Which makes this particular example sound more like a hot Jupiter that is in the final stages of losing its atmospheric mass, rather than a super-Earth that developed with a largely hydrogen/helium atmosphere in the first place.

So, I hate to say, I don't think this says anything about the atmospheric constituents on super-Earths that are not also hot Jupiters that have spiraled in to their suns so far that they are orbiting every 18 hours...

-the other Doug

A perfectly aligned stream of cometary bodies (or at least bodies of similar size), that was gravitationally liberated from some star system by a passing star or other massive body, could appear dark from Earth if there is no nearby star to light it up, and could be narrow enough that it would not occult other stars in the nearby starfield. It's the latter constraint, the lack of any abnormal dimming in the nearby starfield, that constrains the option of interstellar occulters more than anything else, but a one-in-a-billion configuration might result in such a stream of small bodies that would only occult the one star. Variations in its density along the stream could result in the odd ups and downs we are seeing -- the stream might be passing between us for some time, but only the densest stretches of it are detectable.

It's just not a very likely explanation, I fear.

Just a thought -- is the leeward side of an active dune the best place to sit, from a dust-pileup perspective? I can image small-grain material (dust and small fines) blowing over the top of an active dune and landing on our intrepid rover...

-the other Doug

We had this problem when MSL first landed, that the navcams in particular looked really, really dark. And the mastcam images looked rather dark, too. Sometime in the first two months after landing, though, they brightened up considerably; the scaling was obviously adjusted. The example ugordan posted looks a lot like those early navcams. I wonder if something got reset back to the original scaling rather than the scaling they've been using for the past three years...?

I do recall posting, in the first month after landing, that the darkness of the images rather defeated their purpose for public outreach. I said that people would say "Why is this place such a darker, gloomier place than the other places on Mars we've landed?" when the only thing that's happening is that the scaling on the MSL images is very different from that used on the images returned by earlier landers. But the problem did go away -- at least until now.

-the other Doug

Oh, yeah -- it looks like you've definitely nailed it. If that's not the Surveyor VI retro-rocket, it's a very, very coincidental impact of exactly the right size, and in exactly the right place, that came from something else.

I still think the items with the highest cool factor would be to find the impact sites of Surveyors II and IV. I know that at least one of them is likely to be a small field of little craters, since it's likely that its solid-fuel retro exploded. But it would be really interesting to see the resulting impacts. (Doubtful they would be discernible, more's the pity...)

-the other Doug

I'll wait until the LAMO images of Dantu to say that the jury has reached a verdict. But the one thing that makes me think that Bill might just have something, here, is that the "after" image shows the development of small apparent sinkhole-type craters within the now-you-don't-see-it, now-you-do graben structure. That are not visible at all in the "before" image.

I agree that the graben itself can appear to vanish depending on the sun angle. But all of the little craters of the same size in both the before and after images are clear and distinct. Why would they not appear based on sun angle just because they are along the bottom of a graben? Sun angle wouldn't stop the far walls ("far" meaning facing the sun) of those craters from being brighter, and the near walls from being in shadow, right?

I'm sure that the LAMO images will give us a better understanding. Sure wish we had LAMO images from the before and after timeframes, though...

I think you may be right about Dantu being a feature above a subsurface plume of some kind, Bill. There has definitely been deformation within the crater floor.

For example, you have the arcuate crack-like graben along the right side of the central "peak" area (in the published image -- I've little idea what to call north, east, etc., here). Per John's excellent renderings, it looks like this side of the crater floor is predominantly lower than the left side, making the arcuate graben look like subsidence cracks.

But directly to the left of the central complex, you have what looks like a deflated dome structure. It looks very much like a dome developed just to the left of the central complex, and then the plume pushing up from below collapsed, leaving the sides of the dome pushed above the neighboring crater floor but the center of the dome collapsed to something between a flattish mesa and a shallow bowl.

And, as with several of the larger craters on Ceres, the central complex looks more like a collapsed caldera than a rebound peak. At the very least, if there ever was a rebound peak, there are only remnant ramparts left of it; the center is all gone. And in a roughly circular form -- making it look a lot more like a collapsed caldera than an oddly inside-out eroded rebound peak.

If the central complex was a caldera and the plume shifted to the left after it was originally opened up by the Dantu impact, then you could conceivably have had a cryovolcanic caldera appear and then collapse right where rebound was greatest. Then as the plume moved (or the crust moved over it), the ground underneath the area to the left of the central complex was deformed up. This would have served to deform the right side of the crater floor in such a way that the arcuate graben were formed.

You have to wonder how much time passed between the initial central complex activity and the doming deformation of the left side of the crater floor. Since the graben on the right side of the crater floor seemed to form along both the lowest point of the floor and along the tops of adjacent draping units that were obviously tossed into the crater after its formation, you get the feeling that the graben didn't form until after Dantu had relaxed a bit, and after it had suffered some infill from nearby impacts which tossed in the younger draping units.

"Younger" being relative, of course. It could have been a process that took place over millions of years, and ended billions of years ago...

In the sub-frame, the white "clasts" look almost sparkly -- like a granite.

Are we seeing any granitic signatures from this bed, I wonder?

-the other Doug

It took me three tries to load the website yesterday, but when it finally loaded I found that I could pull up whole-Earth images from two days prior -- which happened to be my 60th birthday. It lets you scroll through images taken a few hours apart throughout a given day.

I was able to capture the image of the western hemisphere, featuring my home continent, as it appeared in the middle of my birthday. Kewl! I now have it as my desktop.

-the other Doug

My understanding, from reading a variety of speculations about Pluto's internal structure, is that water ice is lighter than some nitrogen ices, heavier than others, and heavier than liquid nitrogen. So perhaps water ice is subducting into zones where it is indeed heavier than the mantling material. And, of course, the mantling material may not be pure nitrogen ices or pure liquid nitrogen, there may be other solid/liquid/slushy gasses mixed in which could affect the density of a given mantling zone. Remember that some light granitic "float" material on Earth ends up being subducted in some places, along with the heavier, highly hydrated seafloor material. It's not a black-and-white kind of thing.

Also, crustal spread requires either crustal pile-up at plate boundaries or sliding some crustal plates underneath other crustal plates. Some subduction, in terms of plates sliding on top of one another, will occur from mechanical forces alone.

-the other Doug

I will bring this over here, since it's rather speculative. I've made a mention of the concept in the primary thread, but this gets even more speculative.

I'm thinking that we're seeing actual plate tectonics on Pluto. The plates appear to be smaller and more irregular than we see here on Earth, but it seems that the whole Tombaugh Regio may be the equivalent of seafloor spread, pushing plates of water ice away from it. This would mean that all of those fold-edge chasms we see are actually subduction trenches, where the water ice crust is being forced back underneath the surface, into a "molten" (or at least plastic) mantle composed of similar materials to what we see spreading out onto the surface at, say, Sputnik Planum. The plate movement, and plate collisions, could also account for the raising of the water ice mountains.

The snakeskin terrain could reflect surficial folding from the pressure of plates being shoved along and into each other.

What do you think?

-the other Doug

It seems to me that the confirmation of liquid water mostly impacts landing site selection for future missions, in that the planetary protection protocols specifically prohibit any landings near liquid water with any lander at a sterilization level less stringent than that defined for the Viking landers (i.e., less than 30 spores per vehicle). Otherwise very attractive sites may end up on the verboten list if there are close-by RSL's.

Any idea if this might affect the landing site selection for the 2020 rover? Especially considering the fact that the 2020 rover will be caching samples for potential return -- if you land near RSL's, you have to postulate not only sterilizing the rover to the Viking standards, but also whatever follow-on vehicle collects the samples and returns them to Martian orbit...

-the other Doug

Agreed -- they show exactly how thick some of these draping units actually are, especially where they pile up against the underlying terrain. In the right-most image, in particular, that ridge looks like it could rise up 500 meters or more above the surface it overlays.

-the other Doug

The "snakeskin" terrain looks like it may be at least partially due to tectonic movement of the crust. There are places where the "wormy" texture's lineations are pretty parallel, and others where they seem to fold along a different vector, as a piece of terrain appears to have collided with another.

It looks like small plates all floating on a liquid/plastic mantle are encountering relatively small-scale folding as the plates are shoved along. This is consistent with the apparent movement of terrain away from the "plume" area of Sputnik Planum. Think of Sputnik and the Tombaugh region in general as places where the crust is spreading out, and the deep chasms as subduction zones.

Just a thought...

-the other Doug

A million suns shine down,
But the one here's pretty dim....



-the other Doug

I read a second-hand report that went something like 'we have detected methane but our results have not been confirmed. Analysis of the data continues.' Something like that.

So, it sounds maybe like someone wanted to make a big announcement before peer review has been completed, and was embargoed from doing so until either issues in the data/analysis are resolved, or until peer review is completed.

-the other Doug

Per the JPL website, there will be a presser on Monday morning, at 8:30 am PDT, which features several NASA science directorate types, but includes from current active JPL mission scientists only MRO/HiRISE PI Alfred McEwen. So I'm assuming the "major discovery" announcement was developed from MRO data.

The details are embargoed until 30 minutes prior to the presser, but the headline on the article is Mars Mystery Solved.

I'm looking forward to seeing what they have discovered.

-the other Doug

My swear jar just exploded.

-the other Doug

Just that as early as Viking 1 the surface was recognized, in places, to have a "duricrust" that was much more cemented than the granular fines just beneath.

Thank you! Desktop now in place.

As for the image, all I can say is the following:

"I think it's important to explore beautiful places. It's good for the spirit." -Dave Scott, amateur geologist/explorer

-the other Doug

Thank you, Bill. I've been seeing this for quite some time. I've been calling these draping units "splash-emplaced terrain," and words to that effect, since some of the most obvious examples lie around the larger basins. But there seem to be many overlapping draping units of many ages. It's going to be tough to sort them all out.

-the other Doug

Unfortunately, Flickr now seems to be requiring that you have an account with them, or a Yahoo account, to download images. I know both are supposedly free, but when a website tells me I need to register to do more than browse, I tend to rebel a bit. I don't need or trust people who want to track my movements -- one reason I don't have any of those "discount cards" that are so popular at gas stations and drugstores. What I buy, and where, is none of their business. Same here -- what I download (as long as it's legal) is no one's business but my own.

Too bad, that would have been my new desktop.

-the other Doug

A central, eruptive mound is how the main bright spot appears to me, as well. And while there are a number of bright spots around Ceres, this is the only feature that has the appearance of being eruptive.

-the other Doug

I'm not thinking that the central feature is primarily a raised feature. Be it an impact crater or a caldera, the main bright area is nicely tucked into a circular feature, isn't it? But the very straight cracks, especially the one going straight up in your detail, Phil, are not very deformed by the circular feature. So, the cracks seem to have formed after the circular feature. And while the lighting doesn't give a lot of clues, I get the impression of there being a building central mound within the larger crater- or caldera-like depression.

I also think I may see what Russell, et al, have been discussing -- if you look at the very end of the crack that, again in this detail, runs straight up from the main bright area, there are a couple of very subtle dark streaks in the little bit of brightening around that end of the crack. While I can't, obviously, say this is happening for certain, these streaks resemble shadows cast on the surface from the densest portion of a fountain of material coming out of the top end of that crack. Recall that Enceladus is pumping out a lot of material along its tiger stripe cracks, and yet the only real visible clue it's happening when looking straight down into the cracks from Cassini has been such subtle shadowing.

The area of the secondary bright area, at the 2:00 position from the main bright area in the detail above, is sitting within an irregular boundary of a low, continuous scarp that makes something of a sausage- or cigar-shaped enclosure. Could represent cooling of a once-liquid body, akin to a lava lake, or could even represent a small, irregular caldera-like formation grown from escaping material from a crack that may have once run underneath it. If so, that crack appears to have been completely buried by now.

Finally, look for obvious impact craters. In the entire detail image, I see two very small ones. Even if this is a fairly new crater (and I dispute that, based on the amount of mass wasting I see in the walls), I would expect to see more small craters on its floor. The conclusion is that the floor, in the general vicinity of the bright areas, has been resurfaced by processes far more recent that the creation of Occator.

Now, let's get some LAMO images...

-the other Doug

Now let's see if the NH team can sit on the images and not release them -- because they're so darned cool and they can't resist -- until the Friday release date.

That's one thing I love about the NH team. They are well and truly enthused by their mission and its discoveries, and just can't wait to share their data products with all of us. I'll bet some of the really, really interesting and striking images will be released early. I'm not counting on it, but it would be in character.

-the other Doug