MER search for dust devils - hoping for a rover's eye view...

atomoid · 2004-04-23 02:31:41

So Spirit is "fishing for dust devils":http://www.msnbc.msn.com/id/4790474/]article:

Spirit's cameras are scanning the skies to do “dust devil fishing": seeking time-lapse images of Martian mini-tornadoes. When captured by cameras on probes orbiting Mars, these mini-tornadoes show up as tall, thin white clouds, casting a shadow and leaving a dark trace on the ground as they move. In Spirit’s cameras, nothing has shown up so far but the odds are that persistence will pay off.

And according to http://www.gsfc.nasa.gov/topstory/2004/ … .html]this interesting article:

These Martian dust devils dwarf the 5- to 10-meter terrestrial ones and can be greater than 500 meters in diameter and several thousand meters high... ...If Martian dust grains have a variety of sizes and compositions, dust devils on Mars should become electrified in the same way as their particles rub against each other... ...Since the Martian atmosphere is extremely dry, the charging is expected to be strong, as there will be few atmospheric water molecules to steal charge from the dust grains. However, since the density of the Martian atmosphere is much lower than Earth's, the near-surface electrical conductivity of the Martian atmosphere is expected to be 100 times higher. A Martian dust devil will therefore take longer to fully charge, since the increased atmospheric conductivity draws charge away from Martian dust grains.

...not sure if this means that theres more voltage getting grounded into the soil or not, but if electricity can be an impetus on the coalescence or formation of organic molecules, might this perhaps be supportive of processes leading to life? but is the 'zap' strong enough? note the image depicts an http://www.gsfc.nasa.gov/gsfc/spacesci/ … electrical discharge glow. So we've got water and lots of minerals in the soil, UV and radiation probably creating all sorts of radicals at the surface and some static electrical stuff going on as well, sounds like if the soup was wet enough something might eventually happen with all those ingredients...

Shaun Barrett · 2004-04-23 05:34:30

Atomoid, I want to say, before I forget, that I just love your signature! :up:
Very amusing! :laugh:

In response to your post about static electricity in martian dust devils, I wonder about soils saturated with brines or even small ponds or marshes of concentrated briny water. Isn't salty water an extremely good electrical conductor? And wouldn't such brines result in the discharge of much of that static in the dust devils into the martian surface?
I'm no expert on electrical activity in rotating currents of dry air; just throwing a few thoughts into the debate in the hope of eliciting wisdom from those better able to comment on a topic which could have serious ramifications for astronauts out on the surface of Mars in bad weather.
???

atomoid · 2004-06-08 20:01:38

Today's http://www.spacedaily.com/news/mars-dus … ml]article on Martian dust devils implies that Pathfinder took some photos! ? ! ? hmmm? anybody know about this?

"At the Pathfinder site during its 83 sol mission, approximately thirty dust devils were either sensed by the pressure drop as they passed over the lander, or were imaged by the Pathfinder camera," says Smith.

REB · 2004-06-10 07:27:06

Here is some data from Pathfinder of a dust devil that passed over the probe;

http://nssdc.gsfc.nasa.gov/planetary/ma … devil.html

Here a picture of another dust devil. I remember reading that it was going down Twin Peaks.

http://www.unr.edu/nevadanews/vol2no118 … 2no118.htm

atomoid · 2004-06-13 18:18:04

very cool, thanks for finding that. i guess thats the best picture from the ground (so far). Pretty amazing nonetheless...

Its hard to say how big it is since the false color might only be showing part of it. They dont say whether the one that was detected by the weather instruments is the same one pictured when it was farther away, probably not...

Shaun Barrett · 2004-12-20 19:48:02

I'm beginning to think that dust on Mars may not be such a major problem after all. Although we've been expecting the MER's electrical power to gradually die from dust accumulation on their solar panels, very little of such an effect has been encountered.

Photos like this one, taken on Sol 329, show parts of Spirit looking essentially dust-free:-

Perhaps, outside of a real dust storm, fines will present only minor difficulties to machinery on future expeditions(?). If the astronauts take precautions during storms, covering up anything vital, then Mars weather might be no more troublesome than desert weather on Earth - maybe less so.

As I've mentioned before, when trips to the Moon were being planned, astronauts were going to disappear into many metres of quicksand-like Moondust, they were going to contract lunar diseases and/or bring them home, and the dust was going to choke up their machines and maybe their lungs as well.
None of the above actually happened.

I think the pro-robotic anti-human exploration lobby is doing a good job of scare-tactic-campaigning when it comes to Mars, too. And it's perfect fodder for the zero-sum Lefties and Luddites, who look for the worst in anything to do with new technology.
???

djellison · 2004-12-21 04:11:41

Spirit is infact very VERY dusty - it's producing only about 400 whrs/sol - Opportunity, however, is almost dust-free and knocking on 950 whrs/sol

No one is quite sure why - but the recent rover deck surveys in L456 by both rovers, and MI images of the edge of the solar arrays are set to hopefully answer that question

Doug

Shaun Barrett · 2004-12-21 04:42:43

Hi Doug.
I understand that the electrical power rating of Spirit is about 400-odd Whrs/Sol and Opportunity's is about 900.
It is assumed that dust is responsible for Spirit's low electrical production but I have no way of knowing for sure, and neither does NASA, it seems.

All I have done is look at the evidence available to me, the pictures from Mars, and check for dust. Maybe it's the resolution of the pictures, I don't know, but I don't seem to be seeing a great deal of the dust purported to be responsible for the problem.

NASA is so at a loss to explain the extraordinary power production of Opportunity that they've even invoked dust-devils as a possible agent to clean the solar panels!
Their next best guess is that water condensation on the panels is causing beading of the dust and freeing up more surface area for insolation.
The fact is, nobody really knows.

I don't like accepting everything at face value just because a NASA scientist tells me so. We're not entirely stupid. We don't need a Doctorate in astrophysics to look at a photograph and decide whether a solar panel is choked with dust or not.
We've been told dust is the explanation for Spirit's poor electrical production but NASA doesn't have an adequate explanation for Opportunity's unexpectedly good electrical production. So why believe the Spirit story unreservedly, when the people telling that story seem unable to account for the condition of their other Rover?
This problem is currently open to consideration and we should consider it .. carefully.

At present, the dust story is inconsistent.
Question it!
That's how discoveries are made.

djellison · 2004-12-21 05:17:14

You dont need a doctorate to tell you that you can tell NOTHING from a single greyscale raw JPG's that get put on the JPL website either. You at least need to go to the trouble of making a colour image - and then - at least - compare it to Opportunity

If that doesnt demonstrate that Spirit IS dustier than Opportunity then what does. It also demonstrates a possible cleaning action involving a dust devil or similar event crossing over Opportunity - picking up dust from the open flat array area, and dropping it at an area of low wind speed around where there would be turbulance because of the Pancam hold-down bracket.

The simplest answer is often the right one - and a perfectly simple and understandable answer is looking right at you in that picture.

You made the assumption that this patch of Spirit was 'essentially dust free'

Oops?

Doug

Shaun Barrett · 2004-12-21 06:16:53

Interesting. Thanks, Doug.
These are much better pictures than I've been looking at and the detail is far clearer in colour. Nevertheless, while the actual solar panel segments on Spirit appear paler than those on Opportunity, so does everything else - even though the detail on Spirit is just as vivid, perhaps even more vivid.
I still don't see convincing evidence that Spirit is carrying significantly more dust than Opportunity.

Could the Spirit pictures be more exposed than those of Opportunity? Or could the Opportunity pictures have been taken through a filter?

I'm not going out of my way to be a pain-in-the-posterior here. I'm genuinely trying to see more dust on Spirit than Opportunity but the clarity of the detail on Spirit honestly leads me to think otherwise. Even the (upside-down) printed part number, 10207341-1, is at least as readable on Spirit as it is on Opportunity - if not more so.

As for the dust-devil idea, I remain totally unconvinced by it. At one stage, NASA was claiming that dust-devils must have blown straight over Opportunity on three separate occasions to explain the surges in electrical power in recent months. Yet, no evidence of dust-devils has been apparent in the hundreds of photos taken by either MER. And who's to say a dust-devil wouldn't deposit more dust on a MER's solar panels than it removes anyway?
I've lived in a desert climate long enough to know that, when I wash my car in that kind of environment, a strong 'willy-willy' (Australian for dust-devil) means I'm going to have to wash the car again! And I've never ever seen a willy-willy clean the dust OFF anybody's car!!

But then, you and NASA are probably perfectly correct. God knows, you've got more brain power on your side than I have on mine!
But I still haven't seen enough evidence from your side to convince me.

djellison · 2004-12-21 07:01:13

The first image is the most obvious one. If it were an exposure issue - then the Spirit solar arrays would perhaps be grey, instead of near-black - but they're not - they're very very very brown - other dark areas are less dark than they appear on Opportunity

Compare the colours of components such as the silver bracket the pyro-device for the PMA tie down was situated - it's very much the same shade in both images.

The RGB values of similar components in the two images are very much the same - the blueish clamp, the goldish bolts, etc etc. I'd suggest that these pairs of images are very comparable - and any differences are at least 75% real, and not artifacts of exposure or processing - of that I'm highly confident.

The 'events' Opportunity had were all overnight - so perhaps it is some nocturnal, or perhaps a dawn or dusk event, a time when the rovers are fast asleep - that causes whatever it is that made this happen. Maybe not dust devils per se - but a dawn breeze whipping over some rocks at a strange angle. Remember - Pathfinder took 17,000 odd images in less than 90 sols and caught a dust devil in three of them taken seconds apart. Thus - given an average of 188 images/sol you should see one dust devil every 90 sols given Pathfinders conditions. Bearing in mind huge numbers of images at MEr are of the sun, dust opacity observations, MI, or of the ground itself - with an average of approx 92 images/sol for Spirit and 90 images per sol for Opportunity - many of which couldnt have ever seen dust devils - its little suprise that neither rover has seen one.

If you dont see dust - you dont see dust - but it looks totally and utterly obvious to me that Spirit is much MUCH dustier than Opportunity - and, given the reduced power, and no other reason why such a power degredation might occur - it seems very very obvious.

Solar arrays with dust on would be lighter than those without. They're very nearly black when new - and martian dust is a butterscotch colour. To compare the solar array colour in those images is folly - as that's what we're expecting to see a difference in. Compare other features, bolts, clamps, etc etc. If things were covered in dust - they WOULD appear lighter

I'm sure you're not trying to be just awkward- but really - when I see dust as being so chronically obvious in those images - and yet you say it isnt - then what more can I say

Shaun Barrett · 2004-12-21 08:04:45

Thanks again, Doug.
You may or may not know I'm mildly colour-blind. I can see most colours O.K. but some shades of green and brown throw me. With this in mind, I gave some thought to what you said about the solar arrays on Spirit:-

The first image is the most obvious one. If it were an exposure issue - then the Spirit solar arrays would perhaps be grey, instead of near-black - but they're not - they're very very very brown - other dark areas are less dark than they appear on Opportunity

They didn't look brown to me (but what do I know?), so I called my colour-normal wife in to have a look at them. I asked her to look at the panels on Spirit in the first image and, without reference to anything else, to tell me what colour they appeared to her. She said: "Grey."
I then asked her if she was sure they weren't some shade of brown. She said they just looked "pale grey".
I have to admit, I was relieved to hear that she agreed with me on that because I don't like being colour-challenged and hate it when everyone around me, including my wife, sees an object as a different colour. It's still disconcerting even after all these years!

Another thing about the pictures is the surface adjacent to the golden washers or flanges. It has a criss-cross hatching pattern on it, which reminds me of an old design of laminex for table-tops and benches.
This pattern, as well as the part number nearby, is perfectly clear on Spirit; probably even more distinct than the same surface on Opportunity. Even the large circular object's fine linear pattern is more obvious on Spirit than on Opportunity.

I know this must be exasperating for you, Doug, but it still looks to me like these pictures were taken under different conditions - almost like one was taken through a polarising filter or something like that.
The dust explanation doesn't seem to fit properly, at least to me.

In any event, I still can't see how dust-devils are going to clean the dust off anything, even assuming they do all sneak up on Opportunity when it's not looking but never go anywhere near Spirit.

Don't despair, Doug. You've done your best.
I guess it's just me!

Palomar · 2004-12-21 08:11:55

*The way things are going -- and have gone, for all these months -- I really doubt we're going to get images of dust devils upclose. If it hasn't happened by now... Yes, the missions have been spectacular successes and I'm not trying to negate that in any way.

I was hoping for some pics (at least 1!) of a dust devil within the near vicinity of either MER...but considering their ages and all, well...

Maybe Mother Nature and luck will prove me wrong. I hope so.

--Cindy

djellison · 2004-12-21 16:40:17

Statistically, the chance of getting a dust devil on camera is TINY.

MPF took 16,500 images in less than 90 sols. WHAT - THAT MANY - fear not - they were each 1/16th the res of MER - but covered a similer field of view.

So - averaging 183 IMP images per sol over 90 sols - they caught a dust devil once - in three succesive images.

Now - of the 61,000 odd MER images - I'd estimate 75% to be Pancam - so that's say 46,000 images - in a total of 668 sols of surface operations - only 68 images per sol with pancam - perhaps 20 images per sol with Navcam. Statistically, we've always been less likely to spot a dust devil.

Doug

Stephen · 2004-12-22 00:24:29

Statistically, the chance of getting a dust devil on camera is TINY.
MPF took 16,500 images in less than 90 sols. WHAT - THAT MANY - fear not - they were each 1/16th the res of MER - but covered a similer field of view.
So - averaging 183 IMP images per sol over 90 sols - they caught a dust devil once - in three succesive images.

I note that the camera Michael Malin will be building for MSL will be able to do 10 fps video (& do it independently of the rover's own computer). It seems to me that capability would not have been included unless he (or somebody) had dust devils in mind.

(I also note the MSL will also be carrying a meteorological package. With hindsight, such a package should have been included in the MERs' Athena science pack. At least then there might have been a chance of gathering data on these mystery cleaning events.)

djellison · 2004-12-22 04:58:43

Athena was never designed to do Met work. The volume, mass, power and data budget preclude it being included anyway. Spot measurements are possible with Mini TES however

Doug

Palomar · 2004-12-22 09:44:46

You dont need a doctorate to tell you that you can tell NOTHING from a single greyscale raw JPG's that get put on the JPL website either. You at least need to go to the trouble of making a colour image - and then - at least - compare it to Opportunity
...If that doesnt demonstrate that Spirit IS dustier than Opportunity then what does.

*I dunno Doug. They look amazingly similar to me. All images look nearly exactly like "twin" images (of course the MERs -are- twins) and the pics of Oppy (color or grayscale raw) are much darker than the pics of Spirit.

Maybe I need to visit my optometrist again soon, but you haven't proven your case to me. Again, these look like the same photos (with some *very minor* differences and nothing to do with looks like dust), except one set is darker than the other.

--Cindy

djellison · 2004-12-22 12:39:37

Can you guys really not see how the dust is clumped up into small areas on Opportunity - particularly around the PMA hold down bracket? I'm not seing things here - this is real stuff I'm talking about. I'm not trying to be stubourn or stupid - and I had my eyes tested only a few weeks ago so I know I'm not seing things. What has happene here couldnt be more obvious. Brutal, obvious, unmistakeable difference in colour between the two rovers - and a difference that corresponds very very well to a dustier surface on spirit, and a 'cleaned' surface on Opportunity. I

Honestly - guys - cant you see it? This isnt some "oo - a rock that looks like a tank" type thing - this is verbose, obvious colour differences between two identical objects in similar lighting conditions.

I'm trying to be as scientific as I can here - but I see no need to be honest - the images tell the story so very very loudly!!

http://mer.rlproject.com/dust_move_waaa … waaaaa.jpg

Look at the are below the text - it's roughtly one average colour throughout - whereas with the opportunity image, there is a darker area, and some browner clumpy areas. Can you not see how one can become the other? Cant you see it?

I've brightened the Opportuity image a LOT - it's without doubt brighter than the spirit image - but look at the solar cells

Bluring it to eliminate noise - an Opportunity cell comes in at an RGB value of 73:103:77

Same process with Spirit produces 104:109:82.

If we take an average of all 6 values to make a grey value - it's 91

Surely you can see that the NEITHER are grey - and one is considerably more 'tan' than the other?

Doug

atomoid · 2004-12-22 18:12:23

Spirit looks a bit dustier than Opp, based on all the pictures ive seen, especially Doug's.

Even if this were only an illusion due to exposure differences based on atmospheric effects causing the Spirit picures to be less contrasty and appear more washed out (and its understandable that its hard to get an 'objective' reference for contrast for these images anyway), then it will still beg the question of why:

Another consideration is that if Gusev has more atmospheric scattering to cause this effect in the first place, then it would be due to having more dust in the air, and since theres more dust in the air, then its also likely to be falling on the solar panels and building up at a greater rate. When you look at Meridiani soils, theres not much dust to be had, at least relative to all the red drifty dust everywhere in Spirits photos, so unless its blowing in from afar, and i tend to think most dust on the Rovers is of a somewhat local source, at least in recent terms (as its all blowing everywhere around the planet in the long term picture), that would explain why Meridiani with its desert pavement of Spherule berries is keeping the dust from lifting from under the surface, so only a little local-source dust is blowing around leading to a much lower concentration in the lower atmosphere at least (do we have good measurements of atmospheric averages in both places?). The pictures appear to demostraqte this pretty well.

Palomar · 2004-12-22 19:29:01

Surely you can see that the NEITHER are grey - and one is considerably more 'tan' than the other

*The uppermost one is close to hunter green in color, the middle one is more olive in color, and the last one is dark liver-colored. But yes, I think I see what you are getting at.

This isnt some "oo - a rock that looks like a tank" type thing -

*Hey! That rock looks like a tank! [Erm...hahahaha...just kidding. ]

--Cindy

djellison · 2004-12-23 03:02:19

Spirit looks a bit dustier than Opp, based on all the pictures ive seen, especially Doug's.

VICTORY

You've just made a silly young man very happy on his Birthday

Doug

GraemeSkinner · 2004-12-23 04:31:32

Spirit looks a bit dustier than Opp, based on all the pictures ive seen, especially Doug's.
VICTORY
You've just made a silly young man very happy on his Birthday

Happy birthday Doug :band:

Spirit does look dustier on the link you provided, but opportunity has a different wiring layout - I thought they were supposed to be the same.

Graeme

Shaun Barrett · 2004-12-23 18:41:19

Yes indeed, Doug.
A very Happy Birthday to you.

Well, now I've not only got Doug, NASA, and Atomoid telling me Spirit's obviously dustier than Opportunity, but Graeme's joined the fray as well!!
I'm starting to feel inadequate here! :laugh:

I still can't convince myself that the difference in appearance isn't largely to do with different lighting or filters or some other treatment of the images. I'm just looking for evidence of physical obscuration of detail by a layer of dust - and I'm not finding much consistent visual evidence for that.

But I have to face reality here and admit I'm up against a few factors which weigh against my position on this:-
1) Spirit's power is down compared to Opportunity's.
2) Spirit is travelling in dustier surrounds than Oppy's sandier
environment, so you might expect more dust.
3) It's certainly possible to interpret the pictures Doug has
presented as showing more dust on Spirit's panels (though
I personally find the evidence inconsistent).
4) NASA and a majority of people engaged in this debate are
convinced dust is the explanation.
5) I have no plausible alternative explanation.

Another thing is that I don't know how much dust I'm looking for. The amount of dust required to reduce Spirit's power output by so many hundred units is not clear to me - maybe I'm looking for more dust than is necessary to cause the reduction. I don't know.

Since I'm unable to come up with anything useful to add in my own defence, and faced with overwhelming odds, I'll have to withdraw from the debate - still unable to explain the situation satisfactorily in my own mind. But I do appreciate all the feedback I've had, especially from Doug who's gone to a lot of trouble to elucidate the discussion. (Thanks again, Doug.)

In any case, this all started with me suggesting dust may not be such a major problem for future Mars expeditions, after all. That was the main point I was trying to make in my post.
The fact that it's even possible for someone awkward, like myself (! ), to argue they can't see a great deal of evidence of dust on solar panels exposed for nearly a terrestrial year to martian conditions, is enough to bolster that suggestion in my view.
Dust or no dust, my bag is packed and I'm ready for NASA's phone call!

GraemeSkinner · 2004-12-23 21:53:05

I still can't convince myself that the difference in appearance isn't largely to do with different lighting or filters or some other treatment of the images. I'm just looking for evidence of physical obscuration of detail by a layer of dust - and I'm not finding much consistent visual evidence for that.

The area of the image that convined me was lower right. Surely NASA can tell from its data if they are receiving less power from the solar cells on Spirit.

Graeme

rgcarnes · 2004-12-24 00:27:15

There is a difference between the images given of Opportunity's and Spirit's solar cells. The problem is that the lighting is slightly different, so that a judgement of performance on the basis of these two images is difficult to make.

Judging by the shadows, and the brightness of the metallic pads, both at the base of the screw and the solder tabs in the lower mid right, the Spirit image is taken at a viewpoint just barely out of line with a specular glint of the sun from the cell surfaces. At this position, we probably are observing cell surface brightness due to scattering, as such a sun angle provides a most sensitive view of scattering from small defects or dust particles.

The fact that the metal pad and tabs are so much brighter in the Spirit image than in the Opportunity image indicates that we are not in as good a position to observe possible scattering centers on the Opportunity solar cells with nearly the same degree of sensitivity.

If I were going to really make an assuredly valid comparison of the two unit's solar collection surfaces, I'd want an image from the start of the mission for each unit's solar collection surfaces taken under the exact same sun angle to compare with the 300-plus-day images we now have. This is probably an unrealistic want, especially after the fact.

I'd also want to know if the solar cells from both rovers were from the same production run. On a material with such a high index of refraction as silicon, functional antireflection coatings can have somewhat differing colors in reflection and yet still be effective at their job, and pass their specification criteria.

Shaun, I share your color vision type. It should be pointed out that the formal descriptions of color vision are derived from surveys and tests on many people to determine what proper color vision is. It's essentially majority rules and all that. In my studies into the subject I've found hints that those with our type of color vision are more sensitive at low light levels than those with "standard" color vision; something with a slight survival advantage in certain situations.

Finally, to cover the "dust devil" topic, reiterating from past posts, I don't believe that the size, energy, and persistance of the rotating cyclones on Mars could be supported by heated dry atmosphere and dust. I believe they are powered by phase changes of water from a very near surface vapor layer rising and freezing to fine solid particles. Such particles could, by the way, scour a solar cell surface clean.

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Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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#18 2004-12-22 12:39:37

Re: MER search for dust devils - hoping for a rover's eye view...

#19 2004-12-22 18:12:23

Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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Re: MER search for dust devils - hoping for a rover's eye view...

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#24 2004-12-23 21:53:05

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Re: MER search for dust devils - hoping for a rover's eye view...

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