Martian Ice (APOD 02 Jun 2008)

[Bad Buoys]

So if that is ice under Phoenix, why is it at different levels? Though the 'ice' exposures by the far leg all seem about the same height, the exposure closest to the camera seems much higher. Isn't the surface temperature fairly uniform such that all ice would be at the same depth?

Or is this just heavy frost which was blasted by Pheonix into a concrete looking surface and can happen at different levels, especially if Phoenix was blasting one jet heavier to maintain vertical axis integrity?

[Qev]

I think the height difference could be a simple illusion due to the field of view of the camera, and the difference in light levels. Then again, permafrost slabs don't necessarily all lay at the exact same depth.

[flamencoprof]

The shadows of the legs look as though its steeper and further down to the right, my bet is different levels, tops of smaller-scale frost heaves?

[jeepien]

I think the word is "braking" rocket. (Or did something break on the way down?)

[orin stepanek]

http://apod.nasa.gov/apod/ap080602.html

If it is indeed ice, than the backhoe won't have to dig very deep.
Orin

[Sputnick]

Are we all aware that on earth bacteria thrive in the layer where glaciers meet rock? I believe it is impossible for life to be anything but abundant on Mars.

[Animation]

I didnt notice any ice in the pics away from the craft. What are the odds there would just be ice under the craft? Maybe some condensation or something from the lander's entry ended up running off and collecting underneath, forming ice?

Or maybe its a trick of the light?

I guess they'll figure it out soon.

Lewis

[iamlucky13]

It seems most likely that this is permafrost that was exposed by the thrusters blasting loose sand away during landing. The loose sand covering is not necessarily uniform in depth (we know there's ripples in the soil, we see it in the polygons), nor is the soil necessarily all exactly the same temperature. The polygons, rocks, etc, all would affect heat transfer through the soil during the seasonal melt, so the permafrost layer would likely ripple as well, rather than be perfectly flat.

[ta152h0]

does ice turn to vapor without liquefying first on MARS ? unlike beer here on Earth ?
Pass the beer

[henk21cm]

I think the height difference could be a simple illusion due to the field of view of the camera, and the difference in light levels.

I agree with you. It is not easy to describe, i'll try. The downloaded image is 792 by 396 pixels. At the edge of the white patch at pixel (466, 228) a narrow shadow is visible, being an indication that there is just a slight difference in height between the darker and lighter material. A similar shadow is at (710, 212). For a deep pit the shadow should have been longer. The lander is at 68 degrees north, and it is just spring time.

At the top of the image three trusters are visible: (320, 10), (560, 10) and (690,10). These may have blown the dust away from the ground, directly beneath the lander.

Horizontally through the image at y=300 runs a seemingly coarsely grained elevation. When zooming in, the grains are artefacts of the DCT compression algorithm. In front of this 'ridge' (400, 175) lies what seems to be a bulge. However when you turn the image upside down, the bulge looks like a pit. So our brains interpret the image, being misled by our eyes and brain.

Now the white patches. The image is not fully saturated. When picking random pixels in the left white patch (380, 245), the brightness is 218 (of 255). Repeating this operation with the right white patch, (650, 245) the brightness is 225, slightly more white. Looking at the shadow of the foot (382, 168), the sun shines from the right. The right white patch lies more in the direction of the sun and is therefore a little lighter. Note that the struts are oblique and cannot serve as a needle of a sundial. Again look at the right white patch. There is still 'dirt' on it. When looking in more detail to the left white patch, one can see some grains, pebbles, specially in the shadow of the strut.

Look at the material around the foot. In a wide area texture and brightness of the image is of comparable composition. Suppose the white patch is the top of bed rock. The lander would not penetrate this bed rock, so it would come to a halt when it touches the sheet. That would give you information about the thickness of the dusty top soil.

Finally compare the brightness of the rock at (251,85) with the brightness of the white patches. The rock ranges between 230 and 240, even whither than the white patch. The white patches look very white and bright since there are shadows to compared with. The differences enhance the range between dark an light. It is a trick of our brain.

Frozen soil looks similar to not frozen soil. There is not much difference between the two. It does not color white. If its is white, the reason is condensation of water vapour on the very cold soil, like frozen fog.

My conclusion -and hypothesis- is that the white patches are rock, exposed to the sunlight in a dusty environment. Yes, i know, this conclusion may be completely wrong.

What tickles the imagination are the barnacle shaped protruding objects on the leftmost struct (124, 90). What are those? Lumps of frozen propellant?

[Sputnick]

Henk .. can you give a similar description to TA as to why in the hands of an avid earthman beer can never evaporate?

[apodman]

Animation wrote:

What are the odds there would just be ice under the craft?

If I aim for a bull's eye, I am more likely to hit somewhere else nearby than right in the bull's eye simply because the nearby area is much larger than the bull's eye itself. Yet when I compare the likelihood of hitting the bull's eye to the likelihood of hitting any other equal area nearby, I am more likely to hit the bull's eye simply because it is in the center of my aiming area.

Probabilistic gibberish, perhaps, but it says to me that I shouldn't be surprised if I actually hit what I'm aiming at. Of course I'm talking about hitting an area in the target example and hitting a result in the case of Mars, but if you shoot for ice you might find it.[/quote]

[iampete]

. . . My conclusion -and hypothesis- is that the white patches are rock, exposed to the sunlight in a dusty environment. Yes, i know, this conclusion may be completely wrong. . .

Something to consider that might lend support to your hypothesis:

The decomposition of hydrazine is highly exothermic (per Wikipedia, combustion chamber temperatures hit ~800 C) and produces large volumes of hot gas. Would it not be reasonable to expect that exposure to the plumes even of a second or less (assuming the plumes are at least a meter or two in length just prior to touchdown) would have created some visible deformation/sculpting/whatever to the patches if they were in fact ice? (EDIT: the picture in Bad Buoy's post on the following page exhibits some of the deformation/sculpting/whatever I would expect from an ice chunk exposed to a thruster plume for a short period.)

. . .What tickles the imagination are the barnacle shaped protruding objects on the leftmost struct (124, 90). What are those? Lumps of frozen propellant?

My gut feel is that that is unlikely. Thruster shutdown likely takes on the order of tens, possibly a few hundred, of milliseconds and the amount of non-decomposed hydrazine is probably miniscule as the thruster temperature still remains high.

It is more likely to be soil that was displaced by either the plumes and/or the shock of actual landing that, in falling back down, happened to stick to the structure. As to why more stuck on that leg than the others, I don't know, but it may have something to do with the fact that it is in the shade and doesn't experience the same thermal influences as the others, which had their collection fall off.

[apodman]

P.S. If somebody can tell me how to insert a quote or image without hacking it up like I just did, I'd appreciate it. I apparently don't understand the proper use of the formatting tools in the text editor.

[apodman]

And another apology. Animation wrote "would just be ice under the craft" and I read and repied to "would be ice under the craft", leaving out the meaning added by the critical word "just". Again, sorry. I'm going to stay away from the keyboard until a degree of competence returns.

[astrolabe]

Hello iamlucky13,

I'm inclined to agree with you on this one; it appears to me that the landing pads are sitting on small berms. Another thing is the area around the far pad looks relatively free of stones that are seen farther out. The rocks may in fact be there but were covered by sand blown aside by the thrusters.

[ta152h0]

maybe they can jump the beast by firing the thrusters and move to another location, a la Surveyor ?

[Qev]

does ice turn to vapor without liquefying first on MARS ? unlike beer here on Earth ?
Pass the beer

For the most part, yes. Liquid water can exist on the surface of Mars in a very narrow temperature range, but sublimation would certainly be much more common.

[Bad Buoys]

Apodman: there are examples to follow as you mouse-over each command [and they only appear when posting]

But there are a couple more interesting items about the APOD image. Firstly it seems to be too jpg degraded [note the worms frothing the soil in shadow] for too detailed an analysis.

But someone mentioned the scales on the nearest pad strut. And that does appear interesting as I don't see anything similar on other horizontal surfaces.

And there seems to have been slight horizontal movement of the craft at touchdown. In the far blast exposure there seems to be a very small amount of soil disturbed by the pad and rolling down ending atop all else. So the engines must have been shut down just prior to touchdown.

And while two thrusters appear flared, the nearest seems to be in some degree of focus.

JPL has other images most of which are dealing with the before and afters of Pheonix's first scoop whose contents are also shown.

But there is another ice(?) structure under Pheonix which they've named "Snow Queen". This time I'll try to link the image to the JPL page. See if it works and click on the Snow Queen picture below.

[Bad Buoys]

Apodman: I also notice you'll see the exact coding which must be typed for my last by clicking on "Quote". That and the mouse-over examples should give you the programming.

[Sputnick]

The chances of the craft landing atop ice would be, I estimate, 100% .. because it is close the North Pole and the pole's icecover .. and according to what I consider the best educated guesses based on spectral analysis etc. there are continent-large areas of ice not far beneath the topmost, thin layer of soil even at the equator. I think it more than likely that Mars had continents and oceans, and the oceans evaporated into space only to an extent, before freezing. Then the big volcano blew dust all the over the planet, thinly covering the ice. However, yes, I would have expected ice to have been more deformed by the thrusters, except perhaps considering the sandy soil would be a tremendous insulator, and only the lander's operators know how long the thrusters operated at intimate distances. Does anyone know anyone to ask to determine how long the thrusters would operate between the point the first hot gas touched the surface, and touch down and shut off? perhaps the thrusters shut off even before touchdown, and that would disturb the environmentas little as possible before experiments began. I have to admit I'm so clever to think of these things .. I sure wish I was educated.

[Sputnick]

I had not seen the photos of what looks like thruster-dug pigs before posting .. but if they were thruster dug wouldn't the caption have included that information? In any case .. hey .. does anyone want to form a partnership for Martian ice mining .. how about $100,000 per ice cube to cool a Billionaire's vodka?

Another factor in all this which has been mentioned in the forum is that ice will melt at different temperatures according to composition. A World War Two effort involved building transport ships out of ice using water mixed with sawdust. I think the sawdust ice melted 10 times slower.

[henk21cm]

The decomposition of hydrazine is highly exothermic (per Wikipedia, combustion chamber temperatures hit ~800 C) and produces large volumes of hot gas. Would it not be reasonable to expect that exposure to the plumes even of a second or less (assuming the plumes are at least a meter or two in length just prior to touchdown) would have created some visible deformation/sculpting/whatever to the patches if they were in fact ice?

Pete, that is quite possible. You write the exhaust gasses are hot (1000K in the combustion chamber) and they have a large volume. I have to estimate the volume and its pressure. Well, estimate, it is rather a wild guess. Suppose 1 m³ of hot gas at 100 kPa pressure comes free during the last few seconds. Since the temperature is high, the mass of the exhaust is smaller than at 273K. Roughly four times smaller: 0.25 kg.

Specific heat of ice at 200 K is 1.5kJ/kg/K
Specific heat of nitrogen gas at 500 K is 1 kJ/kg/K.
Melting heat of ice: 240 kJ/kg

So solve the equation:

Cooling the hot gas - heating up and melting ice = 0, or:

0.25 * 1 * (1000-273) + x * ( 1.5 * (150-273) - 240) = 0. This leads to:

x = 0.25 * 737 / (240 + 185) = 0.45 kg

(mass * specific heat * temperature difference = heat)

Half a liter of water! Feasible, when one looks at the size of the holes in the soil.



It is better to flip the image upside down, it looks a bit more logical. My impression of the size of the holes: roughly 0.1m wide and 0.1m deep. However, there is no reference other than some pebbles near the hole.

Concluding: the amount of ice to melt is of an order of magnitude comparable to the potential size of the holes. It is neither 1000 larger nor 1000 times smaller. So melting can not be excluded, however it is not proven that the melting hypothesis is true. We need more accurate volumes and pressures of the exhaust gasses. Thats an item to be dealt with by NASA's rocket scientists.

About the 'barnacles':

My gut feel is that that is unlikely. Thruster shutdown likely takes on the order of tens, possibly a few hundred, of milliseconds and the amount of non-decomposed hydrazine is probably miniscule as the thruster temperature still remains high.

It is more likely to be soil that was displaced by either the plumes and/or the shock of actual landing that, in falling back down, happened to stick to the structure.

You are right about the trusters. Shut those down immediatedly, if you want an undisturbed site! But why does this dust stick to the tubes? A rounded pebble lying on a round tube is in a very unstable position. To put this to the test, tilt a broomstick to the wall an drop randomly some pebbles on the broomstick. Do they stick on the broomstick? You may try a meter of rain drain pipe as well.

Moreover there are some protruding objects at the side of the tube. Those should have been falling down. These object can not be seen on the other legs, most likely due to the limited resolution of the jpg and its lossy compression. I hope to stumble over a lossless image, like TIFF or png. Maybe something for an APOD in the near future?

Note: I had to edit this message due to a silly error. Where i had heat capacity written, it should have been specific heat. That has been corrected now.

[iampete]

. . . But why does this dust stick to the tubes? A rounded pebble lying on a round tube is in a very unstable position. To put this to the test, tilt a broomstick to the wall an drop randomly some pebbles on the broomstick. Do they stick on the broomstick? You may try a meter of rain drain pipe as well.

Moreover there are some protruding objects at the side of the tube. Those should have been falling down. . .

Actually, I was thinking more along the lines of clumps of dust/dirt, rather than pebbles.

Your analysis of the potential for melting of ice leads me to consider another mechanism: is it credible to think that in the final few deciseconds prior to thruster shutdown, there exists a swirl of dust/soil particles and melted water droplets under the lander? When the thrusters shut down and things start to settle, some of the water droplets mixed with the dust settle on the leg surfaces as well. In the absence of heat from the thruster plumes, the water (mixed with the dust) would re-freeze and "stick" on the structure. This re-freezing would not be extremely quick, since even after thruster shutdown, the radiative heat from the thrusters themselves would take some time to dissipate.

[apodman]

This is only a test. Thanks B.B. Sorry everyone for using this actual forum for training.