Excellent find, Phil! That's exactly the kind of image I was looking for.

And, see -- once you locate hardware on the surface, the low sun images are actually helpful in characterizing them. The high-sun images would never have implied the amount of the retro-rocket that survived its final plunge intact.

-the other Doug

Yes -- Both Spudis and Wilhelms (two of my favorite lunar science authors) give kudos to Baldwin. And wasn't it Baldwin who, after holding stubbornly to other theories for a time, finally pronounced Barringer Crater an impact feature?

I completely agree, Baldwin is seminal for impact theory. And much of the later work, from many people including the above-mentioned, has expanded on the dynamics of ejecta formation and re-emplacement, shock effects on the impact targets, and development and emplacement of impact melt sheets on rocky bodies and also on hydrated rocky bodies like Earth and Mars. And on the propagation of energy into the impact target, something I think is key to the festures we're seeing on Ceres. I think a lot of the cryovolcanism we're seeing might be the result of impact-generated temporary heating and agitation of Ceres' icy mantle (or perhaps subsurface ocean/convecting warm ice mantle), causing sudden movement and eruption of subsurface materials.

It appears that there has also been ejecta splash resurfacing going on around the larger basin-forming impacts. And the large, extremely relaxed basins we see wouldn't just have relaxed like that immediately -- the impacts would have moved and displaced a lot of the material around and below the impact site, which would have pushed back in (and up) to raise the basin floors back up. That movement would affect the entire mantle in one way or another, and I bet it would cause cryovolcanic processes and features.

Of course, all of this assumes that Ceres has some kind of either liquid or convecting warm ice mantle, and makes some assumptions about how globally contiguous of a unit it is. I'd be interested to see if some of the first papers to come out on Ceres from the Dawn data will deal with the qualities of the mantle deduced from the imagery and the spectroscopy...

-the other Doug

Bill, you posted that exactly as I was bringing the thread up to post the same thing. These craters may be impact-formed, but if so, the target material has far different properties from what we've seen on rocky worlds, and also far different from what we've seen on icy worlds farther out from the Sun. Some of these flows look more like they were blurped onto the surface, not thrown as ejecta or erupted as volcanic units. More like a they were vomited onto the surface.

I wonder how much difference it makes that Ceres is too close to the Sun for the exposed ices to completely resist sublimation, yet too far from the Sun for a world with so much water to be primarily rocky. We're in a different thermal environment for a watery world than we've seen before. Perhaps that's what is driving the strangeness we're seeing in the surface features.

-the other Doug

Interesting rock. It's obviously layered, thus implying a sedimentary rock of some kind. And yet the lower, less wind-smoothed portion looks like it has small vesicles in it. Since finely layered rock is less likely to be vesicular, I'd have to think that these are places where small grains have eroded out, or dropped out, of the rock. Either that, or the little holes are tiny craters left by energetic ejecta from nearby impacts.

Of course, I suppose it could be an example of a sedimentary rock that was partially melted via impact, thus forming vesicles. The distortion of the layering on the upper portion of the rock could also speak to partial remelting, too, I suppose.

-the other Doug

Very, very good points, JRehling. You're absolutely right. And I think JohnVV has a good point, too -- and one that the team who announced this discovery mentioned -- that 452b may very well be a giant Venus at this point, what with the extra insolation it's getting now due to its star's advancing age.

The rate at which water would be driven off by the solar wind, as seems to have happened on Venus, would also depend on whether or not 452b has a magnetic field, would it not?

-the other Doug

In re the question as to whether a 1.6x Earth mass planet could be a rocky planet, vs. if such a planet would become Neptune-like -- wouldn't that depend a lot on the nature of the planetary disk from which the planets formed, where in the system it formed (i.e., inside or outside of the frost line), the dynamics of the other planets in the system, etc.?

I've heard speculation that the migration of Jupiter in and out "stole" some of the material that would otherwise have been available for Mars' accretion, gathering some of that material into itself and scattering the rest into our asteroid belt. So, depending on the dynamics of other planets in the 452b system, as well as the original composition of the planetary disk and the timing of the star's T-Tauri phase (which would have blown gasses out of the inner system) and, of course, the impact of being inside the frost line when you develop enough mass to begin to accrete a large gaseous shell, perhaps it is quite easy to develop a fully rocky planet of the size of 452b without passing over into becoming a Neptune-like object?

I think it's a little simplistic to state that all objects above a certain size will become Neptune-like, when Neptune itself is defined by a lot of factors that would not apply if such a body formed far closer to its star than Neptune itself did...

-the other Doug

I actually wasn't aware that there were no plans whatsoever to do any imaging during the transition to HAMO. Thanks for the reassurance, guys.



-the other Doug

Still no images posted that were taken after June 25th. Are we expecting newly-acquired images in the next week or two?

-the other Doug

Looks like tectonic cracking of the surface, which is somehow exposing material of different composition than the surficial layer. Maybe there was an ancient impact basin here and the underlying crust still "remembers" the cracking, which serves as a conduit for material slowly being moved to the surface?

-the other Doug

Also, I've not seen this mentioned specifically, perhaps the weight of the equatorial ice cap that is Tombaugh Regio is compressing the underlying water ice crust and causing the tectonic cracking we see around the region. Specifically, I'm thinking this could be the mechanism that created the radial cracks coming away from the region and extending into the Cthulu region.

That would make as much or more sense to me as the radial cracking being caused by an impact. Other basin-like impacts into icy worlds, like Callisto, for example, generate cracking in concentric rings around the impact point. These are cracks extending outward radially from the center of what appears to be a gigantic pile of nitrogen ice covered by a layer of CO ice. The weight of that pile could be what's deforming the surrounding terrain and causing the radial cracking.

-the other Doug

Aw, gee -- and I was just flipping through the on-screen program guide on my cable TV service looking for some actual news (it's getting to be a lost cause watching the American cable news networks if you want to see actual news) and I am afraid to say I passed by the BBC World News channel because it wasn't the news segment, it was the Click show.

I'll have to see if they're re-running it later. I rarely see anything about my real life (things like this forum) spilling out into the world everyone else sees. It's reassuring to see it happen. Thanks, Ian!

-the other Doug

Thanks, Phil! Yeah, that was the thing I saw in the early LROC images of the Surveyor III site that I thought might be the retro. Somehow, I don't recall seeing that thread -- and that's unusual for me. Again, I plead painkillers...

I agree that it's going to be way easier to find hardware on the Moon in the LROC images taken at very high sun angles than the low sun angle images, and I must say you've been having great success at it. It's great to see every new little bit of hardware we've left up there, and you more than most have been the best at finding things. It's a privilege to watch.

But in some cases, after finding the stuff, it also seems to me that it can inform the "dark blob" images if you know if there are, say, local slopes or other landforms that act to modify the piece of hardware's "look," and that aren't very obvious under a high sun. The kind of stuff you would see much better at lower sun angles. So, just sort of thinking, if after finding things, do you also look at them at lower sun angles, too? Are they usually available at the same resolution at lower sun angles?

Or is it something of a crapshoot, even now?

-the other Doug

So... the new detail of the majority of the northern hemisphere, particularly the polar plains, is really very interesting when it comes to cratering.

The entire region looks like it retains shadows of an ancient, heavily cratered terrain, but that the ancient terrain is heavily eroded. (I was about to say "weathered," and that may yet be the correct phrase.) It looks like craters larger than 50km or so are all ancient. And I see very little indication of any fresh craters of any size.

I don't think we're seeing merely effects of frost deposition/sublimation. A lot of new material has been added to this terrain, and the remains of the crater forms are both filled in and eroded away. So, while the resurfacing here isn't completely covering up and destroying the old terrain, I would argue we are seeing slow resurfacing happening, that over billions of years is very slowly erasing the early cratering history. Give it another couple of billion years and the crater remnants may go completely away.

There have also been tectonic deformations that have wiped out ancient cratered terrain around them, as well as transforming ancient craters into long troughs and connecting several into local elongated depressions. This, too, acts to reshape and resurface the terrain.

So, even though we do see remnants of the ancient cratered terrain, I don't think that means there is not a resurfacing process that continues to this day.

-the other Doug

Looks like Surveyor V's retro-rocket (if you have it correctly identified, and I think you do, Phil) might have rolled a distance before it came to rest. They weren't coming in fast enough to dig deep craters, so I guess it doesn't surprise me that one might roll a bit.

Since at these high-sun conditions the topography becomes completely washed out, it's hard to tell if maybe V's retro might not have rolled down into a shallow crater. As it's darned near impossible to get the original TIFFs from the LROC website anymore, I don't have the best way to go looking for lower-sun images of the site to check for such a shallow crater. Could you take a look and see if my theory holds any water, here, Phil?

Oh -- I looked upthread, all the way to where I began the thread more than five years ago, and I didn't see any posts of the likely Surveyor III retro's final resting place, even though I know I've looked myself and have suspected a suspicious object to the north of the landing site. Could you point me to where you posted your identification? I'd like to look at it myself (assuming I haven't already -- age plus the heavy painkillers for so many months before and after these darned surgeries have not done good things for my memory, it seems).

-the other Doug

But, Sherbert, that far out in the solar system, comets have no tails. Cometary tails are created by sublimation of ices and scattering of entrained dust by a much closer Sol. I don't know of any comets developing tails outside the orbit of Uranus, much less Neptune.

-the other Doug

Well -- the other big thing about this new discovery is that it's a planet orbiting in the habitable zone of a sunlike star, and thus, unlike those orbiting smaller stars, is far enough away from its star to avoid tidal lock. I has a 385-day year.

Even if it's five Earth masses, it's roughly 6 billion years old, and has spent almost all of that time in the habitable zone of its star. And hasn't been tidally locked to its primary. I have to think that life is more possible in such a situation than on a smaller planet orbiting a cooler star in less than 100 days that always shows the same face to its star.

-the other Doug

All right, so, if they are seeing hazes over Occator at mid-day, where are the images that show this phenomenon? Will they be embargoed until someone can have a paper published about it?

-the other Doug

I know. I just hadn't yet seen an image acquired since the safing event, and was a touch concerned, is all. I have no problems with the beautiful images the team does post, I appreciate the Pictures of the Day a lot. Loved it back at Vesta and love it now.

I just asked because it had been a couple of weeks since the safing event and hadn't seen anything indicating they were taking pictures again. Thanks for the reassurance, you guys.

-the other Doug

And, as usual, when playing with numbers, I got one wrong. Somehow I thought I had just read Pluto loses 5 tons of nitrogen an hour. I find I left off a couple of zeroes, it's 500 tons an hour.

So, I believe that makes the amount of nitrogen lost closer to 16.33 quadrillion tons over four billion years, and that's more like (if I'm figuring the scientific notation right, that was always hard for me to think in) 1.25e-3 percent of Pluto's present mass. More, but still a pretty small percentage. Nothing like the half of a percent that was estimated as little as ten years ago by those who anticipated a lot of gas loss from our favorite little KBO.

-the other Doug

Hmmm... the darker, wormy-grooved terrain is also present in the southernmost of the two new images, and while the grooves in what I'm calling the wormy terrain aren't exactly straight (they have more of a long-wave pattern), they are all more than roughly parallel to one another. (The small grooves, not the wormy terrain itself.)

Their direction is also generally north-south, with a little northwest-to-southeast component.

My guess in my WAG post about seeing a lot of signs of what looks like wind erosion (or at least gas transport erosion, which is basically the same thing) may turn out to be a good one.

-the other Doug

Kewl! Good to have a thread where we can speculate wildly. (ADMIN: With some restraint please. )

I'm wondering why the CO ice is all in Tombaugh Regio on the lit side of the planet. What would cause CO ice to gather just there? Altitude? Temperature? Is there a liquid CO "aquifer" underneath that only wells up here?

Remember that the area is getting the most insolation it will get during the northern summer. Yes, it gets more direct sunlight when the sun is high over the equator, but only for half a Plutonian day, so overall right now, even at a lower angle of incidence, it's getting insolation continuously. So it's not exactly a cold sink.

I think you have to start getting your head wrapped around the 248-year cycle of seasons on Pluto. It spends more than 50 years in each season, and more than a century of continuous insolation on each pole. Cold sinks are going to appear in odd places, build up ices, and sublimate back off as this cycle continues. And I'm thinking that each set of seasons are unique -- topography changes, ice deposition occurs in different places due to vagaries of wind and even weather -- so major ice depositions might occur in different places in different years.

Maybe the CO ice is a remnant of a major deposition that occurred in the best cold sink available on what was then the dark side when a big exposure of CO ice sublimated relatively quickly from the southern hemisphere? And the other ices deposited at the time have preferentially sublimated since the northern hemisphere began its summer, leaving only the harder-to-sublimate CO ice? If so, what around here sublimates more easily than CO ice? And maybe the pitted surface at the southern edge of Sputnik Planum is an example of where those other ices puffed out, leaving holes in the CO ice?

Also -- hitting the various things that have been crossing my mind -- if Pluto is losing 5 tons of nitrogen an hour to space, over four billion years that amounts to nearly 163 and half trillion tons of nitrogen, if that's been a relatively consistent loss rate. How many tons of Pluto is left? How much of the original body has been blown away? And how much more of other lighter elements might have been lost earlier in Pluto's history?

And, to answer my own question, a quick search shows me that Pluto has an estimated mass of 13 quintillion tons. A quick calculation tells me that the amount of nitrogen lost (again assuming a consistent loss rate) is 1.25e-5 percent of Pluto's current mass. So, I guess maybe not so much... sounds like a heck of a lot, though!

-the other Doug

Yep, those are swear-jar images, all right!

Looking forward to the high-res images, now. Going to be really, really interesting.

-the other Doug

I was working during the presser and y'all are making all these wonderful comments, but no links to any images. Are they not available yet except as illustrations during the presser? In other words, how can I see what y'all are drooling over?

-the other Doug

Yes! This is an amazing find. Granites are thought to have formed on Earth when hydrated crust (read: seafloor) is subducted during plate tectonics. Now, trondhjemite (and the TTG suite in general) doesn't necessarily show the chemical signatures of having directly re-mixed with mantle material, so finding the stuff on Mars doesn't absolutely prove that Mars had what we would recognize as plate tectonics. It's a pretty sure sign that some crustal subduction of highly hydrated rocks did occur, though, of some type.

Unless, of course, this is an example of a piece of Earth's Archaen crust that was whacked into space by a big impact and transported to Mars, just as Martian meteorites have been found on Earth. That would seem to be less probable than Mars creating its own granites, though, I think.

-the other Doug

Pluto spends most of its time in a region of the solar system that would be quite similar, in terms of the number of potential impactors, to where Neptune and its moons are located. I would say that crater counts on the Neptunian moons (with the possible exception of Triton, since it was captured at some point and potentially altered during the capture process) should correlate with crater counts on Pluto/Charon.

In other words, if we see significantly fewer craters on Pluto/Charon than we do on Neptune's "natural" moons, then they are being resurfaced and are likely more active. If not, then the Pluto system is about the same age and/or has the same activity history as the Neptunian moons.

From what I was hearing today, the impression I get is that the science team feels strongly we're talking about the former, and not the latter, in their initial observations.

Since both Alan Stern and John Spencer post here frequently, I'd love to hear their takes on why they made the statements they made today. And, hey -- they have lots of time to post now, right? It's not like they're really, I dunno, busy or tired or anything right now...

-the other Doug