OK -- here are two points that might possibly lead to further discussion. Here's hoping.

First point: If this hematite didn't form within the rocks, but is low-temperature hematite, then how did it form? Perhaps it formed some distance away from where it is now and was transported to its present location. And since 1) hematite can be produced from olivine-rich lavas and 2) there is a lot of olivine in unaltered Martian lavas, it's conceivable that low-temperature water processes could have formed this hematite -- just not in situ.

Second point: I know I've read that hematite, once formed, does not melt. If a hematitic bed of rock (formed in whatever climate and under whatever conditions were conducive to such formation) was struck by an energetic meteor (or even a basin-forming event), that hematitic rock bed wouldn't melt, it would be pulverized. Broken into pieces, smallest (dust-sized grains) nearest the impact point and larger away from the impact. Thus, it would be possible for an impact to distribute hematitic fragments within its ejecta blanket. (However, since the hematite would not melt, it would likely not accrete into spherules out of dust-sized granules within the ejecta cloud/surge. I can't imagine anything other than melting that would form the hard, solid berries we see out of hematitic particles and dust, and as has been said, hematite won't melt and therefore can't be annealed into a single solid mass from pulverized particles. And these berries are strong and erosion-resistant, they don't appear to be hematitic dust bound in some other kind of matrix.)

I am not siding with an impact origin for the spherules at this point. I need a lot more convincing before I will go that far. However, I believe there *is* a not-altogether-impossible sequence of events which which would allow for it. For the distribution to be so widespread in this area, multiple large impacts would have had to occurred into hematitic rock beds nearby the area. If the layered sulphates actually were laid down on top of berries as they sat on the surface (a process I just don't see evidence of in the MIs of embedded berries), then it is just possible that repeated impacts over time have excavated hematite, spherized the ejected granules either due to impact stresses or due to extreme erosive conditions within the impact cloud/surge, and covered the surface evenly enough and regularly enough for it to *appear* that they are uniformly distributed throughout the rock.

However, it just doesn't look like there are berry "deposition planes" within the rocks that would define the surfaces upon which they were deposited. Unless the putative impacts which distributed the berries (all at different distances and releasing different amounts of energy, thus excavating different amounts of rock and ejecting it different distances) somehow produce unformly-sized spherized pebbles each and every time, which I consider highly improbable, then I'm afraid our friend Occam won't approve.

The only thing that would make any sense whatsoever, if the berries are ejecta, is that they were ejected from a basin-forming impact partway across the planet. A single large impact event could create zones of ejecta of similar content and character that are hundreds to thousands of miles in extent, in one dimension or another. But again -- if the berries all came from a single huge impact, how did they get so uniformly distributed through the Meridiani sulphate-rich rock beds?

-the other Doug

I may be misremembering, but I have this vagrant memory that, at one point, they were referred to by the mission name Mariner Outer Planets Explorer. I also have a vagrant memory that they were renamed quickly after that, since no one wanted to fly a MOPE...

-the other Doug

I've been giving this matter quite a bit of thought, actually. I don't necessarily see the apparent very-high paleoimpact rate at Saturn as being indicative of a heavy bombardment that was greater than what was seen in the inner system -- I see it as a set of markers for an intense gravitational disruption that occurred in the outer system early in its history.

If you look at the moons of all of the three outer giant planets, you see objects that have literally been ripped apart and formed into rings, objects that came close to being ripped apart and still show the aftermath of being tremendously stressed, and objects that were ripped apart and then re-formed into intact (if savaged) moons.

Yes, I think it's possible to postulate that all of these effects were caused simply by impacts, and if your model doesn't include the possibility of intense gravitational gradients, impacts fit Occam's Razor quite well. But recall that, according to "best" theories right now, Jupiter formed farther out than Saturn and migrated inwards to its current location. Jupiter is one huge mother, with the second-largest gravitational field in the system. I think, if the theory of its migration is sound, that we're seeing effects from gravitational shear that occurred as Jupiter migrated.

One of the things that tends to support this perspective, for me, is that Jupiter's own moons show the *least* of these observed effects. Since they were very close to Jupiter and their orbits were so dominated by the immense Jovian gravitational field, you would expect them to suffer the fewest effects. Et voila, that's what we observe.

You can also postulate that Jupiter's migration wasn't entirely responsible for all of the effects we see -- our system formed within the debris cloud of a supernova explosion, after all, it's unreasnable to assume that there were no other large masses (from stars-in-formation to objects the size of several Jupiters) being accreted nearby out of the same cloud. Any number of close encounters with such masses could also account for the disruptions we see.

Truly, I think we're looking not at an impact cataclysm, but at a gravitational one.

-the other Doug

This statement, if it is a currently accepted postulate for how planar beds are formed during basal surges, is quite well-suited for testing in re the Meridiani deposits.

It predicts that, for each surge event, you should see inversely graded planar beds. In other words, the largest grains should make up the first beds deposited, followed by progressively smaller grains until the uppermost layers are made up of the finest grains. (At least, that's my reading of what "inversely graded" means.)

Has Oppy found such an inverse grading relationship between the beds in the units it has been able to study? Since the theory above uses as a basic theorem that the layering is entirely due to different grain sizes sorting out, there ought to be an observable change in grain sizes from layer to layer. Even if this delta is so small as to be difficult to measure from one layer to another, it ought to have been enough over the depth of the unit observed within Endurance to be able to be quantifiably observed.

So -- here's a direct test of your theory, Herr Doktor. It's even a test on which you can do a little non-rigorous work using the raw JPG images from back during the Endurance campaign (or more rigorous work using the images already released to the PDS). I have to say, I truly think that if anything of this sort had been observed at the time, we would have heard about it... but I'm prepared to be proven wrong on that if you want to try and pursue this proof.

-the other Doug

I was online when MPF landed -- that is to say, I had a *very* old PC (10/25 MHz switchable 488 processor, 100 MB hard drive, which was already 7 years old by then) that was barely able to run AOL 2.5. I downloaded each new image and drooled over them; for the first time in 20 years, I was looking at new images from Mars!

I was also having my very first dating relationship with a woman whom I met on the internet. I had been married and dated quite a bit before that, but this was new, meeting people on the internet. Since then, I've mostly dated women I've met online, but then it was something quite new. And that was the year the company for which I was consulting sent me on trips to England, Holland, Belgium, Argentina, Japan, the Philippines and Singapore. So the spring and summer of 1997 have a lot of good memories for me...


Better battery technology. The MERs were given batteries rated for something like 4,000 charge/discharge cycles under Martian thermal conditions, while MPF had batteries rated for something like 40 charge/discharge cycles.

-the other Doug

Just one last comment on the relative softness of the rocks on Mars:

There is one other measure of the hardness of the rocks that hasn't yet been mentioned. The RAT on Spirit wore out considerably faster than has the RAT on Opportunity. The RAT cutting edges were identical on MER-A and MER-B, so there is a quantifiable and measurable amount by which the rocks at Gusev are harder than the rocks at Meridiani. (I believe some estimate of Mohs scale was made for the various rocks that have been RATted, based on the amount of electrical power required to make the observed cuts. I don't know where I read that, though, and so I can only offer it as a piece of potential apocrypha.)

My own take on it is that the Meridiani rocks are probably pretty friable when you apply pressure cross-layer. But the way those layers have cemented give the rocks a fairly decent load-bearing strength when you apply pressure along a layer's plane. In other words, it's like plywood -- you can easily crumble off the edges, but sit on a slab of it and it won't tend so much to crack and crumble. Or, to sound like I know more than I do, the material's axis of greatest strength is planar and alined with the layers...

The very few surviving blocks of ejecta made of this material show preferential erosion cross-layer, as well. An ejecta block with a flat, contiguous layer for much of an exposed face appears to erode selectively along its non-planar faces. This would tend to support that the material is stronger (i.e., more erosion-resistant) when force is applied perpendicular to the plane. However, the rather noticeable lack of extant ejecta blocks from this material, as well as the "ground-down" condition of what now look like flat pavement slabs at various places in this unit, also speaks to material that is soft and relatively easily eroded.

-the other Doug

I'm actually a little more worried about Spirit than I am about Oppy. This dust is all still entrained in the atmosphere, it hasn't really started to fall out yet. I don't know why, but I have this gut feeling that Meridiani may collect less dust from this storm than Gusev eventually will. Maybe because there is less overall dust accumulation on the ground at Meridiani than there is at Gusev; it just feels like Meridiani doesn't collect dust as effectively as Gusev does. (Maybe Gusev's crater rim causes a large-scale swirl in the winds that tends to make dust collect within, while the lack of any such circulation patterns at Meridiani keeps it from getting dumped on nearly as much.)

I guess I'm thinking that the dust ought to have specific patterns of fallout, based on when in the year the storms occur and what the wind patterns are like at the time. It also may have something to do with your distance from where the storms start and how they grow. It just feels like, since Oppy was closer to this storm as it formed, it may actually get away with having less of the dust dumped on it than other places on the planet -- perhaps even halfway across the globe.

Also, rather obviously, the polar caps display a process in which dust is often sandwiched between layers of dry ice. It may well be that a majority of the dust pulled up during these major storms ends up being deposited at the fall/winter pole, to which the air is flowing and where the air is precipitating out and plating itself onto the ground. That would tend to make sense from a global circulation pattern perspective.

-the other Doug

The problem with positing a series of heavy bombardments, dating up until fairly recent times, is that we don't see a record for such a bombardment on Earth or Luna. While it is possible, I suppose, for bombardments to be set into motion that only affect a certain portion of the local neighborhood, I'd imagine that a heavy bombardment which would affect Mars would also affect Earth/Luna, and probably Venus and Mercury as well.

There have indeed been models put forth to explain the LHB in terms of migration of major outer planets -- the one I can remember best suggests that Jupiter originally formed farther from the Sun than Saturn did, and that as it migrated closer to our star it tossed Saturn further out and disrupted whatever rocky body (or bodies) occupied the orbital neighborhood that now lies between Mars and Jupiter. This disruption caused a great deal of the mass located in what is now the Asteroid Belt to fall towards the inner system... and smash into any inner rocky planet or moon that stood in its path.

Yes, there could have been other less major disruptions that could have caused a lot of the debris in the current Asteroid Belt to have meandered in towards Mars' orbit. But even without detailed mathematical calculations, my gut feeling is that anything that would have caused a major bombardment on Mars should also extend itself in towards the rest of the inner system. And the problem with that is that the most recent of Luna's large craters seems to be on the order of 100 million years, and those are very scarce. The shoulder-to-shoulder large crater structures on Luna are all of an age, and that age is somewhere around 3by ago.

Remember, the LHB resurfaced much of Luna, and from the looks of it, resurfaced much of Mars, as well. The same thing happened on Earth, of course, but Terra has effectively resurfaced itself many times since then and the crater remnants of the LHB are almost all gone by now.

I just don't see any way for a major disruption to pull enough mass in towards Mars to create a major bombardment and yet not toss enough of that mass in to the inner system to leave a record on Luna. I guess I'd say it's possible but extremely unlikely.

-the other Doug

Literally!

-the other Doug

Yes, but... the rocks at Gusev are all dense basalts (as can be observed empirically and also inferred from dozens of different sensor measurements), and *they* have also been carved by the wind, like a knife through butter.

Doesn't matter how hard the rocks are or how thin the air is -- if you blow on rocks with wind for long enough, you get aeolian erosion. Doesn't matter how dense or light the rocks are.

-the other Doug

Now, here's a question: did MPL have a descent imager and did it route its data through the same board as Phoenix is now arranged? I get the feeling from what is being said that this arrangement has been in place since the Surveyor 2001 configuration, and I know that configuration was very similar to the MPL configuration...

-the other Doug

Well, it depends... the PIs have to get their results published before they can come home, after all...

-the other Doug

Such a mission has a lot to be said for it. For one thing, it's easier to send a lot of lab equipment to, say, Phobos than to the surface of Mars, and it's likely cheaper (in terms of energy) to get the mass of the equipment you want to use to study Mars rocks to Phobos than it is to bring the rocks all the way back to Earth.

So, you set up a manned microgravity habitat on/in Phobos, outfit it with the best analysis tools you can easily get out there, and send down small sample return probes that bring you up a few kg of carefully selected rocks and soils every few months. Your PIs live on Phobos and send the detailed data back to colleagues on Earth.

What would be the minimum lab requirements for a Phobos geological analysis base? You'd want to have fine-scale composition and isotope analysis, as well as the best rock dating equipment you can afford to transport. You'd also want equipment for examining micro-fossils (just in case) and for examining ices and such for possible biological activity or remnants.

What suite of instruments would best serve your purposes in such a set-up? What are their power requirements? And how much of it can be feasibly transported via rocket from Earth to Phobos? Those are the questions I'd be asking right now...

-the other Doug

The answer is sort of "all of the above." The factors that contribute to a bolide explosion include:

Angle of Attack: A shallow entry allows for a lot more heating time. A more direct trajectory straight towards the ground creates a higher heating pulse, but for a far shorter amount of time. On a steep-angle trajectory, the impactor reaches the ground very quickly after encountering the upper atmosphere and is usually still "frozen" in the middle when it strikes. But shallow-angle impactors have time to heat through far more effectively, even though the peak heat pulse is less.

Composition: It's likely that only bodies containing volatiles will actually explode dramatically in the air prior to impact. A large stony body will simply ablate as you suggest. No matter how long it is heated, the worst that will happen to such a stony body is that it will come apart at maximum heat load and/or aerodynamic stress. Such a break-up can look a little like an explosion, but the energy is all kinetic. If the impactor is a cometary fragment, however, with frozen volatiles within, those volatiles can heat up as the bolide travels through the atmosphere. Let's say a lot of the impactor is made up of methane ices and clathrates -- and in the lower atmosphere, the body begins to break up as hundreds of tons of now-flammable methane and other hydrocarbon products are released into a white-hot plasma trail surrounded by fire-feeding oxygen. It goes kablooey... As evidence, we have the Tagish Lake meteor fragments, which are some of the few examples of what (we think) is a cometary fragment that have been recovered (the pieces were actually fine-grained clays, not stone or metals like most meteorites). Not coincidentally, the Tagish Lake body exploded in mid-air.

Speed: This isn't as important of a factor, in that a shallow entry angle will usually slow a bolide to relatively slow speeds by the time it heats enough to explode. But a higher-energy entry will actually be less likely to cause an explosion in that it can reduce the heating time, as compared to the heating time endured by a slower impactor traveling along the same trajectory. A lot of this depends on whether the body's vacuum perigee is a positive or negative number at the time it hits the upper atmosphere.

Now, I'm not a meteorite expert, but I play one on the Internet... However, I think I have the basics correct, here.

-the other Doug

I was just thumbing through Squyres' "Roving Mars" again recently, and ran across something that I had thought I remembered.

For quite a good time (several weeks), Steve himself kept holding on to the notion that the layered rocks in the walls of Eagle crater were some type of welded tuff. As I understand it, Don is basically proposing that these rocks are, in fact, a form of welded tuff.

The vugs and especially the formation of concretions within the rock layers (as opposed to disturbing or displacing the rock layers) were the factors that changed Squyres' mind. That and the fact that the blueberries were of rather different composition (i.e., hematitic) than the rock in which they were embedded; the question that begs an answer is why *any* basal surge (volcanic or impact) would deposit simultaneously two populations of materials, each very different from the other. The compositional differences were sort of the nail in the coffin as far as Squyres was concerned.

Don, I don't think I've yet seen you address the question of why the blueberries would be so well distributed within the fine suplhate-rich layers and yet be of such different composition from them if these rocks were laid down by the same surge process. Wouldn't the mixing that occurs within the surge cloud, and the tendency for items of like mass to travel like distances (and of unlike mass to travel unlike distances) tend to sort out the gravels from the fines? An atmosphere would only tend to accentuate such sorting, I would think.

I just don't think we're seeing the kind of sorting one would expect between the heavy hematite-rich ferrous gravel and the sulphate-rich salt fines.

Also, how does the impact surge theory account for the apparent "feeder" formations into blueberries still in place -- small stalks of blueberry-like material leading in random directions from many of the in-place berries? These make sense if you picture the berries as concretions, formed by water flow within microfractures in the salty rocks. I don't have a feel for any inherent process in a surge that would account for them.

-the other Doug

It all comes down to what you really want out of an MSR mission. Remember, Mars is a fairly big planet as far as rocky planets go. It has a significant gravity well which requires a lot more energy to escape than, say, Luna requires. It also has an atmosphere that gets annoyingly in the way as you try and leave, requiring more energy to achieve orbit from the surface than an airless body would.

So, sending a sample off the surface and back into Mars orbit is not an insignificant operation; it takes more fuel than you'd think. If you include the fuel needed to inject the sample into a trans-Earth trajectory, as well as the heat shielding needed to get it back to Earth intact, you're landing an awful lot of mass on Mars that is dedicated to the return-to-Earth systems. (I'm trying to get y'all used to the idea that an MSR return-to-earth stage on a lander is going to need to be a *lot* bigger, beefier and energetic than, say, the upper stage used by the Russian Luna sample return landers. It's not the "model rocket on a Viking" setup some artists have imagined, it's more like landing a Thor or a Delta on Mars and having it ready to launch with no ground support equipment beyond that you bring with you.)

It would take an Ares V to get such a lander onto Mars with the ability to return more than a few grams of soil and rocks. Such a lander would be so heavy with just the fuel and other things needed to get your sample back to Earth that you'd have no mass left for roving to look for and pick up good samples, much less for a comprehensive survey sensor package.

So, even though it requires three separate launches and spacecraft busses, the concept of splitting the mission into three major pieces -- the survey spacecraft, the surface launch spacecraft and the return-to-Earth spacecraft -- lets you distribute the weight required into pieces that don't all have to be landed and don't all have to support Earth return. Remember, the same booster can get kilograms into Mars orbit that can only get grams onto the surface.

So -- if you want a single scoop of Martian soil, a sample that weighs no more than two or three kilograms, then a single spacercaft architecture is usable. If you want to return tens of kilograms of samples, and not just whatever a scoop can pick up from off the side of the lander deck, you're actually better off with the three-spacecraft architecture. Until and unless we make some propulsion system breakthroughs, it's just not energy-economical to do it with the single spacecraft concept -- not to get enough of a sample back to make the mission worthwhile, anyway.

-the other Doug

The Agena was originally developed as an upper stage that would serve as the foundation for the early Keyhole (or KH) spy satellites, but it was used from the outset as a generic upper stage for the Atlas rocket. Not only was it the upper stage of choice for many satellites and planetary probes throughout the early and mid 1960s, it also served as the rendezvous target for Gemini spacecraft.

IIRC, the Agena was the first three-axis-stabilized upper stage developed by the U.S. That made it quite in demand for planetary probes (which, at the time, you didn't want to put into a spin prior to escape trajectory injection), as well as for any satellite that you wanted three-axis-stabilized but didn't want to spend the time and money to develop an RCS for... This was a requirement for the early KH series, but it was a happy circumstance for a whole generation of spacecraft designers.

As for SEASAT in particular, I don't believe it was primarily an NRO type of mission. Yes, a lot of the SAR flown by the U.S. has been NRO-related (primarily to get good ground elevation maps for cruise missile navigation), but SEASAT itself was, IIRC, for scientific research. It's easy to confuse this, since the USSR flew a lot of oceanic radar surveillance spacecraft whose jobs were to track U.S. naval movements (including, it was hoped, shallow submarine assets). The Russian SAR required so much power that they flew with actual fission-pile nuclear reactors; it was one of these that crashed onto Canada, spreading nuclear material over the countryside. American SAR missions have used solar energy (or, in the case of the Shuttle-borne SAR, fuel cell-generated power).

-the other Doug

No -- the mylar thermal blankets on the MESA worktable attached to Apollo 11's Eagle had been signed by the closeout guy, with a note of good wishes. It was on the inside of the thermal blankets, and wouldn't be seen until Armstrong uncovered the MESA for use on the lunar surface.

Neil, the nice guy that he was (and is), said nothing about it on the air-to-ground, and nothing in the official debriefings. He told a couple of people about it on the quiet, IIRC with the admonition that *no* consequences come down on the guy who did it. As I understand it, the guy who did it was given a verbal reprimand by his bosses at Grumman, but otherwise was not punished.

-the other Doug

I think you have the right idea, MII. I know that during the telecon yesterday, SS made several statements about how they were planning a very specific route that addresses rover safety above all. He said that they would *not* deviate from this route in order to go after interesting-looking targets, but that they may stop *along* this route to look at interesting targets of opportunity.

Whatever the rationale, this route has been selected to maximize the safety of the rover and to get it to the bright-band exposure that is the top scientific priority of entering the crater. Any deviation from this pre-selected route will come only from rover safety concerns, methinks...

-the other Doug

My interest in Mars ranges through the entire gamut -- origin, early climate, geological processes, atmospheric evolution -- the whole nine yards. Heck, my interest in all of the bodies of the Solar System ranges through the same gamut (as appropriate -- I don't think atmospheric evolution and early climate issues are very applicable to, say, Mercury).

All of these processes are contributing factors to a very large system. Becuase of its complexity, this system *must* incorporate a large number of chaotic factors, but as in any complex system, order seems to rise from chaos and develop mechanisms which maintain and enhance order. It is this basic creative force (for want of a better term), working against entropy, that fascinates me the most. All of the disciplines we have discussed serve to investigate different aspects of this basic force -- the force that counter-balances entropy and serves to create order from chaos.

In a way, my interest in and exploration of the natural sciences is simply my way of exploring the face of the creative force of the Universe... It comes as close to spirituality for me as anything else, and holds a similar place in my life as religion holds for many people. Which is why I take all of this so seriously...

-the other Doug

Steve was just asked what goals they might have after finishing with Victoria.

He said there are two science investigations they want to execute out on the plains after we finish with Victoria -- the first is the cobbles we've been blowing by as we've been travelling. The ones we've looked at, some are meteorites, some are local bedrock, and some are just weird. They might be from a long ways away, or they might be from deep down and excavated by Victoria. We want to put together a story about rocks we could never drive to.

Second is following up on discoveries we made at Erebus (festoons and such). He's talking about going to similar ancient, eroded craters like Erebus, but not necessarily back to Erebus.

No mention of any kind of Big Crater/Ithaca.

OK -- I have to run, so that's it for summaries from me for now. I hope people have enjoyed them!

-the other Doug

p.s. -- thanks for taking up the task, Doug!

Not a problem, though I'll have to leave to go to work here in about 15 minutes. They're taking press questions now, so we're getting some repetition in information as people ask questions that have already been answered in the presentations.

This last question was a sort of muddled one about whether it would be easier and cheaper to cut down on communications with the rovers and just use auto-nav and auto-drive features of the updated software... Callas is emphasizing that we don't use DTE comm all that much, relay through Odyssey is a lot more energy-efficient.

-the other Doug

Squyres: "The sole basis of our scientific rules of engagement entering the crater is rover safety. The next priority is finding a safe way to approach the bright band. We will not detour from the safest path for a lot of targets of opportunity, but if we see interesting things along the way, we may stop and do some science. But we won't deviate from our path to look at other interesting things." (Paraphrased.)

-the other Doug

More updates -- Steve says that the biggest concern about entering Victoria is the greater danger of failure to the drive mechanisms (wheels, steering actuators, etc.) working on the steep slopes. He reminded us that when Oppy worked in Endurance, she was a much younger rover. He flat-out stated that if we lose a wheel inside the crater, when we *know* we'll just barely be able to get out with six good wheels, we'll never get out.

Alan Stern just commented on funding -- he sort of evaded the question by simply saying that the entry into and exploration of Victoria is, for the time being, covered by the currently approved mission extension. He wouldn't go into what might be decided for later extensions. And John Callas followed that up by saying what I've stated -- as long as the MERs remain mobile, every extension is a brand-new mission and would be sold to NASA HQ as such. Leaving unspoken but very strongly implied that an immobile rover would be harder to sell for an extended mission.

-the other Doug

Specifics on entry -- they'll go to the southern end of the northern lobe of Duck Bay and do their initial toe-dip at that point, followed by entry. There is a ripple that follows the northern lobe, they want to cross it where it appears thinnest, at its southern tip.

-the other Doug

Edit -- toe-dip (which ought to define "entry") looks like it will happen on Saturday, July 7 or Monday, July 9.