Here's a nice space.com write-up of the press conference a lot of the MER science team presented today (Tuesday) at the AGU meeting in New Orleans:

link

I was especially intrigued by Squyres' comments on the stratigraphy seen at Methuselah and Jibsheet, and how it relates to the possible water-fill of the crater at some point:



Sounds a lot like the sequence I laid out in a post a few days ago:

my old post

It is just astounding to me that these plucky litle rovers are able to perform so well as field geologists that we've been able to characterize the history of these sites as well as we have thus far. Having this internet-provided ringside seat to the exploration of Mars (albeit by telepresence) has been exhiliarating. I'm *really* going to miss these rovers when they finally die, you know?

-the other Doug

Yeah, according to the description I read of the maneuver they decided to use, they were going to exit back the way they came, but in a left arc (left in their current direction of travel, which happens to be "forward" since they were driving backward when they got stuck).

It also occurs to me that they don't want to just back straight up, since that puts them heading right back up a dune they had just climbed -- possibly putting the front wheels on that dune before the rear wheels clear the sand trap. A left-arc exit lets them increase the amount of time the three left-side wheels spend on the (presumably) firmer inter-dunal soil. It also, it would appear to me, gets more wheels into the inter-dunal soil more quickly, and for a longer time.

Of course, it *does* sort of look like a right-hand arc would be a better choice to maximize wheels in the inter-dunal soils, but the stuck steering actuator would probably make that pretty difficult, especially pulling out of the trap...

-the other Doug

It is a little more complicated than that.

I hate to disagree with the explanation above, but the way *I* always heard it was this:

The first factor in the ratio is, indeed, distance from an eyechart. The *second* factor is point size of type.

Someone with 20:20 vision can't resolve type smaller than 20-point from 20 feet away. Someone with 20:40 vision can't resolve type smaller than 40-point from 20 feet away. If you have 20:200 vision, you can't resolve type smaller than 200 point from 20 feet away.

There are some people with 20:15 and even 20:12 vision. This is extraordinarily good vision -- it means they can resolve 15-point or even 12-point type from 20 feet away.

As you can see, this allows the ratio to actually measure visual acuity. If it were simply a comparison between better and worse vision, as suggested above, it would have no absolute value and therefore would be a rather meaningless measure.

The "20:20" thing doesn't have anything to do with apparent size of objects, anyway. That's governed by the degree of curvature of the camera lens. I know that in regular photographic equipment, objects appear in fairly normal perspective (i.e., as large and small, by distance, as they would to a human eye) when you use a 50-mm lens. A wide-angle or "fisheye" lens, of 35-mm or less, makes objects appear farther away than they are (smaller at a greater rate with distance than we see with the eye). A narrow-angle, 75-mm up to 500-mm or more, makes distant objects appear much closer than they are (smaller with distance at a lesser rate than seen by the eye).

-the other Doug

As I understand it, the original television signals were not captured and recorded, the only permanent record of the images are these negatives and any prints made from them, correct?

Let's see -- the Surveyor camera had a low-res 200-line mode and a high-res 600-line mode, if memory serves. It seems to me that what *really* needs to be done is for the negatives (yes, all 80,000+ of them) to be scanned directly, using a scanner that scans each individual line of the television image and generates a "line" of pixels that most closely represents that line of the original television signal.

You could then assemble those lines into digital images that can be both stored far longer and more securely than the negatives and can be manipulated to create highest-possible-quality images and panoramas. (Since you're scanning negatives, you'd just reverse the grayscale somewhere in the process to create positive images.)

In addition, since the mirror position on the camera was probably slightly variable, you might even be able to generate super-resolution images by overlaying images taken of the same scene in the same lighting conditions. At least three of the Surveyors survived long enough to image the same patches of real estate several times at very similar lighting angles over two or three lunar days.

It would not be a cheap process -- it would have to be a government-funded project, I imagine. Maybe it could be sold on the basis of preservation of historical data. But I can well imagine being able to design a scanning system that would accurately scan each TV line and create a high-quality digital version of the image. It would require precise negative positioning control and the width and "targeting" of the scanning beam would have to be custom-designed and precisely controlled, but given ten or fifteen million dollars, a staff of 10 or 15 people, and a couple of years, I bet it could be done quite effectively.

-the other Doug

Oh, I wasn't saying they didn't do some amazing things with that instrument. My point was (and remains) that it was not primarily an imaging system, and because of that, it was unable to take anything like the total number of pictures a dedicated imaging system would have, and, indeed, the highest resolution Pioneer images I've ever seen, though they may have similar theoretical resolution to Voyager images, all appeared to retain aberrations and "blurring" factors that made them appear far less clear than the average Voyager image.

I suppose it's possible that I have never seen properly corrected and cleaned-up Pioneer images -- do you have any links for high-quality versions? (Beg, beg...)

-the other Doug

I have never seen a man more completely enraptured than Walter Cronkite after his experience of holding the glass wall up to keep the acoustic pressure of the Saturn V from pushing it into his booth. I think his reaction to the physical *presence* of the mighty Saturn was even more profound than his speechlessness a couple of years later when men finally landed on the Moon.

-the other Doug

Tommy Gold's problem wasn't that he thought outside of the box (which claim I question just a bit) -- it was that, in the face of overwhelming evidence that his theory was invalid, he not only stuck to it, he got louder and more shrill about it right up to the point where men actually walked on the Moon.

Face it -- after two successful Luna and five successful Surveyor landings proved that the lunar regolith was sturdy enough to support all sorts of weight, the man was still strongly (and publicly) pressuring NASA to include a set of large weights with brightly colored flags attached that were to be shot out in front of the LM as it descended, to make *absolutely sure* that the surrface below wasn't a meters-deep quagmire of lunar quicksand.

"Thinking outside the box" is no excuse for vociferously hanging on to theories that have been discredited.

-the other Doug

"Duricrust" is a term that was applied to some Viking soils back in the 1970s, to describe the cohesive properties of the upper few mm of some of the soils. As far as I've ever been able to tell, it's used in a descriptive, not a diagnostic, manner -- it describes the cohesive qualities of some top layers of Martian soils. It doesn't pre-suppose a reason for the cohesiveness, i.e., it doesn't assume that the duricrust is created by a permafrost layer or anything like that. (So the idea of an absolute "true duricrust" doesn't really enter the discussion, I don't think.)

In fact, the conclusion of the original Viking team was that the duricrust is likely a weakly cemented unit resulting from evaporation of salts from groundwater. Since no evidence of current groundwater was returned, they didn't state that assumption as certain, but I know it was the preferred theory for the observed phenomenon.

-the other Doug

I think you mean "undesired velocity." Expectations, after all, vary with the person doing the expecting. And from what I've read, even several Soviet engineers had less than full confidence in their early Mars landers' abilities to land safely...

-the other Doug

Sorry, I took Sol 479 two days ago...

-the other Doug

I think he wants patio furniture that has six wheels and an uplink capability...

-the other Doug

The background and general area look quite lifeless and wild to me -- but in the foreground of the first four images, there is *definitely* a trilobite fossil! It's as obvious as anything! And if any of y'all can't see it, that just proves my own very special and God-like powers of observation and analysis!



-the other Doug

I'll say Sol 479, but that we won't drive very far (less than 20 meters) from the "free" spot for another three to five sols after that.

-the other Doug

I see what you mean about the dip vs. the strike. Well, I have a hard time positioning myself when looking at the surface images, in re direction.

So, the hills may have been uplifted from bedrock that already had a dip, eh? Curiouser and curiouser...

-the other Doug

We've all seen the dust devil movies posted May 6 at the JPL MER site... but I haven't noticed anyone mentioning the last set on the page. Not only does that last movie capture the by-now "standard run" of small dust devils dancing across the plains, it captures two of the very large variety, whose bases were likely hidden by the curvature of the horizon but which you could see towering into the air hundreds and hundreds of meters.

These are the *big* dust devils that have been observed from orbit. I was beginning to wonder if they co-existed within Gusev with the smaller variety. I guess I never made it to the bottom of that page before today... shame on me.

Here's the link -- notice that while there is one very obvious large devil on the horizon, there is another one about one-eighth or of the image width to the left of the strongly visible devil that blows in and out of view:

JPL MER Site

The large devils on the horizon look quite a bit different from the little ones we can see dancing along the plains in the foreground -- they're taller, they entrain more dust, they remain coherent for longer periods, and they move more slowly (at least relative to the frame). During the time the major large devil takes to move a tiny amount, four or five little devils dance across the frame out on the plains. In fact, it looks like one little devil passes very, very close to Spirit, near the end of the sequence.

-the other Doug

These newly-available analyses suggest to me a slightly modified sequence of events at Gusev:

1 - Creation of the ancient crust, actual minerology still not definitely determined.

2 - Creation by large impact of Gusev crater.

3 - Covering of the floor of Gusev (at least in some areas) by pyroclastic materials, something like ashflow tuff. Possibly over several episodes.

4 - Uplift of the Columbia Hills and other landforms, both within Gusev and extending on a fault line to the north of Gusev, exposing the layered beds of pyroclastic deposits along the fault line.

5 - Inundation of Gusev by very salty and probably acidic water, altering the ashflow tuff-like materials in the hills up to the level of standing water. This water inundation would have eroded and altered the olivine in the lower hills, breaking it into constituent elements and creating the hematite and other water-alteration byproducts we see in the West Spur rocks, but leaving the rocks farther up the hill relatively unaltered.

6 - Evaporation of standing water inside, and slow loss of some of the groundwater beneath, the Gusev floor.

7 - Flooding of the crater floor by basaltic lavas which embayed the uplifted hills, but to a lower level than the water had embayed those same hills.

8 - Migration of remaining groundwater up through the basalt "cap" flows, creating minor but detectable alteration of the basalt beds.

9 - Then, for the most recent several million/billion years, the whole thing gets slowly sandblasted by an ever-thinning atmosphere, creating ventifacts and other aeolian weathering features.

And there you have it -- a recipe for the creation of Gusev Crater as it exists today.

-the other Doug

Stratigraphically, what we really want is to get *lower* in the sequence, not higher. The lower we get, the older the rocks. And the older the rocks, the more complete the story we can buld up as to the history of geologic, aqueous and atmospheric processes that carved this landscape.

With the discovery that the Columbia Hills seem to be formed out of dipping beds of layered rock (which had to have been uplifted by tectonic or impact activity), it makes sense that the summit of the hill would become a lower priority. Getting to the summit just means we're following along the top of the stratigraphic sequence. Think of taking a piece of plywood and breaking it, then propping it up so that the broken edge sits at an angle above the tabletop. If you just move along the top of the piece of plywood to the point highest above the table, you're not going to gain any deeper insight into the structure or composition of the plywood -- you'll be staying right on top of the top layer. And in the hills, the "broken" edge of the layered bedrock has been spilled down and eroded such that it's mostly a jumbled mess.

It sounds like they've identified a spot where a much lower section of the stratigraphic sequence is exposed in place. To a geology enthusiast, that is a *lot* more exciting than getting an impressive view of what are, after all, drab ochre plains stretching into the distance....

-the other Doug

The following comes from my recollection of the supporting text in the NASA publication "Exploring Space with a Camera," where the landing point and orientation of the lander were discussed in detail.

The "mountain range" visible at the horizon in Phil's first image *may* be the northeast rim of Tycho. It may also be the ejecta ridges concentric to the rim.

Surveyor VII landed about 40 km northeast of the main rim. The topography is *still* poorly-enough understood that it's not clear whether or not the ridges of ejecta would break its line-of-sight to the uplifted rim. But the mountains visible on the horizon are in the right direction to be the actual rim -- if the rim sticks up high enough to be visible from 40 km away.

-the other Doug

Phil, is there anywhere you can post the full-resolution images (even temporarily) where we can link to them? I would *really* like to see them at full resolution... *smile*...

-the other Doug

The problem was more that the imagery was crude and nearly an afterthought -- it was crude by the standards of the time in which it was built.

The Pioneers were limited in that they were primarily fields-and-particles sensors. The magnetometers, especially, worked a lot better on a spinning spacecraft. And it's really tricky to develop a stationary, pointable scan platform on a spinning spacecraft. The Voyagers managed it, but they're bigger, better spacecraft than the earlier Pioneers.

So, since it was just cost- and weight-prohibitive to equip Pioneer with a stationary scan platform, the best they could do to provide imagery was to place a photometer on it and have the Pioneer's own spin scan the photometer through its field of view, one line per rev. The photometer was "nodded" on each scan to get an adjacent line.

That kind of imaging is rather inherently crude and low-resolution. It needed an awful lot of correction, because of precession of the spacecraft spin and the distance the spacecraft traveled relative to its target during the time it took to build up a single image.

But it was a HECK of a lot better than nothing!

-the other Doug

Your work should be hanging in a gallery somewhere, Nirgal!

I truly think you have captured Mars, here. At least the Gusev slice of it. Now I feel like I truly know what it would look like if I could stand in those hills and look out over the plains.

-the other Doug

I'd be glad to help out... just let me know what you want me to do. (I may only be a technical writer by trade, but that *does* make me a professional writer...)

-the other Doug

Thanks, guys -- I didn't mean to come off as Board Monitor or anything. I just wanted to see some discussion about the nature of Jibsheet, since it's a rather unusual-looking rock that would seem to be shedding clasts or inclusions onto the ground. I guess I'm a little surprised that none of our other amateur and professional geologists have any opinions about it...

-the other Doug

The difficulties in getting the Apollo deep cores out of the ground had nothing to do with temperature. On Apollo 15, the extreme difficulty (both in drilling down and pulling the core back out) had to do with a design problem with the drill stems and the extraction equipment, as well as the tendency for lunar soil to become highly compacted just a few millimeters below the surface.

I don't think there is a really "hard" surface under Oppy's wheels as they're stuck in the drift. I just think that's as deep as the wheels go in with this consistency of powder, the wheel design, the weight of the rover, etc.

Remember, there's nothing in the way of liquid water left in this dust, so "freezing" it shouldn't have any gross effects. And the temps during the day on Mars are also generally below freezing, so the temps are overall too cold for us to see any "change of state" difference -- based on water, anyway. And none of the other atmospheric components or soil components would change state readily over the temperature ranges at Meridiani.

-the other Doug

Ummm... correct me if I'm wrong, but doesn't this PNG vs. JPG discussion belong in the Imagery Issues forum? I glance through that forum, but as someone who's more interested in the geology and meteorology on Mars than in the technical details of how to play with the pictures, I guess I'd like to be able to glance through the imagery issue discussions separately....

-the other Doug