I've been able to listen for a bit, here (though I was on the phone with my girlfriend for the first 10 minutes or so). What I got out of Squyres' discussion is that the *only* primary science goal that has been identified for the foray into the crater is the investigation of the "bright band" of evaporite visible in the crater walls. They *think* that this band is contiguous to the layering found in Endurance, and they want to look at compositions (particularly the leeching of certain salts at given depths) to try and both confirm that these layers were laid down at the same time as the layers in Endurance, and to determine if the same processes that leeched some salts at Endurance were also working here, several km away.

They're not saying that once the bright band is explored we'll up and leave VC. Just that this is the primary mission of the foray into the crater. Squyres made it sound like he's certain we'll see other things we want to check out once we get down into the thing.

Now we're hearing a litany of all the things that have broken on the rover since we left Endurance... and commentary on how we had to spend six months looking at the crater to decide that the best place to enter is where we started out...

-the other Doug

Bringing up the question, how many MERs can dance on the head of a pin?

The real issue of extension costs, in my mind, is the cost of DSN time. If you can cut down your support staff here on Earth to minimum levels and just be taking repetitive images and passive data, you do cut your costs down some. But at several thousand dollars per hour of DSN time, the cost of just getting your data back to Earth runs into the millions of dollars a year, even with passive, nearly dead rovers.

There is a lot of focus on reducing the cost per pound to get spacecraft into LEO and beyond. I think there needs to be a similar effort to reduce the cost of communicating with your spacecraft once they leave LEO, or else you'll continue to see probes which have a lot of life left in them abandoned due to the costs of keeping in regular contact with them.

-the other Doug

Remember, too, that we're not just talking about a pretty straight-line graph in which the amount of dust entrained in the atmosphere relates directly to the amount of dust deposited on any given surface. There are a lot of microclimatological effects right along the surface that greatly impact dust deposition rates. If we were to park Spirit on top of El Dorado for a winter, for example (and I know, it would never happen, it faces the wrong way, etc.), you'd likely never survive because the hills force a turbulence that drops dust out of the air selectively onto the El Dorado formation.

IMHO, Spirit spent last winter in a place that tends to collect a little more dust than other places within reach. If she can claw her way up the side of a hill that faces into the prevailing winter winds, as opposed to sitting in a "deposition sink," she might have a better shot at surviving her next winter. But if she stays exclusively in the Home Plate area and doesn't get very far from it, the deposition rate may be just high enough to kill her without an extraordinarily vigorous cleaning event just before the onset of winter.

-the other Doug

If Mars had developed salty oceans before the late heavy bombardment nearly 4 billion years ago, that might explain the amount of salt that is distributed all across the planet. Impact cratering is generally not thought to be a great horizontal mixer of material, mixing more vertically than horizontally (at least based on the lessons learned from the Moon), but the very magnitude of the LHB could have distributed salts from the bottoms of obliterated southern hemisphere salty seas all across the planet (especially considering how far-flung the LHB must have thrown salty water from these putative seas into the early Martian atmosphere).

I can also picture a Mars which has quickly lost much of its atmosphere after the magnetic field died, cooling drastically, losing much of its liquid water to evaporation and ice sublimation and exposing tens of thousands of square kilometers of salty seabed; winds may then have eroded these salt flats and distributed the salts across the planet. So you don't necessarily need the LHB to explain the ubiquity of salts on Mars without requiring the entire planet to have been covered with salty seas, but it remains one plausible transport mechanism.

If there was a Great Northern Ocean, I'm thinking it must have post-dated the LHB, since there is no reason to believe that the impact flux would have limited itself to the southern hemisphere. I truly believe that, at the end of the LHB, Mars looked pretty much like the southern hemisphere looks today, but all over. The smoothed terrains we see in the north must have been overlain over a rough lunar-highlands-type of terrain, unless you want to try and explain how such a heavy bombardment could have completely missed one whole hemisphere of the planet... (Just trying to apply Occam's Razor, here.)

Nonetheless, it's important to remember that Mars with a thicker atmosphere and any kind of greenhouse effect would have been considerably warmer than it is today -- if you moved the Earth to Mars' orbit, it would be somewhat cooler but generally habitable (our seas and oceans wouldn't all freeze over, etc.). It's a touch disingenuous to suggest that Mars could never have been warm and wet because of its distance from the Sun and the related lower insolation than that received here on Earth. Mars is cold and dry today primarily because it lacks a magnetic field and thus the solar wind has sputtered a major percentage of its original volatiles right off of it. Had Mars not lost its magnetic field early on, it might still be warm enough and have enough atmosphere to support liquid water on the surface.

-the other Doug

True. But atmospheric science isn't the same as meteorology, or as it was described, a "weather station." It's a fine line, I know. But for telling us anything about the actual weather at a MER location, all of the rovers' instrumentation is, IMHO, less valuable than would have been a stick with a small windsock (or just pieces of yarn) attached to it.

There is a point at which you have to decide if the salaries, DSN time, and managerial overhead for which you have to pay as long as the MERs are kept alive are justified by the amount of new and unique data you can get. Yes, you can get some interesting data about the air column above the MERs from mini-TES, and you can get some rather averaged air composition data from the APXS. Is that worth expenditures of several million dollars per extension for an otherwise immobile and mined-out (i.e., local field as minutely examined as possible) MER?

As long as the near field can be changed (i.e., as long as a MER is mobile), it's a no-brainer. You'd continue to extend the mission, even if you were to completely lose an IDD or even mini-TES. But once you can no longer move, I'd be surprised if the mission would be extended once an "endgame" plan for maximizing return from your final location was completed.

-the other Doug

Yes, many of the engineers and scientists, as well as managers, who were with the MER project from the beginning have moved on to other projects. Some are working on Phoenix, some on MSL, and others are working on other mission proposals. Some (though a very few, I imagine) are working somewhere else entirely, not in the planetary probe business.

It's like any organization that operates for more than a short period -- you get turnover. Some people leave to pursue other interests, some are recruited into projects where their expertise is needed, and some (like the Entry, Descent Landing, or EDL, team) find their jobs at an end once a given mission phase is completed. For example, Rob Manning was one of the key engineers on the Pathfinder and MER EDL teams. Rob has been working on MSL's landing system for a couple of years now, and has been kind enough to keep all of us here at UMSF up to date on their progress... But once both MERs were safely landed on Mars, Rob and others on the EDL team were freed up to pursue other projects.

-the other Doug

Unfortunately, the MERs are drastically under-equipped to serve as meteorological stations. They have no instrumentation for directly analyzing winds, pressures and temperatures. The only instruments that can capture weather data are the cameras, and while you can take cool images of dust devils and boring images of the Sun to measure tau, I'm not sure we'd see mission extensions solely for those purposes once an immobile rover's near field has been examined as carefully as possible.

-the other Doug

Yep -- I see what you're talking about. I have a little wonderment as to how much shock alteration might play a part in the interruption of layers within any of these blocks, but I certainly see cross-bedding in many of the rocks in the cliff face. And there are a few examples of the cross-bedding that the MER team has called festoons, yes.

-the other Doug

Or, more specifically, what was the greatest tau value recorded by the Viking landers when they endured major global dust storms? Each went through at least two major dust storms, and I know that *some* estimate of tau during those periods has been made.

Also, I know I've seen sequences of Viking lander images showing dust buildup after dust storms. I'd be interested in seeing those again, to get a feel for the kind of short-term buildup we may be looking at for our rovers.

-the other Doug

Well, isn't it almost a truism that semi-global and global dust storms on Mars tend to occur as the planet approaches and works through its equinoces? Those are the times when the most extensive atmospheric transfer between the poles occurs (as CO2 sublimates off the cap approaching summer and condenses onto the cap approaching winter), and so generates the greatest global winds.

We've survived regional storms since the MERs landed, we can only hope that this storm (and any others that may pop up over the next couple of months) will remain regional and not go semi-global or global. We could still see both rovers die within days of each other if a global dust storm of the extent, say, of the 1971 storm were to develop.

Do note, though, that the rovers might well become cleaned by the more energetic winds to an extent that they *could* survive even a major dust storm. The HiRISE color image of the Viking 1 lander, for example, demonstrates that it is still primarily non-dust-covered, and we know it has endured several global dust storms. Depending on the rate of deposition vs. the rate of cleaning during such a storm, we might be able to get the rovers to advantageous slopes and weather a storm, as we have weathered Martian winters.

-the other Doug

No, no, no, Ted -- what we really need is Deep Rap - Triton, in which a huge *knuckle* is sent to Neptune's largest moon and used to rap on the rind. Extremely sensitive microphones aboard the flyby craft will then listen for the "exact right thunking sound" to determine the ripeness of the interior...



-the other Doug

In discussion of the blueberries, I fail to see how they could be accretionary lapilli (or anything similar) from within a surge cloud and also exhibit the dimple/stalk morphology that we see in many/most of them. I can see stalks forming if they are concretions that built up from small voids in the salty rocks, not in lapilli.

And we don't see them *ever* deforming the layers in which they appear, as you would imagine they would if they fell onto newly-formed layers in the salty rocks. They are embedded in a fashion which screams (to my eye) "concretions formed in place" and not "lapilli that fell onto these layers." They are not organized along specific layers, they are scattered like shotgun-shot all throughout the layered rocks. If they were lapilli that were just dropped onto the still-fragmented salt dust that was being deposited by a surge, you would also expect a *lot* of signs of turbulence in the layer deposition "downwind" (or "downsurge") of the blueberries, and we don't. We see them perfectly embedded in layers that are otherwise laid down quite flat. And if we also buy the theory that each millimeter-thick layer was laid down by a separate impact surge event (which I still have a hard time believing, since the layers are so uniform in thickness), and we know that the blueberries are significantly larger in diameter than the layers in which they are embedded, where is the turbulence we should see "downsurge" from blueberries emplaced by the last surge? I would expect fillets along the upsurge side of the berries, and hollows on the downsurge side, even if the surge flow was relatively slow and non-violent. We see absolutely no sign of this.

I wonder a bit, too, about the lack of shales being definitive proof against a watery environment. The Meridiani light-toned unit is very thick -- if there were simply not enough silicates (especially phyllosilicates) to form a significant amount of the depositional surface, we'd be looking at a large substrate which simply doesn't contain the constructional materials necessary to form impermeable floors (i.e., shales) for standing water. In which case, you'd be looking at standing water *only* when the water table exceeded the level of the surface. As the water table receded downward, it would simply flow through a unit of permeable salty rock all the way down to the base of the aquifer, which (in my thinking) would consist of clays or shales formed at the top of the unit that lies below the light-toned unit. Since *none* of that unit is exhumed anywhere that Oppy has visited, we can't judge on the lack of such materials on the top of the present surface.

Just because Mars may once have had liquid water doesn't mean it would necessarily have formed the same features such water might have created on Earth (like pervasive shales), especially if there are compositional differences in the materials that held the water. Conditions on a hypothetical "wet, warm" Mars would have been very different from conditions on a wet, warm (and teeming-with-life) Earth -- we always need to appreciate that the same water conditions on the two planets could result in some significantly different results when it comes to how rocks were created and altered.

Just my $.02...

-the other Doug

Most craters aren't parabolic, and thus don't have perfect heat-focusing characteristics. But they do, indeed, heat the air above them and create thermals. If you don't believe me, look at the dust devil tracks in Gusev -- they very frequently spin out of craters.

You have to wonder why you see dust devils forming at Gusev and not spinning out of Victoria, here. I imagine there are a lot of factors, but still -- it is odd that some craters spawn dust devils and others don't. None of the craters at Meridiani seem to be spawning DDs, and yet lots of them are formed at Gusev.

-the other Doug

Just try adding more stars... you get some really interesting orbits when you have three or more gravity sources in the mix.

I placed three stars in a rough triangle, and found that I couldn't get a trajectory on any object that didn't impact one of the stars after only a few orbits. The planets tended to shoot up from one of the stars and then head in on a death-dive into one of the other ones.

-the other Doug

OK, well -- it wouldn't be much of an improvement over Mars Science Lander, but we could always call it Mars Gravity Probe 1...

(10 points for anyone who can identify where *that* reference comes from... )

-the other Doug

Yes, it generally is true. It's a matter of sunlight reflecting off the crater walls. If you look at THEMIS images from Mars Odyssey, you can see that craters tend to be warmer than the surrounding terrain, especially just after sunset.

-the other Doug

Ah, but if you were to name MSL the Hannibal 8, after it went about 90 meters the engine would fall out!

"Push the button, Max!"

-the other Doug

p.s. -- if MSL finds Natalie Wood wearing a merry widow, though, just *think* what that could do for Mars exploration funding!

Well -- the older tracks have definitely been softened (presumably by aeolian erosion) in the time since they were laid down.

I'm thinking that in less than a decade, the only way you'll be able to see these tracks at all is by the fact that the concretions have been pressed down into the soil and thus won't be as exposed. The tracks will look like dusty lines to the naked eye, but will still be quite discernible in the right spectra (i.e., lacking any trace of a hematite signature).

-the other Doug

Well, heck -- if we're talking about a rolling robot with a death ray that can't roll as fast as people run away from it, might as well go all the way and name the thing "Dalek."



-the other Doug

I know -- same here. And the physical effects found at the site all indicate an airburst-type explosion.

Now, one other airburst explosion that we know of has occurred since Tunguska, though it was a much, much smaller bolide that exploded. I'm referring to the Tagish Lake meteor. That meteor did scatter a lot of material on the ground (well, specifically on the surface of a frozen lake) below the airburst. So we have evidence that such airburst-style bolide impacts don't vaporize the entire impactor as they explode.

Perhaps the Tunguska impactor exploded in the air but some of the mass survived the airburst and struck the ground. That impact would have occurred along the ballistic trajectory of the impactor and not in the center of the airburst-generated blast zone, so it would make sense for it to be somewhat offset from the center of that blast zone. Which is supposedly what is being claimed here.

We just don't have a very good concept of how various types of impactors behave under extreme entry heating conditions. We know generally what can happen from looking at the few such events that have occurred on Earth during human history, and looking at the resulting impact effects of even older bolide strikes. But we don't know the exact composition of the various impactors that have been observed; we have a very poor idea of the composition of airburst impactors, especially. I can well imagine that impactors relatively enriched in volatiles would be more likely to explode before they hit the ground, but we don't know how such bodies are organized before they hit our atmosphere. So, if a large cometary fragment should strike us, it's possible that the volatiles would be irregularly distributed within the mass and while a portion of the mass might explode in the air, another portion might be less enriched in volatiles and thus continue on to a ground impact.

We just don't have enough data to be able to model that kind of thing. Yet.

-the other Doug

Yes, that answers a lot of my questions -- thanks! I guess one thing I was wondering was whether a dozen, or a hundred, little (like half- to one-meter) dishes on the ground could be used in a sort of an "antenna farm" mode to simulate a 70m or larger receiving antenna.

You see, there are literally hundreds of thousands of people here in the U.S. who have at one time or another used a satellite cable system (like Dish Network) but who no longer use that service. That's a lot of parabolic dish receiving antennas that are just going to waste.

If all of those unused dishes were mounted with decent views of the ecliptic (where most of the unmanned probes spend their lives) and tracking mounts, and set to communicate to a central data collection center, we could have a "distributed" DSN network made up of thousands of dishes. And heck -- some of them could be tracking Venus, some Mars, some Mercury, and some Saturn. And some tracking points in between.

I know it's probably a foolish pipe dream, but it would seem that you could vastly expand the DSN (within North America, at least) at relatively little overall cost (certainly at relatively little cost per dish) by making use of these unused dishes.

Your response tells me that such a network of dishes could be useful for getting additional science out of the assets we have in place around the Solar System. That's the information I was looking for. Now all we have to do is find the seed money for outfitting these unused little dishes, and we can get started...

-the other Doug

You really think UMSF use of RTGs, et al, has been successful and uneventful enough to push them off the anti-nuke crowd's radars? I will remind you that, in their last gasp at trying to look important to themselves, these same people INSISTED that Cassini be crashed in Saturn upon arrival instead of placed into orbit, since (they insisted) anything else meant that Cassini would eventually return to near-Earth space and pose a COMPLETELY UNACCEPTABLE RISK of a collision.

I'm not kidding.

-the other Doug

I'm glad I could confuse you even moreso than before, Mark...

-the other DOUG ()

Stu, just move here to Minneapolis, MN, USA. We get NASA-TV on our cable system. Full digital TV resolution (though not HD).

I love my cable system!

-the other Doug

Interesting speculation, Mike. I see your point about the similarities between the Xanadu/Fensal-Quivra-Azltan construct and Mars' Tharsis bulge.

However -- just how efficiently could Titan shift its orientation when locked into a tidal resonance with Saturn? Mars spins very fast, relatively speaking, and has a whole lot more rotational energy with which to shift the entire planet onto its side (so to speak). Titan, in contrast, spins very slowly on its axis and has the very deep Saturnian gravity well to deal with. I'd almost believe that tidal attraction from Saturn would supply more energy to such a process than Titan's own rotational energy could provide.

If Titan's mass was redistributed in a manner similar to what happened on Mars, I'd be willing to bet you'd see the thing reach an equilibrium with the "heaviest" part of the mass tidally locked, facing Saturn. Is that what we're seeing here? If not, I have to wonder a bit as to how the mechanism would work...

-the other Doug