We're all mixing apples and oranges a bit, here. We're confusing the rule which causes orbital clouds of particles to fall into planar rings, and the full range of tidal effects on solid bodies.

AIUI, clouds of particles work into planar rings because they eventually all impact each other as they cross through the equatorial plane. The net effect of all of these impacts is to reduce the out-of-plane vectors and neatly sort the particles into thin equatorial rings.

The effect of tides on larger bodies is mostly to lock the small bodies into a primary-facing orientation. Tidal effects have locked Iapetus into having one side that always faces Saturn, and yet those same tidal effects have not changed its orbital inclination to one closer to the rest of Saturn's moons. Perhaps tidal effects can make closer-in moons orbit in a more planar fashion, but with outer moons they seem to have far less effect.

I believe that the tendency to flatten a cloud of debris into the same plane is dependent on the density of the cloud. As you move out from the Sun, the planets are all in the same general plane (the ecliptic), but bodies formed in the much thinner outer regions of the original solar nebula, where planar collisions were much rarer, diverge greatly from the ecliptic.

Just the same, gas giant satellites that formed in the outer portion of their planetary nebulae would undergo fewer planar collisions and you'll see greater and greater divergence from the planetary nebula plane with distance. And for satellites, you not only have effects from bodies in the planetary nebula, you also have influences from nearby planets (especially big ones like Jupiter and Saturn).

I think it's very likely that all of the major bodies in the solar system originally had very little divergence from the ecliptic, having all formed out of a planar solar nebula. But the final stages of the accretion process generated all sorts of odd momentum transfers. One planet nearly stopped turning on its axis entirely (Venus), one was knocked onto its side (Uranus), and several other planetary axes were knocked from five to 30 degrees off of the ecliptic.

We need to think of the current state of the Solar System and its objects as the pretty-much-final configuration resulting from the chaotic final phase of accretion. The system remains dynamic, but accretion has been finished for all practical purposes for more than four billion years. Solar System bodies have had the same ranges of inclination, the same divergences from planar, etc., for many billions of years, and unless a new set of bodies invades the system, it's liable to stay relatively stable for several billion more.

-the other Doug

I just want to point something out about the whole Pluto furor. For those of us who question why it matters whether or not Pluto is a planet or some other thing. It's a bit of a sideways look at it, but it says something important.

Here in Minneapolis, there is a comedy troupe called the Brave New Workshop. Their latest production is entitled "Pluto, and Other Lies My Teachers Told Me."

Sort of puts the whole mess into a new perspective, doesn't it?

-the other Doug

Doesn't surprise me a bit, Mike. I know exactly why, too.



-the other Doug

Rotation between the two objects in a contact or near-contact binary may occur around a mathematical "center of mass" of the two bodies. But I'm thinking that only actual *mass* can generate a gravitational field. The spot where their gravitational fields interact and counter-balance may define their common center of gravity, but it would not in and of itself exert any gravitational force. The most it could do would be to collect a smallish amount of dust in its own little Lagrangian point(s).

So, the greatest gravitic attraction to a mass on the surface of such an asteroid would be the vector towards the largest and closest attracting mass. Since a process of pulling material off of each body would be a dynamic process, I'd guess that whenever you got to a point where the other body exerted more pull than the body on which a given item (rock, dust particle or even astronaut) is sitting, all of the loose stuff would settle into new, stable configurations. Thus the rock pile masses that seem to connect several large pieces of Itokawa.

We're talking really small masses, here, when it comes to actual gravity field effects. We don't know exactly how much force holds the various pieces of Itokawa together, for example. The whole thing is only the size of a smallish hill. Could an astronaut, using just his/her muscles, actually shift one of the large pieces of Itokawa such that all of the stable configurations become newly dynamic? Or would it take a lot more energy than that to accomplish any serious movement of the big pieces against each other?

All I know for certain is that, until we get out and actually start doing it, we won't know just how non-intuitive all of this might end up being. But I bet it'll take a lot of getting used to...

-the other Doug

But, guys, note that it's not just the general public who are in the dark about the data being collected by VEx. Please note the opening in another thread from someone actually working VEx Mission Science Operations:

Here is someone who seems to have responsibilities in the planning of continued science operations, and yet he is waiting for an issue of Nature to come out to see what results the individual PIs are seeing!

Correct me if I'm mistaken, but it appears that science operations planning is being done without the benefit of much in the way of data getting leaked back to the planners by the PIs.

Seems to me this is a system that grants the PIs *far* too much power and secrecy. They are guaranteed a lion's share of the credit for any discoveries made by their experiments, they ought not be so paranoid about anyone other than themselves seeing anything beyond what The Wizard decides to allow us to see in His published works... *sigh*...

-the other Doug

Emily, whenever you are being driven insane, just do what I do -- thank your Maker it's such a short drive!



-the other Doug

I just noticed that it seemed like a while, again, since we've heard from Bob Shaw. Checked his member info, and he hasn't been logged on since January 26th.

Anyone know if he's having connection problems again?

-the other Doug

Looking at the features along this portion of the rim a little more carefully, I get a gestalt impression of the entire landmass that contains the current capes and bays having slumped down fractures as the pressure of the mass in the rockbed has decreased as the rockbed has descended into the crater pit.

Look at it this way -- the Guam area, and the area along this new linear feature, are all places where the land between the feature and the rim of Victoria has slumped down a bit, a few centimeters here and there. No more than half a meter, I'd bet, anywhere along the line. Now, these may have been impact-created fractures or they may have been pre-existing, but as mass was removed from the rockbeds between these fractures and the rim of the crater, the entire rockbled has slumped along these fracture lines. Leaving these little ridges that we're seeing, here.

Looking at it, my first impression is that the Guam formation represents slumping along an impact-generated fracture, while this linear feature is along a pre-existing linear fracture within the rockbeds.

-the other Doug

It's a little tough to say whether the feature in question is linear or arcuate, though I admit it looks more linear to me. (If it's arcuate, it's not really concentric to the impact point, is it...?)

-the other Doug

There is really only one example of a Cassini discovery that was self-obvious in the compressed JPGs -- the Enceladan plumes. And y'all will recall that as soon as one of us spotted the plumes in the JPGs, we were immediately told by a member of the imaging team (who posts here) that all we were seeing were lens flare effects. And he didn't retract that opinion until after the imaging team went public with their own conclusion that there really were plumes coming off of Enceladus.

I'm not saying anything except that this coincidence caught my attention at the time, and I still note it in this discussion...

-the other Doug

So, we're seeing any number of faults in Victoria's walls. Here's the question -- how much of this faulting was caused by the impact event, and how much was already there when the impact occurred?

I think that the faulting that causes features like Guam (aka The Dock) was caused by the impact. Impacts can cause arcuate faulting in the surrounding rockbeds that is roughly concentric to the crater rim. These arcuate faults tend to form in lobes, rather than in perfectly concentric circles, probably controlled by pre-existing faulting and also by changes in the tensile strength of the rockbeds through which the seismic shock passes. (I'm very tempted to say that Guam defines where a cape and bay will eventually appear as Victoria continues to erode, and I'm also tempted to say that such impact-related faulting has created the cape-and-bay structure we see now.)

I'm also tempted to say that a majority of the faulting we're seeing in the walls themselves is also impact-related, being the result of the extensive fracturing that the rockbeds underwent during the impact process. But it's very possible that some of the faulting was controlled by existing faulting in the rockbeds. (Note that this means there is something about the rockbed target of the Victoria impact that created these cape-and-bay fault structures which doesn't occur around most Martian craters, since most martian craters don't exhibit the same cape-and-bay rim structures.)

The straight-line faulting we see in the east-southeast wall looks more like pre-existing faulting that is now controlling how Victoria's rim is eroding along that edge of the crater. I doubt that this particular straight-line fault was exposed by the original impact -- it's only becoming visible as the crater walls erode and slump back to it.

I think that a computer-generated model of the cracking patterns one could expect in the types of rockbeds we've observed at Meridiani from a Victoria-sized impact could shed some light on the various fracture planes and fault lines we're seeing in the walls, here...

-the other Doug

This is the old argument they went through when they were designing the Apollo system. They asked themselves, how much would it cost to develop a system that would have a 100% reliability rating, that could never fail and never, ever endanger the lives of any of the crews.

They decided it would cost more than the entire American gross national product from then to their deadline (the "end of the decade") to accomplish that, and it would likely result in a first manned lunar landing sometime around 1980.

They also figured they could develop Apollo for about five billion dollars if they were willing to lose about half of the crews they launched.

They settled on having a 90% chance of completing any given mission, and a 99% chance of getting any given crew back alive. That determination *alone* set the cost of the program at about $25 billion in 1960s dollars.

So, yes, you can pursue perfection. Just understand that, first, you'll never achieve it, and second, that you'll spend an *awful* lot of time and money trying to get there.

The better is the mortal enemy of the good enough...

-the other Doug

I will simply address the "safe" question here -- is it worthwhile to do more work on the Moon?

I think the answer is unequivocally YES. Our Moon has a surface area roughly the same extent as the continent of Africa, and we have looked really craefully (with manned landings) at only six locations, and a little less carefully (with unmanned landers) at ten others. We've done some medium-resolution mineral mapping of the rest of the surface, but we don't really know how the mineral signatures we see from orbit relate to the actual evolution of the rocks on and under the surface.

Libration data suggests that the Moon not only has a core, but that its core may rotate at a slightly different speed than the rest of the body! But detailed analysis of volatiles and trace elements deposited on the surfaces of glass beads erupted in lunar fire fountains indicates garnet in the mantle and core rocks, which argues against a large bulk of the Moon having ever been molten (i.e., it is still made up of chondritic material).

And, since our best models don't allow for all of these things to have developed in the same body, we have very little clue as to how all of this could happen.

Developing models that explain *all* of the observed facts will require more data from the Moon. And yes, it will require more data from the Moon's surface. We can argue endlessly as to whether we ought to pick up more Moon rocks with gloved hands or with robotic scoops, but I don't think it's possible to successfully argue that there is no need to even *try* to pick up any more.

-the other Doug

Dealing with death is one of the hardest things we have to do in life, Stu. And when it comes to putting down a pet, no matter how "right" the decision is, you never get to make it without it tearing you up a little.

But the sadness will pass, and soon all you will really have left are the happy memories and the ineffable presence of Amber's spirit, which will be with you always.

Until then, our hearts and prayers are with you.

-the other Doug

I'm not positive about that sinkhole theory, nprev -- looks to me like many (if not most) of the lakes occur within the walls of circular depressions, but it also looks like they fail to fill the entire depression in most cases. Looks more like they might have entirely filled the depressions at some point, but have evaporated down to remnants at this point.

The depressions look more like old impact craters than calderas to me, but that's a hard distinction to make with the resolution that we have.

-the other Doug

Thin-slice? How about electron microscopy? Seems to me that they had to resort to such high magnifications to see what appear to be microfossils in that Martian meteorite. If all the little critters on Mars grew that small (not an unreasonable conjecture, given the harsh conditions and lower average energy levels in the environment), we'll need a rover that can prepare samples for, and subject them to, electron microscopy.

Sounds like a real challenge. Especially considering that there were plans (a long time ago) to provide Apollo astronauts *on the lunar surface* with equipment to make thin rock slices (part of the two-week lunar stay, dual-launch proposals for extended Apollo landings). So, I think that there are lots harder things to do, even remotely, than making and observing thin slices...

-the other Doug

I sort of forget what it was first called, but the program in question was called Apollo Extension Systems (AES) for a while, before being renamed Apollo Applications Projects (AAP).

The whole idea was to come up with ways to use the Apollo technology for missions other than the basic lunar landing mission. These not only included expanded lunar expeditions, they also included a rather wide variety of space station, space astronomy and other missions. Heck, there were even plans for a "fast" manned flyby of Venus using Apollo technology.

It started out with the concept, "Here we have these great spacecraft. What else can we do with them?" When most of the suggestions began to involve designing and building large, complex new spacecraft to fly with Apollo CSMs (after all, the space station concepts required you to build the space stations), the question was modified to "What else can we do with them with minimal additional design and development?" This was when the name changed from AES (which encouraged extending the Apollo systems) to AAP (which simply encouraged the use of existing Apollo technology, with as little new spacecraft development as necessary).

As always, these changes reflected dropping Congressional support and funding levels.

As time went on and those AAP programs which *could* be funded were identified and given green lights, they fell out of the AAP umbrella and either became their own programs (SkyLab, ASTP) or were incorporated into what was called "mainline Apollo" (as the final three expanded lunar expeditions). The rest of the grand plans that never came to be are now delegated to the great dustbin labeled Great Missions That Never Were...

-the other Doug

Sounds a bit like this Car Talk program on the radio here in the U.S. IIRC, the hosts call themselves Click and Clack, or something along those lines, and they offer a lot of interesting programming. Including, once, a "phone call" from a crewman on a Shuttle flight that was then on orbit!

That was a really cool call -- the astronaut (I know his name, just can't remember it right now) started out saying he was having some problems with this government-issue truck. It was "one of those Rockwell trucks," he said. It started out running real loud and real rough, and you'd swear it was going to shake itself apart, but after about two and a half minutes, it smoothed out a lot and got a lot quieter. Problem was, it always seemed to run out of gas after running only six and a half minutes or so. That was OK, he said -- he could usually then just coast to wherever he was going.

One of the hosts figured it out pretty quickly, and his first question was to ask where the guy was calling from. Still being cagey, the astronaut said "About two hundred miles away from Hawaii." The host said "Above Hawaii?" and the astronaut, bursting into laughter, managed to say "Yep!"

It was a classy experience...

-the other Doug

That's one interpretation. Another interpretation of the craters with bright rims and dark floors is that the entire crater was once all dark, but mass wasting has exposed brighter materials in the rims.

I tend to agree, though, that the dark stuff probably was emplaced over top of the craters, and happened pretty much after all of the visible craters were formed.

-the other Doug

Yep, the example you showed from the Encyclopedia Astronautica was one of the really large man-tended telescope concepts that was considered in the mid-60s. Interestingly, the Apollo Telescope Mount went from a few solar telescopes attached to the Service Module to a concept of using a Lunar Module as the basis of the ATM. The original LM-based ATM designs showed a basically unchanged LM ascent stage, which would have served as the control room for the telescopes, while the descent stage was replaced by a suite of solar telescopes housed inside a LM descent stage's octagonal frame.

The final version of the ATM flown on SkyLab was actually a rather severely modified version of the LM-based design. If you look closely, you can see that the main structure of the flown ATM was the same size and octagonal shape as a LM descent stage.

-the other Doug

I also remember Pioneer 11's Saturn flyby quite well, and I have to admit that my reaction was more one of disappointment. I had really looked forward to seeing the first images of Saturn's rings "in all their glory" from a space probe, and when I saw them, they were poor-resolution, dim, shadow-side images that made me feel I had seen better versions of Saturn from Earth-based telescopic observations.

I didn't see what I *really* wanted to see until the Voyagers arrived several years later. Voyager is still the great wave of enlightenment of the outer solar system, for me.

-the other Doug

Yes, but this is rather like Occam's Razor. There is no need to bring in extraordinary events here; the areas in Victoria where we see these linear features were originally outside of its rim. The crater has expanded via wall slump so that the walls have expanded *into* linear fault features, which more than likely pre-existed the crater. (In fact, I'd say they'd almost have to -- how many craters have you seen that have created faults tangential to their rims? Impacts more commonly create radial cracking than cracking transverse to the impact surge.)

I'm not saying that these fault features are definitely *not* associated with fluid flows. All I'm saying is that linear faults are fairly common on all of the rocky bodies we've observed (Earth, Moon, Mars and Venus) and in most cases these faults are tectonic in nature. Of the remaining sources of linear faulting that have been observed, only a relatively few are related to fluid flow.

So, if it turns out that Oppy can visit these ridges and they turn out not to show signs of fluid flow formation, that doesn't mean there aren't other locations on Mars where fluid flow faulting has occurred. And, conversely, if fluid flow *is* indicated in Victoria's linear faults, that doesn't mean that every similar set of faults we see on Mars were also formed in the same manner. Linear faults are just too common and have too many different causes for such generalizations to always be valid.

-the other Doug

Well, heck, we've been discussing those linear features in the east-southeast portion of Victoria's rim ever since the first HiRISE pictures came in.

While it might be interesting to discover some basic faulting that's associated with subsurface water flow, I think there are so many ways in which the local crust could have been gifted with linear faults that assuming the water flow origin is rather premature.

-the other Doug

Sounds like a good side effect, but I'd bet this is just another attempt to give Visidom something to look at.

-the other Doug

I know what you mean, Doug. When I went to see the IMAX film "Roving Mars," the theater had a full-scale MER model in the lobby. And it was nowhere near as accurate as this one is. Nowhere near at all. (For one thing, the MER model I saw had rubber tires that looked like they had come off of a riding lawnmower or something...)

The interesting thing was, though, that when I walked up to this model (which, for all its faults, was at least very close to the proper size), I found that I was staring directly into the "eyes" of the Pancam. The Pancam lens simulants were at exactly my own eye level.

-the other Doug