Hmmm... not only are there two specific types of rocks in the B&W images, one appearing white and the other appearing darker gray, there are several rocks in the image which show both rock types within the same rock. You can see in several rocks a contact between the light and darker rock types. And in a couple of cases, the faces are oriented exactly the same on both sides of the contact, so this can't just be an artifact of illumination angle.

I will say that there seems to be absolutely no difference in how the two different types of rocks have weathered -- i.e., those rocks which exhibit contacts don't exhibit weathering differences on the different sides of the contacts. So, whatever is causing the albedo difference is not changing the overall softness of the rocks.

I'd have to think this shows some form of compositional change. This is the first place in a while where I wish the APXS and the Mossbauer were still working as quickly as they did a couple of years ago...

-the other Doug

Well, then, wouldn't it be somewhat disingenuous to claim that the MERs have only cost about $20 million a year? It would be nice if you could just ignore the initial nearly-billion-dollar expense and just claim costs since landing, but that's something of a misrepresentation.

Indeed, when you put all of the costs together, the MER project has thus far, when amortized out to present, cost well more than $120 million per year.

Of course, just speaking of *extension* costs of running each rover past its 90-sol design lifetime, yes, we're looking at a little more than $20 million a year, and I would bet that DSN costs account for a large majority of that. (I mean, look at it -- there are what, about 20 people working on the MER project at any given time right now, correct? If the project covers an average of $50K salary per person per year, that's a million dollars. Add amortization of their computer systems, rental of office and work space, travel expenses, etc., etc., you'd have to top out at about $2 million prior to DSN costs. So it would seem that the DSN costs alone for a year of operations run up to about $18 to $20 million per year.)

It's getting to be time to attack the real funding-drain of any and all deep space missions -- the astronomical (pun intended) fees being charged for communicating with the spacecraft.

-the other Doug

If it's a "baby" gully, it's been a baby for quite a while. The sand ripples evident in the image seem to have conformed to the dip into the linear depression. If this feature were a new gully that is just beginning to form, you wouldn't expect that there would have been time for such conformal ripples to have formed along the topography.

-the other Doug

US $20 million a year sounds a little low, Phil. Assuming we started spending money on the MER project in 2001, that comes out to a total of $160 million. I thought we had spent more than that by now...

Even if it your figure is low, we've still gotten one heck of a bargain for our investment, haven't we?

-the other Doug

If I lived in the EU, I'd nominate Stu. For someone not directly associated with ESA, he's done an incredible amount of outreach. He goes out and tries to infect children with the space exploration bug, and I think that's a sign of a Higher Calling...

-the other Doug

For anyone who has seen the musical The Fantasticks:

LUISA: Oh, my! That rover... it's stuck!

EL GALLO: The mask!

LUISA: But it can't move!

EL GALLO: The mask!

LUISA: It will never get to its next destination!

EL GALLO: Put on the mask!

(LUISA puts on the mask)

LUISA: Oh, look! It's a wonderful stationary lander! Look at the pretty pictures!



-the other Doug

Thanks! I've learned through long experience that when I assume that people have taken into account things that seem extremely obvious to me, and I never say anything, others invariably have missed the same realization. Of course, when I *do* mention these things, it ensures that someone has already considered it and is taking it into account...

-the other Doug

It's impossible to tell if the rock under the WEB is a relatively small rock that is "floating" on top of rather loose, unconsolidated dust, or whether it's the tip of a rockberg, so to speak. If it's the very top of a rock that's large enough to be firmly grounded, it is possible to put so much weight onto it that you reduce the effective weight on the wheels to the point where you'll never get any traction out of them.

Me, I think that rock will push down into the sand and not carry very much of Spirit's weight. But that's just a gut-level feeling; when looked at objectively, I doubt there's any way to know for sure except by going ahead with an extraction attempt and seeing what happens.

-the other Doug

It's a wonderful example of how observing affects the thing being observed.

I'm also just a tiny bit skeptical that you can vent the heat from the boat's warm interior (including waste heat from the ASRGs) up into the air and not have any effect on the temperature or composition of the fluid in which you're floating your boat. At the very least, you will heat a column of air over the boat that will cause chemical reactions in the liquids and gases suspended in the heated air column. Products of those reactions will tend to fall back out of the air column, and if they're heavy enough they'll land in the fluid. Most of this fallout would happen near the boat, I would think. So, anything your vented heat precipitates out of the "humid" air will then change the nature of the air and the fluids you're observing.

Also, what happens if the atmosphere over the lake contains an inversion layer that traps the "superheated" air close to the lake surface? We're talking about a rather thick atmosphere, here. Microclimates might well come into existence in such conditions that we don't know enough to model very well, and they could not only trap hot air for short periods, they would also be disrupted by hot, dry air, making our observations of them resemble Mike's burnt tree branch.

I just keep thinking, even if the heat released is relatively low by our standards (under 100 degrees C), the difference between that and the boiling point of the fluids they're in is much larger than you'd think. I'd imagine that if you applied the same degree of difference to, say, the boiling point of water, it would be something like trying to examine the ocean from a boat that's venting white-hot plasma at 5,000 degrees C. Your water collectors, designed to tell you all sorts of things about the chemistry and properties of the seawater, might just end up picking up a bunch of charred feathers and bird carcasses and leave you trying to understand how those fit in with your model of the oceanic environment...

-the other Doug

I would say that ground cracks that aren't filled up with dust occur because the process of dust deposition v. deflation has achieved a dynamic stability on Mars. The winds giveth, the winds taketh away...

-the other Doug

In re landing somewhere that you expect precipitation, I rather thought that the most likely precipitation seasons are winters at the poles -- places where there will be no light, and thus no possibility of pictures. (I don't care if all you get are pictures of a glass-smooth lake surface and the sky, imagery has proven over and over again to be extremely useful, even in places where you would never expect it to be. I won't be happy with a Titan lander, no matter where it's targeted, that has no ability to return images.)

Also, the boat will be an *awful* lot warmer than the boiling point of the liquid in which it's supposed to float. This isn't water, guys, and we're talking about landing a boat that runs on the waste heat from plutonium decay. Just how, exactly, do the designers propose to vent the heat from the probe in such a way that it doesn't transfer *any* of that heat into the liquid? We won't get information on anything like the liquid's natural state if our boat's major impact on its surroundings is to boil away the liquid in which it floats...

-the other Doug

According to our best models, Mars' axial tilt varies from its current 25 degrees to as little as 15 degrees and as much as 80 degrees. With an 80-degree tilt, it seems pretty obvious that the rotational poles will lose *all* of their residual ice caps and that polar conditions could exist almost all the way down to the equator.

So, for a significant fraction of the geologic history of Mars, areas that are not now subject to a polar climate were covered with dense caps of water and dry ice.

So... since we know (if our models are correct) that Mars *must* have huge areas that were once polar, what kinds of terrain alteration ought we be looking for as remnant indicators? If current polar geology is any guide, I'd think you would see surfaces covered over with the layered deposits that form as dust forms films between successive seasonal ice buildups.

What areas of Mars seem to be covered with such deposits? Do we have the kind of imaging we need to detect this kind of thing?

I will point out that Meridiani sure looks like it could be a candidate area...

-the other Doug

Mike, you're describing a lag deposit, of which we've seen quite a few examples on Mars (most significantly in the blueberry paving in the flatlands of Meridiani). When you have such a friable surface, these sulfate-rich rocks being very soft and crumbly, the stuff deflates pretty quickly over geologic time, and the surfaces achieve a dynamic stability when lag deposits become thick enough to armor the underlying surface.

And serpens, I'll note that BI seems to be sitting on one side of a ripple-like rise, tilted up and lifted off the ground on the far side of the ripple crest. Looks exactly as you describe -- a rock in the process of doing a gentle, eons-long rocking descent as the surface erodes out from under it.

In terms of Vail Beach itself, I can well imagine that the impact event could have crumbled off "flakes" (small pebbles) of a superheated meteor, which would end up embedded close to the main embedded meteor. Also, the thing would have been quite stressed and shatter-damaged (as much as a piece of nickel-iron can be shatter-damaged) from the time it created its crater through to the present day. I can well imagine subsequent weathering causing pebbles to break off.

Finally (here's the real wildcard), it *is* possible that Meridiani was at one time a polar environment, and BI impacted not into a rocky surface but into layers of water and dry ice. It was then subsequently dropped onto the surface after the polar ices had all sublimated away. That's one excellent way of explaining how a meteor can be deposited, as if by a gentle hand, onto the Martian surface (as we've seen in several places).

-the other Doug

Thanks for reminding me that you had referenced Middle Crescent, Kenny. Sorry I missed it!

As for the crater itself, I'm only impressed because the crater itself wasn't even named on half of the crew maps of the landing site, and IIRC was never referred to as Middle Crescent during conversations between the crew and Houston. Heck, due to the loss of the TV camera and subsequent lack of media coverage, there wasn't even much public awareness at the time that the crew made a short little geology walk after deploying the ALSEP.

I think you'd likely have to have pored over the ALSJ as much as I have to be familiar with the name Middle Crescent. IIRC, there's no real definitive source of the name, either -- just one set of maps that showed up one day that labeled three large craters arrayed in a crescent after their positions in the crescent. I don't recall off the top of my head if the other two were Upper and Lower or Right and Left or whatever, but that's generally what I recall. And again, this was on a somewhat larger-scale map than the map of the Snowman, to be used, I guess, if the crew landed significantly off-target.

Of course, these are all unofficial names, anyway. Am I right in thinking, Phil, that the names of the craters at the A12 site were never proposed to the IAU for official recognition?

-the other Doug

Now -- witness the *power* of this fully armed and operational battle station... er, space telescope!



-the other Doug

Ah, Phil... exquisite! And let me say, you're the only guy here I know of who would know to correctly identify Middle Crescent Crater.

Now what I'm really looking forward to is seeing how well we can see Rover tracks on Hadley Delta, Stone Mountain and the North and South Massifs, and whether or not we can see sets of footprint tracks at the sampling stations at Hadley, Descartes and Taurus-Littrow. (The instance we do have, of Station 6 from A17, doesn't show much in terms of tracks of any kind, a fact which I'm tempted to attribute to the sun angle.)

-the other Doug

Expectations are everything, centsworth. The village idiot being able to speak a complete sentence is either pathetic or triumphant, depending on your expectations...

-the other Doug

That is an extremely good question, one that still incites a certain amount of discussion (if not controversy).

We have a fairly good feel for the rate at which a rocky surface is "tilled" by impact into a soil-like regolith (a process that will literally form a thin layer of soil on the tops of rocks that sit on the surface long enough). And analysis of rocks and soil taken from the very surficial layer of the regolith for solar wind particles and irradiation gives us a pretty good idea of how long any given rock or soil layer has been on the surface.

At the mare locations, it appeared that most of the rocks had been on the surface anywhere from a few hundred thousand to a few hundred million years. The cleanest of the rocks, as you might expect, were the ones that had been on the surface the least amount of time. However, many more of the rocks collected at highland sites (Fra Mauro and Descartes) were dust covered as they sat on the ground than you found in the mare regions.

Now, the exposure (and sometimes creation, in the case of regolith breccia) of new rocks on the surface, their subsequent weathering and burial, and in many cases exhumation and re-exposure, is a process that exhibits itself in its every phase on every square kilometer of the lunar surface. Perhaps due to the much thicker layer of regolith, though, this process seems to deliver far fewer angular rocks to the surface in highland areas than it does in mare areas; perhaps this accounts for the difference in the dust covering on highland vs mare rocks.

In another vein, one of the theories I've heard for seeing clean rocks is that micrometeor bombardment "sandblasts" the surface rocks, literally blowing the rocks clean of dust accumulated due to any depositional process (impact or dust levitation). This theory is somewhat borne out by a close examination of lunar rocks, which exhibit "zap pits" on their exposed surfaces, tiny craters caused by micrometeor impacts. You would think, though, that this process would work equally well at highland as at mare sites (assuming the micrometeor impact rate would be the same at both), and yet you see more dust-covered rocks at highland sites. So, as I say, there is still discussion about the theory, mostly centering around compositional differences between the two types of terrains.

The other constructional effect of dust movement is the construction of fillets around sitting rocks. In general, fillets around lunar rocks tend to form around more rounded or sub-rounded rocks; you rarely saw fillets around angular rocks. This has been interpreted to mean that the fillets are being formed by the slow weathering of the sitting rock, the weathering being caused by long-duration exposure to the thermal, radiation and micrometeor environment. However -- and this is a big however -- in a few cases the regolith from the fillet tested out as significantly *older* than samples from the rock itself. This was explained by the admixture of other materials into the fillet soil, but that means that, at least in some cases, the fillets are being emplaced with material that didn't come from the rock the fillet contacts. The best current theory, of course, is that such admixtures come from impact transport of soil into the fillets. However, you don't tend to see any average orientation of fillets within a field of filleted rocks, unless the rocks are on a slope and it's obvious that the filleting is slope-controlled.

So, you see, there has been discussion of the phenomenon of clean rocks going on since Surveyor I showed us what the surface above a thin layer of regolith looks like. And discussion of related phenomena. It just seems that, instead of needing additional mechanisms to account for the amount of dust and soil we see on top of exposed rocks, we need to find a cleaning mechanism (that still is not clearly understood) to account for what we think ought to be deposited by impact processes alone. (I'm sure that there are more processes in play, to account for the things we've seen, than we yet know to apply to the question... )

I will point out that electrostatic dust levitation has the potential to remove dust from rocks. However, I would think it has the equal potential for re-deposition, so I can't conceive of a process that isn't a break-even... *sigh*...

-the other Doug

I figured it was time to begin a thread like this, especially since some of us may still be looking for the Surveyor III retro motor casing (assuming the bright dot to the north of the landing site isn't it).

We ought to be seeing some of the other Surveyors fairly soon, I would think. We know most of their locations pretty accurately. Again, I think there is a lot to be gained, both from scientific and engineering standpoints, from detailed imaging of the Surveyor VII landing site, just to mention one. And I really want to see how visible the Lunakhod tracks are as opposed to the MET and LRV tracks.

So... until we begin to see images of other unmanned hardware (or the craters caused by same), we could always discuss comparisons of Surveyor III surface imagery to the new LROC images of its landing site here. I'm especially taken by how you can resolve many of the blocks in Block Crater in the LROC image, which gives you a good feel for the explosive nature of the ejecta and roughly where in the ejecta plume a given block might have come from. Might be interesting/useful to apply this information to the samples taken at that location.

-the other Doug

The reason I say that the Apollo experiment results (including LEAM, which was designed to look for dust particles) didn't get conclusive results in re electrostatic dust levitation is that we are just now seeing anything substantive published on the subject. It has taken a more advanced fields and particles understanding of the lunar environment than we had at the time to eliminate various other hypotheses and determine that the observed results were due to electrostatic levitation. Besides, the kinds of fields and energetic particles thought to be required for dust levitation weren't particularly evident in other experimental results, in particular the SIDE and CPLEE results. (The exhaust from the Apollo rocket engines, for example, had a much more noticeable impact on the lunar environment than did the terminator effects that cause the dust levitation.)

Again -- we simply don't see the kind of global dust cover on the tops of rocks, etc. that we would if dust levitation over eons had significant erosional or constructional effects. At least, IMHO. The dust deposited on the tops of rocks is well accounted for by the amount of dust and debris flung about by impact events, and in fact is very minor considering the great amounts of time these rocks have been lying on the surface.

I think the best comparison would be to say that electrostatic dust levitation has probably had the same erosional and constructional impact on lunar geology as the infall of myriad tons of meteoric dust per day on Earth has had on terrestrial geology. Yes, there is a very minor though observable effect, but its overall effect is by far overwhelmed by early orogenic and continuing impact processes.

-the other Doug

I find it interesting that one of the Lunar Orbiters had a similar issue with overheating, and IIRC it wasn't the first LO to be flown. Again IIRC, ground controllers had to change the spacecraft state, opening or closing a thermal door to manage heat within the vehicle even though this had an effect on the usability of the camera system.

So, while I'm sure there is enough blame to go around in any situation like this, I think it's also important to note that the Big Boys, the people who did this kind of thing for the first time a couple of generations ago, ran into similar problems even after they thought they knew what the environment was like. So, cut the ISRO people a little slack... This is an excellent learning opportunity that will make their follow-on missions even better.

-the other Doug

Honestly, the effect of electrostatic suspension and movement of dust in the lunar environment is just barely detectable in empirical measurements taken during Apollo. It's way down in the noise on experiments that were designed to notice movement of gases and of charged particles, which ought to have seen it clearly were it an effect large enough to have an impact on lunar geology.

Put it this way -- on the maria, there are a lot of rocks that are dust-free, that have been lying on the surface for hundreds of millions of years. Heck, there are even ancient rocks in the highlands that are relatively dust-free. From what we saw when we went there, I'd have to say that impact scattering of dust is a far more substantial effect in the lunar environment than electrostatic dust levitation has ever been.

-the other Doug

Nice work, PDP! In particular, the A14 image really shows the contours of the old, extremely subdued crater that Antares landed in. It's also obvious that all of the Triplet craters, even the subdued-itself North Triplet, are an awful lot younger than the old, extremely subdued craters, as North is directly superposed on the landing site crater's northeast rim.

-the other Doug

Just to be completely clear -- I think we should stop referring to a "tank," as it seems some people are envisioning tankage that fed liquid propellants into a combustion chamber complete with attached nozzle extension.

The Surveyor main retro motor was a solid rocket motor. It was a sphere a little less than a meter in diameter that was filled with between 1,200 and 1,300 pounds of solid propellant. A star-shaped core opened out to a throat and nozzle that, when the spacecraft was properly aligned, faced into the velocity vector. Ignition charges would ignite the fuel down into the core, the fuel burns from the core out to the casing, and the rest is a simple application of the Rocket Principle.

While the motor is a "pressure vessel" in the same way that any SRBs are pressure vessels (they must contain the pressure of the expanding gases as the solid fuel burns), it's not what comes to my mind when I think of a pressure vessel. My conception of a pressure vessel is a tank that holds a liquid at pressure. (After all, other SRBs are referred to as "motors" when filled and "casings" when empty, but never referred to as "tanks"...)

It's hard to say how much impact force a burned-out solid rocket motor casing, with only a few pounds of fuel left inside, could withstand without pancaking. But the assembly did have a big open throat when it impacted, and was vented to vacuum inside and out, so we'd only be talking about the inherent tensile strength of the metal and the welds after they had been heated dramatically by the burning of the fuel and been stressed by containing the pressure of the burning fuel (in all directions except through the nozzle, of course). It would not have the same kind of resistance to pancaking that a pressurized tank would have.

-the other Doug

p.s. -- no, Ilbasso, the mock-up you have pictured doesn't include the retro motor. The motor nestled in a cavity exactly in the middle of the landing legs. The sphere extended below the plane of the footpads, and the nozzle, of course, extended even further down than that. Any Surveyor model you see that doesn't have a big sphere sticking out like a potbelly from between its legs doesn't include the retro motor. DVD

Here's a thought -- Europa's surface is mostly water ice, right? Ice is an excellent radiation shield, right? And we need to learn how to melt our way down into the ocean below somehow, right?

You could greatly increase the lifetime of a Europa lander if you could effectively bury most of it in ice soon after it lands...

-the other Doug