater-like pits. That's what I think caused that horizontal band of small craters on the floor of the big crater in the latest image, and grooves on part of the rim.

The cause became clear last week when I noticed a multitude of pits in the plain south of spot 5 (lower left corner of PIA19560) are aligned in closely-spaced rows, revealing the location of dozens of fractures criss-crossing the region.

One of the albedo spots visible in OpNav3 images that I've been interested in seeing up close, is the central mountain complex of this deep southern basin.

Lo and behold this feature appears to be located at the intersection of several long fracture lines. Of course, central hills are a frequent consequence of impact, but on Ceres they tend to be the same low albedo as crater floors and everything else, unless (in my opinion) such sites have been active after formation of the crater and fault lines.

There are at least three possible volcanic cones associated with this spot. I've inverted the image so it is illuminated from above.

The spot lies on a fault line running from the top left to the bottom right corner, but is indistinct at this high sun angle. As far as I can tell, hills are at the centre of all spots, whether they lie within craters or not.

Here's the general course of that fault.

Like the large mountain spot and another spot of small cones near that, the bright spots coincide exactly with fractures in the crust. The great length of some of these faults is a definite sign they run deep.

"There appears to be a dark linear feature extending between the bright areas"

It's part of the regional system of parallel grooves. This particular one extends well outside the crater rim on both sides and joins up with the most prominent groove about two crater diameters to the ESE. Some minor spots in the crater are not aligned, so I expect we'll see more cracks show up there as the resolution improves.

The largely resurfaced region south of the crater with the bright spots is devoid of medium to large craters, but curiously is peppered with more small craters than older terrain.

Suppose mud flows carrying giant icebergs covered this area; shouldn't frozen mud quickly develop its own insulating layer of dust, but pits will be created as the relatively pure icebergs sublimate away? Maybe the outer 10km or so of the crust is made of frozen mud, with pure ice further down. That would explain why there's no evidence of ice having been exposed in larger craters and causing erosion there.

There's enough evidence in the RC3 images to make some preliminary conclusions on the unusual features we see.

MOD NOTE: No, there isn't nearly enough evidence yet to draw conclusions. Currently there is an extremely limited amount of data which may be used to formulate very tentative hypotheses which will be accepted, revised or discarded based on additional evidence and critical review. Key difference.

EDIT: To avoid misinterpretation, the gist of what I failed to convey properly in my first line follows.

I see enough evidence in the RC3 images to comment on what I believe the unusual albedo features are and speculate on how they formed.

1. The extensive grooves represent deep cracks in the crust, rather than crater chains from secondary impacts.

2. The spots are volcanic cones associated with rift valleys and fault lines, rather than craters exposing more reflective material beneath. That should become obvious to all when Survey Orbit images are released in June. The vents gradually expel cold ocean water, as a safety valve to equalise the pressure caused by expansive freezing on the underside of the ice crust. The water oozes out and freezes or falls as snow, before sublimating and leaving permanent deposits of salt behind on the surface. The mountain visible since February appears to be the largest such structure on Ceres, but is dormant or extinct judging by the dust gathering on its summit. However, the brightest spot/s could well be active and have ice close to their vents - something on Ceres is producing enough water vapour to be detectable from Earth.

3. The dark patches of chaotic terrain are also associated with fault lines. They probably represent sudden flows of rock-bearing mud, flooding out when major impacts occur elsewhere on Ceres and oscillations in ocean water pressure force some plates to gnash and grind against each other. The grooves become indistinct there because of that flooding. The southwest rim of Piazzi crater and the northeast rim of 'bright spot' crater are obvious examples of this, but there are others in the southern hemisphere we haven't seen in detail yet. I won't be surprised if all such regions have grooved terrain and volcanic cones associated with them, because they represent areas where water can most easily reach the surface.

Has anyone noticed in the RC3 movie, small hills (cones) at the bright spot near the large mountain, and that they and the mountain are both on a fault line, and that this system of faults extends through the crater with the brightest spots of all?

John

Coincidence or not, that paper appears to have been released on March 1, more than two weeks ahead of next week's Lunar and Planetary Science Conference, and a day after I proposed the same volcanism-driving mechanism in post #542, on the 'Dawn approaches Ceres' topic.

They make no mention of salt deposits though, as a consequence of the release of seawater, hence I expect we'll see evidence of that in spectral results from Dawn. Final confirmation of volcanism should occur by May or June, when central pits show up in those bright spots.

I'm no geochemist but I'd assume carbon dioxide was driven off when Ceres differentiated and formed the ~100km-deep ocean that theoretical studies predict is there. Anyway, doesn't CO2 sublimate at a lower temperature than water ice, and leave no trace when it's gone.

The ocean surface would have froze over and then accumulated a rocky crust. The ice shell could be over 20km in depth by now, judging by the amount of topography it supports. By the way, I calculated the amount of salt deposited over the age of the Solar System if the driving force was the gradual freezing (and expansion) of the underside of the ice shell. Interestingly, there's enough to build many 5km-tall volcanic cones, without requiring any heat sources.

The cylindrical map is inexplicably low in resolution and doesn't show fault lines well, so I've drawn some on. Notice that one bright spot is adjacent to a fault line and the other (a large isolated mountain) coincides with a junction of two fault lines.

Nice bullseye pattern! If that's an old impact basin, it's diameter is either 380km or 630km, depending on which of two ridges is part of the rim.

The circumstantial evidence for ice volcanoes is growing. There's a diagonal fault line below centre, adjacent to which is an isolated mountain about 20km in diameter and 5km high, that just happens to be one of the bright spots. Then there's the bright spot on the prime meridian that has rays like an impact crater but the broad base of a caldera. It's near the terminator in the last image of the rotation sequence. No wonder the Dawn team is puzzled!

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.

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.

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.

The major bright spot is 15km wide and lies at the bottom of a rather deep 95km crater and is brighest (freshest) at its centre. The crater is deep relative to others because it formed after the ice shell grew thick enough to support the floor without flooding. Nevertheless, its age is likely to be in the billions, rather than millions of years. If the spot was a benign patch of material, ejecta from elsewhere would have covered it on geological time scales, so we can be confident there has been some sort of activity there. The fact that the dark ring visible in lower-resolution images is offset from the crater, is further evidence of activity. Perhaps this is an active or sporadic geyser shooting out to the right - the water turns instantly to ice and lands at that elongated spot within the crater. The dark ring might be a consequence of soil having been displaced.

The extensive network of crosshatched grooves is likely due to expansion of the ice shell as it froze, but larger rift valleys seen in earlier images seem to be associated with major impact basins.

Most here will be well aware of Marc's last blog post. Note that OpNav 3 took place a day later than listed there. I'm not after approximate figures - there'd be no point. If I could get distances at two times around Feb 4.4, I could extrapolate them for individual images within 100km and make some measurements; to clear up a discrepancy between the diameter measured by HST and a well-observed occultation -- or we could wait who knows how long for official figures. I already have a figure for the sidereal rotation period over an eleven-year interval!

The direct link for Dawn's view of Ceres is http://neo.jpl.nasa.gov/orbits/fullview2.jpg

I've captured 50+ images of that page since February 7, in order to extrapolate distances during imaging sessions. Has anyone recorded distances covering OpNav-3 around Feb 4.4?
The figures on JPL/Horizons are completely in error and evidently based on outdated orbital elements.

According to separate comments by Marc Rayman over the past few weeks, the albedo of the Region A spot in OpNav 2 images was about 50% higher than for the average surface (0.135), increasing to 0.25 by the time of the higher-resolution images of RC1. I don't see how it would only increase by a factor of 1.85, when the image scale increased by 2.85 and the spot was still unresolved (limited by the pixel scale). In theory, shouldn't the albedo increase to 0.385 in that case, or is the math not as simple as that?

Ceres is turning out to be quite a world of its own. Obviously we have two large impact basins in the southern hemisphere, flanked on both sides by a network of crater-erasing rift valleys, stretching halfway around the globe. One or both impacts may have penetrated and split the (then relatively thin) frozen part of the mantle in the process.

The Piazzi region is bizarre! It's difficult to be certain from a single image and lighting angle, but when I look at those sinuous features, I see snakes and tadpoles with their tails pointing downhill into the large basin from both sides, so they could be vents of some kind. There are also many isolated molehills coming into view as we get closer, that cannot be a product of impacts alone.

The enigmatic bright spot at Region A is equally interesting. Conceivably it might result from an impact by a class E or V (high albedo) asteroid, but serious doubts are raised by the total absence of rays. If it's not an impact, it could be a deposit of salt from a geyser, after the ice has sublimated. The fact the spot is encircled by a dark ring reminiscent of those on Io, may not be a coincidence.