Apollo 14's EVA troubles were as much a problem in process as they were a result of the hummocky surface.

There was ample observation from the first two landings that landmarks appeared much closer on the lunar surface than they actually were. This is due to the lack of any atmospheric haze and the lack of familiar objects with which to compare distant objects.

However, they didn't develop a traverse plan in which this difficulty was taken into account and walking speed estimated fairly precisely such that traverse time would give a decent estimate of distance covered. Instead, they designed the distance traveled estimates against passing of specific landmarks and sighting of other nearby landmarks -- a process which was a lot more prone to interference by hummocky terrain and difficulty in perceiving distance.

Because the landmark process was chosen, the Apollo 14 crew spent more time trying to figure out exactly where they were at all times than they spent actually moving towards their goal.

This is the kind of lesson that is valuable to be learned in *any* planetary exploration program -- you have to constantly re-validate your operational processes against your lessons learned. Failure to do so causes problems.

And, BTW -- yeah, I absolutely loved Wilhelms' book, too. My copy has been read over so much, it's in tatters... I also recommend Paul Spudis' "The Once and Future Moon." It does a very, very good job of explaining the petrology and geochemistry of the Moon.

-the other Doug

If I had to guess, I'd say they're looking at Oppy's tracks more than the wheel. I'm seeing a lot of bright compressed soil in the tracks, just like we saw at Gusev where the soil had very high salt content.

I think we're seeing the dust and sand from the eroded evaporite mixed in with these soils, which is causing the spotty bright compressed soil in Oppy's tracks. I think maybe they're taking a close look at the tracks to see if that's what is, in fact, happening. Wouldn't surprise me to see a two or three day session of Mossbauer and APXS integrations on the soils around here sometime soon. Maybe even a trench.

-the other Doug

That's the thread I was talking about. Seems to me the cruise stage had to have broken up into a few pieces, and the mass/drag ratio on a bolt would probably be more weighted towards mass than that of a bigger chunk of the CS, with more exposed surface area. So it might make sense that the dark splotch is the crater from a large, "junkier" piece of the CS and this little tiny dimple is from a much smaller piece that shot out a little further.

It's possible that this is a tiny secondary from the larger CS impact, but to tell the truth, this looks like a primary -- most especially because the impact was likely at a pretty sharp angle and the crater remains circular. At slower speeds, as you see in secondaries from small craters, craters made by low-angle impactors become elliptical. But beyond a certain speed, even low-angle impactors make perfectly circular craters.

-the other Doug

Looks really fresh, though, doesn't it?

I think what we're seeing is the intersection of two surface-altering processes. The first is impact -- since Mars has a very thin atmosphere, the lower size limit of impactors that reach the surface is a lot smaller than here on Earth. But it's a lot larger than what would reach the lunar surface, for example. So, you get more craters from 6 cm on up than you do on Earth, but a lot less than you see on the Moon.

The second process is aeolian weathering. Over the course of just a few years, decades at most, this small little dimple crater will probably be covered over by sand and dust. Which means it's probably quite fresh -- a few years at most. Unlike on the Moon, where the most numerous craters are the zap pits made by grains of dust measured in microns, and where there are no other weathering processes happening, Mars doesn't retain craters of this size all that long. Because of aeolian weathering.

So, the impact flux of such particles must be pretty slow, or else we would see a bunch of these little dimples all over Meridiani in varying stages of obliteration. And we don't. In simple terms, aeolian erosion is happening a lot faster than tiny impacts are happening -- but both appear to be happening.

Seeing as this looks to be a very, very recent cratering event, let's bring up the topic of another thread, shall we? Perhaps this dimple was caused by a stray bolt, or fleck of metal, that separated from Oppy's cruise stage when it broke up and impacted at about a thousand KPH? I mean, going back to the Venn diagrams we did in grade school , there *is* an intersection of the sets "tiny craters made by very small impactors within the last few years" and "space debris that might have broken into some very small fragments that we *know* impacted close to here within the last few years."

I'm not saying this tiny dimple was caused by a tiny piece of Oppy's cruise stage -- but the timing and the size could well be correct. And it seems a bit coincidental that a really, really fresh crater should show up within what must be only several km of the debris footprint of Oppy's cruise stage...

-the other Doug

That sort of pins down the landing site, doesn't it?

Now, where exactly on Mars *is* Grover's Mill, anyway...?



-the other Doug

Well, you certainly have a gift for it, Nirgal. We all realize that there is some artistic license in what you're doing, but I for one don't mind a bit.

If you really want to play with trying to make it look *exactly* like it would look to a human being standing on the surface of Mars, there is a nice discussion of the color hues of the Martian surface in the NASA publication on the Viking landers. I don't have the book anymore, but it was one of their SP- series. One section late in the book shows the same scenes with three different color corrections -- one as if seen in white light, one as if seen on the surface of the Earth (with the blue fill you get from the terrestrial sky), and one as if seen by a human being standing on Mars, with the low light levels and the orangish light fill from the Martian sky.

What you're doing right now looks a lot like a cross halfway between the first two -- white light and Earth lighting conditions. But don't get me wrong -- I really enjoy your vision!

-the other Doug

I think I can say with a fair degree of certainty that insects did *not* cause this pit.

-the other Doug

Well, it's either a small meteor crater (not unlikely, considering the thin Martian atmosphere, that an impactor the size of a grain of sand would hit and make a tiny crater) or it's a small sinkhole.

It's not at all difficult to imagine voids and gaps in the evaporite layer -- after all, subsidence around organized voids probably formed Anatolia and the other cracks we see out in the plains. But this crater, situated halfway up the crest of a dune, looks a lot more like a tiny impact crater.

As such, it would only display the constituents of the sand in the dune... and therefore wouldn't be all that interesting to Oppy's remote sensors. Right?

-the other Doug

As I noted within the last week, here, it looks from the orbital images like there are two different types of terrain between here an Victoria -- the true etched terrain (which features outcrops of evaporite) and a stretch of duned ground that appears to incorporate both dark and light sand/dust in the regolith and duning, but no evaporite outcrops. It's that second type of terrain, which only includes lighter sand in the regolith, that we're crossing now -- in fact, we don't really get to any of the "true" etched terrain until after we pass Erebus (unless we want to make a detour to the west of Erebus, which doesn't appear likely).

I think we're seeing the first examples of eroded evaporite dust mixed in with the broken-up concretion materials that make up the dark regolith out on the dark plains. And if that's the case, since the evaporites are primarily salt-cake rock, it would make sense for the lighter sand to compress into a shinier surface under the wheels -- just like salt-rich soil has been doing at Gusev.

So far, my theory looks pretty good... *grin*...

-the other Doug

Very good point, Bill. Especially about earlier spacecraft. NASA had all of the American craft designed to land on Mars sterilized, I know (the Vikings, Pathfinder and the MERs, as well as MPL), but what about MCO? And IIRC, the Russians did *not* go through a sterilization process on their Mars landers -- several of which sem to have reached the surface, if not in operational condition.

It's very true that a trace of biomatter on a crashed Mars probe is far less likely to contaminate the whole planet than a whole human outpost -- people exist in a veritable soup of microbes, parasites and symbionts. Our very breath contains organic material. Filters designed to keep such particles from moving one way or another are expensive and clog up easily -- they could be an answer for very short-term human stays on the surface, but would become a maintenance nightmare on a months-long stay.

By the same token, it's fair to say that human-delivered micro-organisms would get sterilized pretty quickly by the Martian surface conditions, as would any Martian microbes -- we're going to have to look beneath the surface to find any evidence of the latter, I'm sure.

It all comes down to intentions, I think. If we never intend to try and establish a human presence on Mars, then it makes sense to *never* even attempt to land there -- it would pose far too great a risk of contamination. However, if we *do* intend to put humans on Mars to stay, then by definition we will be *intending* to place a terrestrial environment on Mars (no matter what extent). In which case, the problem becomes maintaining "pockets" of uncontaminated Martian environments for study.

Since we're operating with a severe lack of information on the quantity, distribution and current status of Martian biotics, *any* discussion of cross-contamination -- either way -- is an exercise in energetic arm-waving. And since we're a long way from making firm plans about landing humans on Mars, we have many, many opportunities to expand our data on Martian biotics before we commit men and materiel to *any* such plan. Hopefully, by the time we *do* start serious work towards a manned Mars landing, we'll have more information and can make rational decisions about the contamination risks.

-the other Doug

Great work, Tman! Boy, it really shows how you can't easily tell a crater's age (or at least, state of erosion) from orbit. Vostok, Viking, Voyager and Eagle all look a lot alike from above, don't they? But they seem of vastly different ages from the ground.

I'd guess, from the looks of the ejecta blankets and such, that they are, in order of age from youngest to oldest, Viking, Fram, Voyager, Eagle, Vostok.

-the other Doug

I'm 49, so I was 15 at the time. I remember it *quite* well...

Shepard and Mitchell had stopped *way* short of the planned interim sampling stops, thinking they had gone farther than they actually had. As they climbed Cone Ridge, they came up to a ridge crest that was about 20 meters below the very top of the ridge. As the came up to that crest, they thought they were coming right up on the rim, but they weren't -- and boy, did they sound surprised!

At that point, Shepard estimated it would take another half hour to get to the actual ridge crest, showing how far they had overestimated their previous progress.

Shepard thought they were approaching the rim directly from the west, while Mitchell more correctly thought they were approaching the ridge crest to the south of the crater rim. When, about 20 minutes after Shepard estimated another half hour, they reached the actual rim crest, they were about 60m S-SW of the rim. They walked to the very middle of the ridge crest, about 50m directly south of the rim, and then walked back N-NE another 10-15m to reach a boulder field about 40M from the actual rim. After 10 minutes of sampling, they had to head back because of walkback oxygen and water restraints. (All told, they were about 1.1 or 1.2 km away from the LM at that point.)

The reason the crater rim was invisible was that the near rim was higher in elevation, by about 5m, than the far rim, so the near rim simply made up what looked like a ridge crest. It was really impossible to tell that Cone Crater really *did* drop off right beyond that one crest, and that crest didn't look all that much closer or farther away than most of the rest of the horizon.

Oh, and there were two cases of Scotch at stake -- one for reaching the rim of Cone, and another for carrying the MET (the "rickshaw" they used as a tool carrier) all the way up to the top. They won the latter, since they carried the MET all the way (at one point literally carrying it off the ground when the regolith got too bumpy), and the former was ceded to them after postflight analysis showed just how close to the rim they came.

-the other Doug

Actually, no. Keeping a human crew alive and well is probably easier on the surface than in orbit. At least, it's easier assuming you'll be able to use Martian resources to support the manned crew.

For example, if there *is* a lot of ice easily available to relatively simple equipment, a crew can use Martian water for drinking, washing and food cultivation, and (through electrolysis) to provide oxygen for breathing. They can also use Martian water and elements in Martian rocks to make rocket fuel to get them back home.

Lugging all the Martian resources you want to use all the way up to Mars orbit will be more difficult and probably a good deal more expensive. Most expensive of all is bringing everything you need from Earth.

Biocontamination issues aside, a maned Mars landing is probably going to be easier and cheaper than a manned orbital mission.

-the other Doug

I'm not Doug, but, um... I *am* Doug (the other one), and I can answer your question...

On Apollo 14 (as on most of the other moon landings), the lack of atmosphere made distant objects look closer than they really were to the moonwalking astronauts. Shepard and Mitchell mis-estimated their position almost continually while trying to reach the rim of Cone Crater, which lies upon the summit of Cone Ridge.

In the end, they had to walk a good 40 minutes longer than they thought they would have to just to get there, and they were all of 40 meters away from the rim and couldn't see it. So they sampled boulders 40 meters from the rim, and headed back -- all the while having no clue whatsoever where they had actually gone and how close they had actually come to their goal.

I think Doug was just saying that your sense of distance seems about on par with Shepard and Mitchell's...

-the other Doug

Low lunar orbits can be *very* unstable -- like on the matter of days to weeks. Apollo 15 was inserted into its descent orbit (60 x 9 nmi.) on the second rev after LOI, and roughly 18 hours later the perilune had descended from 50,000 feet to 37,000 feet... and dropping. The 15 crew had to perform a bail-out burn very early on PDI day to increase the perilune before the landing could proceed.

Even the "mid-height" lunar orbits that the Apollo CSMs flew weren't all that stable. The Apollo 16 subsatellite was released from the standard CSM orbit (they canceled a shaping burn designed to put the subsatellite into a more stable, somewhat higher orbit), and it fell ou of orbit after only six weeks.

The only lunar orbits that are stable over a long period of time are those that are propulsively maintained... *smile*...

-the other Doug

If you look closely at the super-hi-res images of the area, you can see that the evaporite outcrops tend to break up the dunes. It's a little circuitous, but it looks like Oppy will be able to chart a course through pretty flat ground.

I don't think Oppy is going to find a lot of problems in trafficability yet. I think that Spirit is definitely going to be traveling rougher ground than Oppy for some time to come, and that's got to be rougher on the wheels and the associated mobility systems. So, I think the odds are pretty good that Spirit will be the first of the two immobilized. But immobilized is not necessarily dead...

-the other Doug

It looks like Erebus' walls are still partially intact along some arcs of the old circle. I think you're right, the crater itself looks completely filled in, such that the landform is going to look from the ground like a very low ringwall sticking up a foot or two from the plains.

It may not give us any deeper layering into the evaporite, but the ringwall of Erebus *is* the very rim of a crater roughly half the size of Victoria. Certainly a much larger impact structure than we've visited thus far. So it's possible that some of the rocks exposed in and around the ringwall will come from *much* deeper than we've yet seen.

Of course, those rocks may well be the basalts that underlied the sea and provided a base for the evaporite layer... we'll just have to wait and see.

In any event, it seems to me that there *may* be a Burn's Cliff sticking right out of the sand up there at Erebus, right within easy reach all along its height and breadth... I can't wait to see!

-the other Doug

Looks really good, Tman!

It's pretty obvious that both Viking and Voyager are a little smaller than Eagle -- I can't see the landing platform fitting inside either V or V with room for Oppy to roll off without driving halfway out.

Voyager is also obviously older than Viking. This is a really, really good example of how the ejecta blankets of craters of this size erode -- notice how here, around Voyager, the ejecta blocks are still visible around the crater, but they are efficiently flatted down. They still form a slight bit of relief (a small mound that the crater sits neatly amidst), but the blocks themselves have been worn down to a nearly flat surface. Note how nice and even Oppy's tracks are as they run through the ejecta blocks -- that's a flat surface.

Viking looked exactly like this *except* that the blocks around Viking are still partially intact.

This evaporite erodes down very, very efficiently, doesn't it? No matter what landforms were created within it, it seems to erode right down to flat fairly quickly... so it doesn't retain its structures above-ground all that well. The only thing it seems to retain is holes.

Makes you wonder what caused the cracks (i.e., Anatolia, etc.). Are they evaporation cracking of the surface, or are they erosional? Seeing how easy it is to erode these rocks, erosion might be a little more likely than I had thought.

-the other Doug

I've done some extensive Googling, and can't find a single reference to Odyssey going into safe mode this last week. Nothing whatsoever at any of the NASA or JPL websites. The only thing Google picks up on search phrases "Odyssey" and "safe mode" are articles on the spacecraft being affected by the huge solar flares of a couple of years ago.

So, 1) does anyone know the real story and what the Odyssey team thinks might have happened, and 2) why the heck isn't *anyone* reporting on this?

-the other Doug

The cruise stage, not being particularly aerodynamic, would have broken up into a lot of pieces at max deceleration. How far the individual pieces travel depends on their ratio of mass vs. drag.

The least massive pieces with the greatest surface area would have burned up, contributing a little metal to the global aerosol dust. Beyond a certain threshhold of this ratio (not necessarily the lightest or heaviest pieces, just beyond a certain point in the mass/drag ratio), a piece will survive max heating and reach the ground.

Since each piece has a different mass/drag ratio, and since that ratio changes dynamically as the air thickens, speed slows and material ablates, the pieces all separate and form a debris footprint. That footprint will almost always fall *short* of a protected entry body (like the heatshield-protected capsule) because, in the process of breaking up, the total mass of the unprotected body (in this case, the cruise stage) suddenly presents tens of times more surface area to the atmosphere it's ramming into than the single, unified body had presented. So the mass/drag ratio shifts dramatically towards the drag side of the equation, and all of the individual pieces fall uprange of the protected capsule.

Now, if the stage contained a nice cylindrical fuel tank that was both relatively massive (representing a fair fraction of the total mass of the stage), and that tank were made of a heat-resistant metal like beryllium, the tank (being a nice aerodynamic shape) would fly on to the farthest downrange end of the debris footprint. But even so, its mass/drag ratio profile would still probably have it falling uprange of the landing site.

-the other Doug

There are a couple of different landforms, here. There is what I think of as the true etched terrain, which has ridges of what look like evaporite outcrop surrounded by duneform-controlled patterns of dark and light sand. What lies directly between Oppy right now and its target at Erebus doesn't seem to have any actual outcrop (at least not any more than you would see out on the flat plains) -- it's just got what looks like duneforms of lighter sand overlying the dark, concretion-derived sand layer. As we get closer to Erebus and the ancient crater cluster to its south, some of the duning looks a *lot* lighter.

It's going to be very interesting to take a close look at the lighter sand in those dunes as we head south to Erebus. I would have to think there will be some significant differences in minerology between this lighter sand and the soils we've seen thus far.

-the other Doug

There are a lot of rocks in the solar system in orbits that intersect in all sorts of different ways. Some meteors approach Mars relatively slowly and are slowed to a relatively slow speed (I don't have an exact figure, but possibly as slow as a few hundred miles per hour) by the atmosphere.

Now, I doubt that this rock just entered and plopped down gently on the ground. I'd bet that a rather bigger rock landed as slowly as any meteor every lands on Mars somewhere within a km or two and this fragment was ejected relatively whole and undamaged. It probably bounced a time or two before landing in its present position, looking for all the world like it was just set down there by a giant's hand...

"Slow" impacts are relatively rare, I'm sure, but they do happen. I remember seeing an MGS high-res image of a Martian crater that literally looked like a long trench. You could see the impactor lying in a heap at the end of the trench, with dirt just splayed out from it like a bulldozer had shoved it out. The thing had obviously hit at a very low angle to the ground. The impactor must have been a good 5-6 feet across (it was two pixels or so wide, IIRC, on an image that was rated something like 1-2m per pixel resolution) , and the crater was only about three or four times wider than the rock that made it. Had that same rock impacted at the average velocity of impactors on Mars, the crater would probably have been a LOT larger.

(Yes, it might have been a secondary, but the dirt it excavated was a *lot* darker than the dust-covered soil around it, making it look very, very fresh. I guess it's possible there was a large enough impact relatively recently and nearby enough to have made a secondary like this, but I think you really could see this kind of crater morphology in a slowest-possible-speed primary impact.)

-the other Doug

Maybe it will. If my theory is correct, we're just now appraching the edge of the ejecta blankets from the ancient crater cluster. The problem, of course, is that the ejecta blankets have been highly degraded and modified since they were emplaced. I would guess, from the way the terrain looks, that the best shot for seeing exposed ridges of actual ejecta would be in the lightest patches of what looks like outcrop within the etched terrain.

-the other Doug

Oh, I don't know -- if they do, indeed, delay MSL to 2011 and send two of them (as is being discussed), it might make sense to send one to Meridiani Planum. It is pretty well proven that Meridiani's landforms were shaped by standing water, and if the MSL rovers are looking for signs of past life, this would be a pretty good spot to start looking.

Also, Meridiani provides a pretty large stretch of absolutely flat "landing strip" for whatever landing system MSL ends up using. You could do worse than land near the edge of the extremely flat plains at Meridiani and drive off to more interesting-looking targets from there... If they do that, they might well land somewhere that Oppy has scoped out for them, give Oppy a once-over, and then drive off to some of the *really* interesting big craters and ejecta blankets to the south of Oppy's landing ellipse.

Whatever part of Mars they end up targeting for MSL, they're probably going to look at places that have good landing conditions closeby to interesting science targets, so the rovers can land on flat, level, relatively rock-free (if possibly boring) ground and then drive to more interesting spots.

-the other Doug

Makes you appreciate why Squyres, in one Q&A session, said that his number one priority for "what to do different" on future missions is to have a bigger pipe for getting data back to Earth.

Heck -- my cable modem provides me 5 Megabits per *second*. At that rate, I can download 300 Megabits in about one minute.

How much coax cable would it take to set up the MERs with RoadRunner service, anyway...?



-the other Doug