Looks like lots of chunks lying around. Its going to be very interesting to see how they have interacted with the sand du, er ripples. Which leads me to another thought...

There have been lots of discussions on the tiny craters, etc, and whether they are caused by sapping or are tiny impact craters. I've been puzzling over this for ages (I'm not a geologist, btw). It seems to me that the dunes must be static now, otherwise the wind that we know blows over the plains would fill in the craters by moving the sand. They must have been mobile at some point, otherwise they wouldn't have the wind-sculpted shapes. This means they *must* have been mobile at one point.

I'm finding it hard to understand how slow hardening could result in preservation of the ripple shapes, so it ocurred to me that it might not have been so slow. We know that the apron of Victoria is splash-like, which might imply water. So perhaps the impact released a cloud of water vapour that interacted with the very fine, very dry sand, and essentially fixed it in place.

Am I talking nonsense?

Chris

That's an interesting speculation, Chris. I think it's always important to keep in mind that some geologic processes happen very rapidly while others, the ones we usually consider, act very slowly.

There are others on this board who know more about this subject than I, but since I seem to be the first responder, I'll offer an opinion. Given the heat generated at an impact and the low atmosphereic pressure, I would expect that most of the water melted during an impact would quickly vaporize, or freeze and sublimate rather than precipitate as rain or mist. But then again, even if an impact resulted in a heavy frost, that small amount of water might help form a duricrust.

Let's see what the experts have to say.

It is also possible that the dunes formed when the atmosphere was denser, and better able to propel the particles they are made of.

Let's just say Mars has been fairly 'samey' in terms of condition for...shall we say 3GY?

And the air, because it's so thin, can move an average particle of soil perhaps 1cm per year

Over that 3GY - that soil particle could have travelled 30,000 km

Doug

Actually, the du er, ripples are armoured with larger particles that seem to have been left as a protective residuum, after their last movement...the fine and moveable stuff has been removed by the wind, leaving a layer of larger, mostly unmoveable clasts that protect the underlying mixture. I seem to remember reading that the current winds on Meridiani seasonally reverse, from the NW to the SE. I hope I got that correctly. But I do think that current thinking is that the current ripples (no pun intended), are essentially static. Either stonger or more dense winds would be required to significantly change their orientation.

I'm not sure that they are billions of years old. That seems doubtful. They are somewhat old. Since the ripple orientation has been remarkably constant from the start, it would be difficult to ascribe an effect from Victoria's creation as significant, though it might be interesting to look for such an effect as we approach her.

Oh - I wasn't saying they were that old - but it was suggested that the air is not thick enough to make such things....but over a very long time period, it's MORE than strong engouh.

Doug

I wonder. If I push something, not quite hard enough to move it, it doesn't matter if I do it for 1 hour or 3GY, it still won't move. The larger grains being slowly worn away by the very small stuff, on the other hand, will very slowly cause changes.

Chris

Well, I'm not so sure the time period was long at all. From one perspective it might have all happened rather quickly - then sort of 'froze' in its current state after only a few years. We'll never know for sure - despite what some would lead us to believe.

If this was (and it appears to be) the bottom of a sea that more or less dried up at some point - what we see could easily have been created by wind-blown sea water prior to final evaporation. How long ago could such a sea have existed? We don't know for certain... it could have been there a thousand years ago, and everything could look as it does today.

Wind obviously has had an effect, but to what extent it now effects the area seems rather settled - lighter winds have moved smaller particles, leaving behind the heavier... but still more or less in the same configuration (possible) that water left it in.

But, if Oppy runs into 80-90MPH winds - such a theory goes pooof.

Well - 12m/s as measured by Pathfinder, I've seen 25.2m/s with V1 data, 20.1 with V2 data - (27, 56, 45 MPH respectively )

Give how much movement we saw around the areas where the wheels dumped bright material after leaving Purgatory, and how degraded 180ish-sol-old tracks were on the way out of Endurance....I find it hard to imagine that over any lengthy period, say a century, one wouldn't be able measure movement in some of this.

Doug

Sattrackpro,

Sorry, I'm going slightly off-thread here.

What I think you are implying is that these dunes or ripples were created underwater aeons ago, but forgive me if I'm wrong. I would agree that the underlying evaporites were formed underwater (Opportunity has plenty of evidence of that). However, digging back to sedimentology lessons from my geology degree (many years ago!) the overlying dunes (and I prefer to call them that rather than ripples) are too large to have been formed underwater. These are most likely completely aeolian deposits (i.e. wind-formed) on top of the older evaporite pavement. Submarine sediments tend to form small-scale ripples on the scale of a few centimeters (much like the festoons observed in the outcrops), rather than the 2-3 metres dunes we see.

Whilst the air may be thinner on Mars and therefore less able to move grains, we mustn't forget that the gravity is much weaker here, so it doesn't take as much inertia to get a grain moving.

I find it hard to believe that these dunes were formed aeons ago and have been frozen in place. I don't have any evidence to give you other than my geologists intuition that tells me that these dunes are fresh and active (moving on the scale of months and years rather than millenia). If they were really old, gravity, diurnal temperature changes and weak winds would have made them collapse to a large extent. As it is they look pristine.

Comments welcome.

Castor

Castor:

I take the opposite view on dune ages (and yes, they look like 'dunes' to me, too!). Mars is a very static place compared to Earth, with hardly any active erosional processes, at least on familiar timescales. The crusty dune surfaces all suggest a frozen sea of very fine sand, with a little light spray of dust here and there. Add in the suggestions of quite dramatic climate changes every few tens of millions of years due to orbital effects and polar wandering and I have to opt for 'punctuated equilibrium' as the Martian norm: long periods of almost no change and brief active windows of activity. Dune ages of up to 100 million years would not surprise me at all.

That's my take on it, anyway - I think we are easily misled by the familiarity of Mars, which really is an unEarthly place!

Bob Shaw

Perhaps I should have created a new thread for this....

Chris

One hates to interrupt a pair of Sassenachs locked in scientific debate (native Scots must be gathering around in disapproving fascination). But I would like to interject here the global dust storm phenomena, which, while doubtless divergent from similar dust storms on earth, certainly do occur on "familiar timescales", and must leave in their wake some recognizable signs. Can anyone look around our MERs and point to features, among the ancient 'dripples', left by the last storm, or the last million storms?

Speaking as a non-expert who has witnessed, along with everyone else here, Spirit's brush with a semi-global dust storm, it seems the biggest feature left by such storms is a very gradual growing layer of dust which is redistributed by local gusts and dust devils.

In a nutshell, Cents, that might be the story, but it certainly trivializes the sense of a "storm" to what might more accurately be called a "dust fog". (I never heard about how typical of dust storms Oppy's brush was.) Certainly the Hollywood rendition of a Saharan sand storm, where heroes and camels stagger around, narrowly avoiding burial alive, is an inappropriate analogy. Current eolian erosion on Mars must be gentler than a baby's kiss.

In a theoretical sense, like we use in our basic physics force diagrams that's true. In the real world however, there are thousands of otherwise neglected forces that come into play over longer periods of time -- especially 3GY.

In the case of a pebble resting on a larger rock, a force applied insufficent to cause motion does in fact create pressure between the rock and it's contact surface. That pressure over a long period of time could be enough to create erosion, for lack of a better word. We can't see it, but the energy transferred from the constant force DOES have an effect on the grains and molecules of the pebble, as well as the larger rock it's sitting on, and it can add up over time. The microscopic lumps and bumps on the surface that create the static resitance to motion, will eventually crumble due to the prolonged application of a force on them. The pebble then moves some distance, however small, and the process begins again.

Shaka:

Yup. And I'll bet that although over a long timescale you do get a lot of dust flying about, it's the *same* dust which gets blown around, with much of the top few millimetres of the soil effectively cemented in place, only being moved when erosion gets turned on. So yes, there's current movement of verrrrrrry fine dust, but it doesn't do much other than get blown about.

Bob Shaw

O.K., Bob, this could be the reality of Mars. But I hope you can sympathize with the incredulity of born-and-bred Earthlings like Castor and I, that this "wave-tossed sea of sand" is in fact a museum diorama in a dusty glass case. Looking through the MOC images we are constantly struck by the evidence for vast periods of erosion of native rocks, deposition into uncounted strata of sedimentary products, and erosion of those strata over ages more. Meteors crater the landscape, the craters are eroded, buried, and eventually, after how many more ages, exhumed again and eroded some more, and then...? We see uncountable mesas and valleys, plateaus and basins, ostensible rivers and seas. And we are then told that this all happened in the Noachian-Hesperian, and since then...next to nothing.
In the British Museum we can inspect an Egyptian mummy in a glass case, and try to imagine this object as a living, scheming, political animal of the third millenium B.C. It's a stretch, but we manage it. It's even more of a stretch to journey across the fourth planet in the solar system and accept that it's only a museum display.

Shaka:

And then the climate changes, and things start up, before again shutting down for umpteen million years! Do that over a long enough timescale and things *do* happen, even on Mars. The surface features of Earth are young, young, young - the post-glacial landscapes where many of us live are *younger* than modern humans, though the rocks and underlying geology are (quite) old. Our perceptions of Mars are based on what we see on Earth, and I reckon that they mislead us unless we are very cautious.

Bob Shaw

They indeed do ~look~ pristine - and to some extent, I must agree with you - there's more to the real story than we've heard or read.

I think the 'real story' is quite a bit different than many think - part of that may be that this 'old sea bed' may not be so old after all. Another part of it is that the atmosphere of Mars has changed radically (and is said to be accelerating) in recent times... just look at the rate it is disappearing now. Just a few hundred years ago it was much denser, and probably supported more radical weather (winds) than we see now.

We have this propensity to deem everything happening on Mars on a time and geological scale much the same as that of earth, and I think that's perhaps at the root of some poor thinking. Suppose, for example, that this sea had become subjected to hurricane force winds in a much denser atmosphere. It isn't difficult to see virtually the exact kind of terrain we see today, since we can see so-called 'mega-ripples' - actual large sand waveforms on the seabed near the Sable Island Bank. The waveform trough to crest measurements there, and in other places on earth, run between 5m and 10m - close to what is around Oppy.

Maybe it did the same on Mars - back when - maybe it didn't. But, there are 'earthly' examples of almost identical underwater waveforms - in the here and now. It might be a stretch to think the same would happen on Mars - but... similar forces just might create similar results.

I think we are seeing a fundamental difference between historical processes on Earth and Mars. On Earth we see that tectonics, erosion, weathering and deposition for the most part occurred in a similar manner a thousand-million years ago as it occurs today. I can look at a series of deltaic facies 300 million years old and know that I can go to the Mississippi River delta and see the same lithologies and processes next week.

On Mars, my suspicion is that there is less "uniformitarianism" (uniformity) in those geologic processes and that the Mars we see today is much different than the Mars that existed a hundred-thousand years ago. In a way, we may be looking more at catastrophic processes as opposed to uniform processes on Mars (over periods of millions of years). I suspect that there is a large amount of Mar's atmosphere (carbon dioxide) locked up in the polar regions and the density of the atmosphere depends on the state of this CO2 source/sink. Currently there is the majority of the atmosphere locked up at the poles and atmospheric pressure is low and conditions are calm. In a few thousand years the solid CO2 may be released back to the atmosphere and we'll have a higher density and more active atmosphere.

I guess I'd say more "cyclic" than "catastrophic"; the latter term has connotations.

More later...

--Bill

Bill:

As I said, 'punctuated equilibrium' - but I think the periods between activity are longer than a mere few tens of thousands of years! And your point about current processes *not* being the same as those seen in the geological record is very true - essentially, at the moment there's nowt going on to speak of, but we can see the signs of past activity everywhere. But 'past' really means 'past'!

This is *not* the way things work on Earth!

Bob Shaw

One thing about the dust that is easy to see is the 1 or 2 mm of it on the Rovers, this has deposited in only 2 years, after 2 million years you would have a lot more dust laying on the Rovers, all be it some of it may subsequently be blown off at some time.

There is a lot of dust on the rovers in terms of the reduction in the amount of power they can generate but they are both currently running at around 60% of their original value so we're talking about a couple of microns depth not mm. It's still noticable and clearly really fine dust moves around a lot but the larger dust and sand scale particles are an awful lot harder to shift when your atmosphere is only 1-2% as dense as earths.

It's not just dust on the rovers, the MI images of the very front of the solar array show some actually fairly large grains up there as well....sand sized grains...not just tiny tiny particles of dust.

http://marsrovers.jpl.nasa.gov/gallery/all...IIP2979M2M1.JPG

I think some of you are far to quick dismiss the martian wind as having near zero ability to move dust or sand. Given that we're seing such large particles up on the array deck, quite rapid erosion of rover tracks, dust tails formed by clod deposition....I'd argue that these dunes are an active formation. Not fast...but active. You can rule out water formation for them, they are far too large: consider the cross bedding - that was indicitive of the sort of ripple size one would get from moving water, not these metre scale dunes. Compared cross bedding at the lower unit at Burns Cliff ( very large, wind induced ) and Eagle crater ( very small, water induced ).

Consider Erebus crater - almost entirely filled in by sand and dust...the VERY large dune formations on it's Northern Rim..... wind can, and evidently DOES move thus stuff about.

Yes - it's roughly 1.5% of terrestrial atmospheric density - but it's also 1/3rd G. I'm not sure if the maths works out - but you're talking just shy of 5% the material mobility of Earth...I think that's quite enough, and clearly I'm not alone

http://www.news.cornell.edu/Chronicle/99/2...Mars_dunes.html

http://barsoom.msss.com/mars_images/moc/11...2306/index.html

http://www.msss.com/mars_images/moc/top102_Dec98_rel/dunes/

http://www.msss.com/mars_images/moc/2004/08/05/

Doug

Hopefully when HiRise is up and running we'll be able to actually study the tracks over time. Even the MGS cPROTO images showed the tracks from Eagle to Endurance. Now we have a great series of documented ages of the various tracks which we can watch until they disappear. The assorted messes we've made such as the trenching at Purgatory should be around longest of all.

I'd be interested in seeing what Eagle Crater looks like now.

The wind speed is another factor, and Mars tends to beat Earth in that regard, but it's a trickier factor to measure, since you'd have to integrate over time. The ~maximum may be more interesting, and it looks like a random spot anywhere we've had a lander can count on encountering a dust devil in a couple years' time. That's certainly not true on Earth, my Midwestern cousin's bad luck withstanding (and the roof of her house notwithstanding! Two tornados since she's lived in the same house!). Dust devils seems to have winds of 30 m/s, while a pretty bad storm gust by the standards of most places on Earth is 20 m/s.

Wind will exert a force proportional to speed^2, so you might give another factor of 2 for Mars, but you also want to integrate over the realm of movable "targets". If one planet were all boulders, modest winds would never move anything. Mars has more loose dust than Earth -- certainly on average, when you think about our oceans and our forests. That may be a factor of 6 or more, 60 as far as I know, so we end up with Mars having something like 60%-600% the mobility of Earth, based on some numbers I pull from my drawer of estimates.

The big difference is that Earth has lots of water-driven mobility which will eventually crumble mountains and craters into nothingness. But in the short run, at the low end of the target-mass, Mars is a very dust-moving place. The greatest mitigating factor is probably that dust is in many cases moving onto parcels of surface that just had their own dust swept -- as on Earth, it rains on the ocean. The effective mobility we can see, then, is a lot less than if you integrate over how many grains are moved.

~ = Over a few years time. One bad storm in geological time can only move so much dust.

Doug, I'll agree with you wholeheartedly that these dunes are active and not a frozen-in-time museum piece. As seen, and as you note, by the changes observed in the Rover's tracks, deposition on the Rovers and other features we have observed along the way. Slow by Terran standards, but far from dead.

Even light force will act given enough time. If you hit a piece of glass with a hammer, it will shatter. If you stand a piece of glass against the wall, over centuries it will flow as a supercooled liquid in respose to gravity.

Even though I'm a geologist and accustomed to thinking in aeons, I have great trouble visualizing timeframes of millions of years for some of these minor processes. The little intuitive voice in the back of my head suggests hundreds or thousands of years, give-or-take.

We're on the right track, though.

--Bill

Actually, that seems to be a myth, at least on macroscopic scales:

http://www.glassnotes.com/WindowPanes.html

And a steady 1 m/s dry 6 mB wind might just about never move or even erode a large boulder. In principle, it is possible for a steady object to resist eons of light force. For example, craters on the Moon stand against a steady light force of gravity. If they will ever be pulled down to the plains, it's going to take considerably more than a few eons.

However - we know that Martian wind isn't slow and steady - there are times when it's fairly harsh (harsh enough to clear much of the dust from a rover, and significantly degrade rover tracks in a single night)

We also know that the winds are occasionally strong enough to make a rover move. Not a lot...but some of the DD movies show about a pixel of shift due to high winds rocking the rover.

Doug

As I recall, one theory had the large grains on the rover panels being formed by dust clumping during repeated frost/thaw events. Is it possible to determine if any of the grains are actual sand grains, or if they are all clumped dust?

There are several discreet sand sized particles sat on there around the wires - they're unmissable. Not clumps of the dust ( they would be the same shade as the remaining dust on the deck ) and indeed they're hidden in wind 'shadow' of various components.

Doug

Doug,

Thanks for digging out these references and re-iterating some of my points, particularly about the weaker gravity on Mars. You're not alone in thinking the dunes are an active formation. I found the first reference quite interesting:

"The winds on Mars appear strong enough to transport sand only at certain times of the year. A major reason is the planet's eccentric orbit, which produces strong winds primarily when Mars is closest to the sun. Strong winds also are due to the fact that a third of the atmosphere falls out of the carbon dioxide polar caps, and the motion of the gas creates very strong, highly seasonal and one-directional winds at high latitudes.

Until now, said Thomas, the model of the Mars atmosphere "was one of winds moving sand not very often and then pretty much in one direction at a particular spot -- and that's exactly what we are seeing." On a broad level, he said, modelers of the Martian atmosphere have the picture right."

I know Opportunity has been here for more than a Martian year, but it is still possible that we haven't yet witnessed the strong winds that might be capable of moving these dunes.

I take Bill's point though about uniformitarianism not being the same on Mars and what others have said about our Earth-centric views of geomorphological processes.

Sounds like all this fascinating discussion should be moved to a new thread.

Castor

No, no, no!

You guys have it *all* wrong!

The truth regarding cleaning/deposition events and dust movement is now out...

Bob Shaw

We certainly haven't seen anything close to the conditions of a complete global storm. Spirit landed just after a fairly large storm and we have two regional events since they landed, one of which was big enough to be seen clearly from earth. The last major planetwide storm was in July 2001 if I recall correctly.

Doug's link clearly shows to me that we are seeing evidence of proper dust sized particles being lofted about regularly not just micron scale dust that I thought was the case. Even though the picture only shows a few mini drifts on the sheltered parts of the rover deck that does indicate that a lot more dust has probably landed and moved on over the course of the last 2.5 years. Say we are seeing motion of a single layer of dust every two years then you could (in theory) completely build up or deplete a 30cm dune in 150-200 years without any change in overall conditions. Now grain sorting, surface cementation and the dynamics of dune formation probably rubbish that particular number but the possibility of this terrain being quite dynamic over human familiar time scales is interesting.

>Actually, that seems to be a myth, at least on macroscopic scales:

Interesting. So much for that urban legend.

But still, there are solids that are brittle under sharp force but plastic under steady force. Water ice, for example.

--Bill

Or the Ig-Nobel-prize-winning pitch drop experiment:
http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml

Bob,
Are you gona use this image (even a little bit reworked each time) on ALL traits ?

Hey, that would be a pretty cool demo to do on a large scale...Get a large glass dome made in a park or something, and put in a giant funnel of pitch and watch it drip!

We are talking about the Mars that has recurring global dust storms covering large parts of the planet, the Mars where Spirit has imaged dozens of large dust devils, aren't we? - It is quite obvious IMHO that we are talking about a very active atmosphere shifting surface material around quite thoroughly. I'd say the dune pattern Oppy travels through is shifting in a time span of years, not centuries, millenia or eons...

Hey, it was a *lot* reworked - last time it was just a grab!

Bob Shaw

Here is my 2 cents (pence) worth. Doug, I am not trying to single you out in this debate, but as is often the case, you are in the thick of it and have zeroed in on several of the key points.

I have no doubt that current Martian winds can move sand and dust grains. But the issue is, can they now move these dunes/drifts/ripples. Regardless of some small-scale features that we have seen move, the fact still remains that the main features we see both in Meridiani and Gusev seem not to be moving since man has been observing them. That is the reason the Meridiani ripples and those in Gusev appear in the same location to the rover's eyes as they have appeared to the MOC's eye in images taken years earlier and later. There was an earlier discussion which I can't find, where some compared MOC images taken over the years of the same area. No discernible movement was discovered. That is one reason why the MOC imagery has been so useful in the fine route maps produced by members here.

Recently I have been beating the drum about the "armored" nature of these things. I didn't first notice that, although I can now see what they are talking about. This is something that was mentioned by several researchers at LPSC this year. Evidence was presented showing that the surface of the Meridiani drifts are covered with larger clasts than commonly exist within them. I think that is pretty clear, if you think about the MIs and close-up pancams we've seen from Meridiani. More difficult to see is the armoring of the ripples in Gusev, but they have looked closely at that, too, and presented good images showing larger sand grains and granules forming a protective layer on top of otherwise more finely grained ripples.

...I think wind can, and evidently HAS moved this stuff about.

I'm not sure we're ALL talking of the same thing i.e. what "move" mean! I'm not able to explain this scientificaly but I'll compare this to clouds formation in the mountains. There you can see clouds forming from "nowhere" then moving in the wind direction then next cloud forming exactly in the same place etc...
I believe that the general structure of each individual "dune" stay in the SAME place while grains /particules are actualy moving. What about that?

That would go against the "tiger stripes" we're seeing on one side of most of the dune ridges. From what I've seen, signs point to the dark stripes containing a significant fraction of basaltic origin dust, including olivine, the light stripes with lower content of the basaltic origin dust. How did these layers form? How have these layers been preserved if the dunes are active?

Dunes with obvious layers can be very helpful in assessing the depositional history of an area.

In some areas, like the serpentine dunes on the top of Husband Hill, certainly.

Bob Shaw

Ok, I hope everyone can forgive me for one more comment. I'll try to keep it as short as possible, but having heard many making this argument, even someone on the MER team who probably started the whole thing, I just HAD to comment.

I need to make one thing perfectly clear from the start. I completely agreee with Doug and others who have pointed out that the surface ripples have nothing to do with water, and for many reasons are beyond a doubt, are formed by wind. But using only a scale difference to distinguish between sub-aerial and sub-aqueous bed forms is wrong. The devil is in the details. There are many examples of elongated bedforms of small to intermediate to large scales that are formed under water. Sand bars, various types of shoals, and sand-waves are just a few. There are several images and descriptions of some such things on two pages here.

I saw a synergy between this and previous comments about uniformitarianism/catastrophism in geology that I could not resist. I think it's a good story. Early in the previous century there were some truly magnificent elongated bedforms brought to the forefront of the uniformitarianism-entrenched geological establishment by a young upstart named J. Harlan Bretz. I'm sure that name will ring a bell with some of the older geologists around here. I don't know if the story is still told in modern curricula, but long ago, when I was in school, it was considered important geologic history. I'm getting all nostalgic, now.

Anyway, he saw evidence in Eastern Washington state for huge glacial floods that created all kinds of fantastical things in a region he called the "channeled scablands." Among those things were what he termed mega-ripples, and are otherwise referred to as giant ripples. They were up to 10-15 meters tall. Major early 20th century flame wars erupted when he published his observations. In the end, Bretz came out as the hero and he will always be recognized as a giant in the history of geology.

But in another area, another geologist named Wegener was wondering why some of the edges of certain continents fit together so well, like puzzle pieces.

Later in the century, observations by other young upstarts, noticing continental drift evidence, re-ignited the flame wars. They have now long been vindicated, as were Bretz and Wegener. Today, everyone can make nearly realtime observations on another planet via the rovers and orbiters. That's where UMSF comes in. The "next young upstart" line begins right over there... But I digress.

I've "borrowed" a couple of images of these mega-ripples that give an impression of their scale. Large, ripple-like features can be created by water. But as I initially mentioned, they are not like the Meridiani ripples. Those images should be ascribed to the following pages, where I found them.

http://www.kidscosmos.org/kid-stuff/kids-c...-scablands.html
http://www.ndsu.edu/instruct/schwert/geosc...lumbia_plateau/

Oh, and this link has a picture of my hero, and a decent description of the story.
http://en.wikipedia.org/wiki/J._Harlan_Bretz

What a great comment! Thanks for sharing.

The channeled scablands are one of the many exceptions to the uniformitarianism principle and shows that things are not always as they were. Although I mention this principle as frequently as anybody, I do mean it in the general sense: weathering, erosion, transportation, deposition and lithification yesterday are similar to the processes we see today. But the release of the water that formed the Scablands was a non-usual event, just as the winds that formed the Meridiani plain ripples was outside of the conditions we see now on Mars. But it is quite clear that this landform is aeolian; the task ahead is understanding what the conditions were that produced the required energy to give what we see.

But I can guarantee that the Mars we see today is not like the Mars that was yesterday or will be tororrow.

--Bill




PS-- one of my heroes is J. Tuzo Wilson.

My hero, Gene Shoemaker, the "God of Planetology" as one researcher refered to him once, took a trip down the grand canyon in the early 70's. They located and duplicated most of the original photographic stations of Powell during the first trip down the Colorado through the canyon nearly 100 years earlier. Comparison of the images taken over that time interval show that most detectable changes were small, sharply defined "local catastrophies" (and changes in vegetation).

I knew Gene, though not really well, having internned two summers at USGS Flagstaff. Losing him to a car accident while impact crater hunting in Australia was like losing a member of family. It still hurts.

Moving dune related posts here so the discussion can be found after Oppy has moved past Beagle Crater

Thanks.