Planet Four Talk

Patchwork feature

  • jules by jules

    I'm used to the Moon so don't have a clue what this could be! Sand dunes? Think I need to go and read up about Mars!

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  • mschwamb by mschwamb scientist, translator

    These are channels carved into the dirt underneath the CO2 polar ice cap on the south pole of Mars. The channels are carved by CO2 gas that forms underneath at the base of the ice sheet as the base of the CO2 ice sublimated by the Sun . These channels can have many forms so we call them an araneiform . Some look more like "spiders" where you have many channels radiating from a single point,
    Cheers,
    ~Meg

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  • jules by jules

    Thanks Meg - things are slowly beginning to make sense.

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  • michaelaye by michaelaye scientist

    Actually, in these cases where the patchwork looks so patchy, we believe that the fans erupt from cracks in the CO2 ice layer without necessarily having carved channels underneath yet. We tested that by looking in separate years and they do not repeat at the same exact positions. Fans from 'spider' arms are quite reliably repeating between the years.

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  • danmizzou85 by danmizzou85

    This is a really neat picture. I was going ask what the scale in kilometers/miles is for these photos, thank you.

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  • Portyankina by Portyankina scientist

    distance between parallel cracks is usually about 200m

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  • danmizzou85 by danmizzou85 in response to Portyankina's comment.

    Hey, very interesting, thanks for letting me know. I think is very fascinating like everyone else to be involved with helping you guys on this project. One last question I had was if there is any way to know where on the planet these pictures are taken of, or if we should just ask you guys directly if we find an interesting photo. Thanks again, awesome stuff! Keep up the great work!

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  • Portyankina by Portyankina scientist

    Hi again!

    I can tell you that it is southern polar areas, about 80 deg latitude. But I myself do not know the actual location of this image, we want to keep the test "blind" so that people do not prefer some areas to others. The data of course stored in the data base, but I'll know about it only after most job is done.

    And thank you for your help with this! I am really-really happy people enjoy this project!

    Anya

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  • john_cooper_35hotmail.com by john_cooper_35hotmail.com

    Could these be bed's of under surface Co2 ice that when sublimates creates a Air Hockey type of situation?

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  • watsonglv by watsonglv

    These areas look very similar to convection cells which commonly occur in earth science and give rise to thermal plumes. The effect is easy to demonstrate (using Lyle's Golden Syrup and a sub-suface heat source) Such structures naturally trend to hexagonal forms which can vary in size with the viscosity of the medium: sand or dust would be ideal media. Such an explanation begs the question as to how the thermal source arises at a sub-surface level as opposed to surface heating from the sun; the explanation may involve the contrasting thermal conductivity of rocks and gases present. It would seem that thermal pressure is releived by a venting of gases which correspondingly tends to be central to the hexagonal form.

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  • watsonglv by watsonglv

    Having had further thoughts about the practicalities of the 'convection cells' idea I was wondering about the viscosity of the sand/dust and how the mobility of the particles might develop. I liked John Coopers notion of 'air hockey' type effects and extended the idea to a possible state of liquifaction arising as the start point of the convection cell. As the CO2, or other gases, is mobilised with increasing temperature at the surface, a state of liquifaction reduces the viscosity of the sand and dust to a point at which a natural convection cycle begins, eventually allowing the semi-hexagonal structure to form. The interaction of nearby cells distorts the 'ideal' hexagonal forms to those we see in the pictures. Eventually the gases force their way to the surface at the most mobile point in the convection cell, the midpoint, hence the central plume.

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  • MNottingham by MNottingham

    I've only just had the chance to watch the show and was fascinated by these quilt like formations. The patterning looks quite similar to a process found in permafrost on earth: I've heard it called several different things but the most common is 'ice wedge polygons' I believe. Could a similar process be happening here?

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  • gepisar by gepisar

    This reminds me of Chocolate Hills, Cebu, Philippines. From the air (on google earth) the structures look similar. (See aerial photo on wikipedia: http://en.wikipedia.org/wiki/File:Chocolate_Hills_Bohol.JPG) These are 50m is size, which seem comparable.

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  • michaelaye by michaelaye scientist in response to watsonglv's comment.

    We currently believe that a better model for the sub-ice-surface heating is what's called a solid-state green house effect: The ice layer is translucent enough for the sun to penetrate into the ice, but, like in the Earth's atmosphere, reaction with the media changes the wavelength to the longer side, rendering the light unable to escape, hence, over time, a warming up of the sub-ice surface.

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  • michaelaye by michaelaye scientist in response to watsonglv's comment.

    you seem to ignore that the sub-ice sublimation happens against the rising pressure, induced by the all-present co2 ice layer on top of the newly created co2 gas. There is just not much room for convection to happen on meter-scale. sure, on centimeters one can't avoid it, but we are quite sure that convection is not the explanation for these visible cells. More likely, we currently think, is the general pattern of crystal breaking, that happens in a semi-chaotic fashion, also here on Earth. It is very hard to predict the splitting lines of solid crystals, and as the conditions on Mars' surface favor a very clean and solid CO2 ice layer that had the whole long 6 months winter to solidify, we think it would be natural to show similar breaking characteristics to crystals, maybe even becoming amorphic in characteristic, like glass. Compare with this image: http://www.giantbomb.com/breakable-glass/92-3138/all-images/52-324210/break_glass/51-1276469/

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  • Wounded_Knee by Wounded_Knee

    found an image that could be the network before it blows, the fine cracks cover the dark material lines.

    http://talk.planetfour.org/#/subjects/APF0000hen

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  • Wounded_Knee by Wounded_Knee

    forgot to mention that in my description of this I quoted mounds when they are depressions (was very tired)

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  • gepisar by gepisar

    The white patches look like the twinkling one sees when looking down on the ocean on a sunny day.

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  • ianbutton1 by ianbutton1

    I go with the optical-illusion theory. Surely a flat rippled dune surface, with fans of black dust perpendicular to the ripples, drifted down from plumes emanating from linear cracks. You can see some dunes cross the cracks - sand wouldn't behave like that on a deeply incised surface. Are any of the plumes active - at certain times do they cast fan-like shadows on the surface, at a different angle from the fans themselves? In these photos, the sun seems to be exactly behind the plumes.

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  • michaelaye by michaelaye scientist

    I'm not sure, how you make out that the sun would be behind the plumes, but I can tell you that the sun comes from the lower right (a bit more right than low.) See here: http://uahirise.org/ESP_012081_0930

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  • Wounded_Knee by Wounded_Knee

    if the sun is lower right then the bright spots are depressions

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  • Wounded_Knee by Wounded_Knee

    just had a thought, could the bright depression act like a parobolic mirror and focus the light and heat to the opposite wall, thus leading to oval depressions?

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  • Wounded_Knee by Wounded_Knee

    I`am looking hard, are you sure the Sun from the lower right?. it has upper left written all over it 😃

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  • Wounded_Knee by Wounded_Knee

    sun lower right, middle section has a few mounds that give the upper left impression

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  • Wounded_Knee by Wounded_Knee

    if the suns heat passes through the clear ice and strikes the bright wall, then gets trapped by the greenhouse effect, could the minute convention cells over years lead to the perpendicular channels that emanate from them

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  • Wounded_Knee by Wounded_Knee

    if so it would explain the nature of the channel spreading north/south, and the veins spreading east/west.....(thats if north is up in all images)....?

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  • Gez_Quiruga by Gez_Quiruga

    This reminds me of a bouncy castle being inflated. Could there be more gas than solid within?

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  • MoonSquirrel by MoonSquirrel

    It looks similar to this image APF0000mvz with similar vent patterns, only real difference is the colour. Could the red be caused by the sun? Maybe dust in the atmosphere?

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  • wassock by wassock moderator

    According the star gazing live these features move. does that mean they are in a different, random, place each year our do the shapes themselves move over the surface?

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  • jellyhead by jellyhead in response to michaelaye's comment.

    So they are not actually channels in this picture, just the debris left behind from the melted ice sheet? Is relief the key factor here? So where you have the spider features radiating from a single point, that point is the highest point and something about the movement of the ice/gas downhill causes permanent channels. These permanent channels then dictate the crack propagation through the ice sheet resulting in the same features each year. Where the area is flat, then the natural breakup of the ice sheet allows the gas and the debris through so when it melts you are left with a pattern which shows you how the ice broke up - this would be different each year.

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  • wassock by wassock moderator

    is this an image where there is a covering of ice or is this a summer image? I if there is no ice cover and we're seeing the red surface, excepting maybe the 'boulders' , then could this just be what it looks like when one of the cracked surfaces melts and drops the dust thats been on top of it? So we have a flatish surface given apparent texture by some dirt shading?

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  • Rockykrys by Rockykrys in response to wassock's comment.

    I have a similar question: Does this image show sand/dust layer deposited over an ice sheet that is still there, or has the ice melted leaving behind the surface features that were previously created on top of the ice?

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  • Rockykrys by Rockykrys in response to mschwamb's comment.

    Hi, I thought this image showed a sand/dust layer deposited over an ice sheet that is still there. Are you suggesting that the ice has already melted leaving behind these surface features, which were previously created on top of the ice?

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  • Wounded_Knee by Wounded_Knee

    If you look at these images in order you can see the before middle and after of the process???

    APF0000hen
    APF0000i00
    DPF0000018

    the first image you can see cracks in the ice that follow the dark material,
    the second image you can see the process in action, dark material being ejected,
    the third image (this patchwork image) the ice has melted and the residue is lying on the ground (you can tell this maybe because the dust is covering boulders)

    Well thats my crazy theory 😃

    edit.
    was wondering how the patchwork shows residue covered boulders and fans/blotches show clean boulders, it could be due to the speed of the ejected material, in fans the residue is ejected at high velocity leaving clean boulders but the patchwork is released more in a slow chimney fashion due to the size of the fissure this allows the material to settle on the boulders.

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  • wolfango by wolfango

    I was wondering if the plume orientation can be used to determine the timing of the event. Plumes pointing in different direction and of different intensity can be used to determine the strength of the wind and the intensities of the hotspots. Is it possible that the wind is the cause of such event? Maybe a wind warmer than carbon dioxide ice manages to reach the space between the ice and the martian soil to sublimate the CO2. The vapour cracks the ice sheet in regular patterns from which the gases stream to the surface. The same vapour once on the surface is transported by the wind forming a volcano like plume under which the ice melts. Hence the contrast between the darker warmer plume against the surrounding icy terrain.

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  • Portyankina by Portyankina scientist in response to john_cooper_35@hotmail.com's comment.

    Hi John,

    Theoretically possible, but practically - we don't know about any subsurface CO2 ice. There is subsurface water ice, but it's a bit too cold for it to start subliming (-123C).

    Anya

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  • ianbutton1 by ianbutton1

    This link http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Sublimation_Of_Ice_In_Martian_Spring.jpg/1280px-Sublimation_Of_Ice_In_Martian_Spring.jpg shows both shadows of landform and fans from fissures - both quite distinctive.

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  • theoldgaffer by theoldgaffer

    http://talk.planetfour.org/#/boards/BPF0000003/discussions/DPF000077v this is a before photo, can see similar landscape under ice

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  • wassock by wassock moderator

    This area on the face of it looks to have a similar structure, minus the red colour http://talk.planetfour.org/#/boards/BPF0000002/discussions/DPF0000514 But looking closer the surfaces are quite different, in the white image there are lots of spiders with a few boulders visible (possibly) but on the red one not much in the way of spiders but lots of boulders. Are both surfaces ice? If so why the difference in colour?

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  • jellyhead by jellyhead in response to theoldgaffer's comment.

    Maybe it's not a before photo but an after photo? The geyser debris left behind from a melted ice sheet from a previous year being covered up by a new ice sheet? I guess it could be possible if there wasn't enough wind to blow away the original debris - if this was the case you wouldn't expect to see this over too many fans (as these indicate reasonably significant wind activity), but just over lines and blotches where the debris comes straight up and down (like your image and the one that starting this discussion).

    I haven't seen enough images to really make a judgement (or know enough about the underlying science) but does it necessarily follow that the same process that results in the fans/blotches is the same process that creates the spider channels? I can see the argument that the sublimation of CO2 ice under the ice sheets results in geysers that leave debris and that this process could possibly scour channels - but why do the channels radiate out from a central point? Are the spiders growing each year? Isn't it more likely that the geysers are the result of the ice cracking (similar to the glass picture in a previous post) and allowing the CO2 gas to escape and spiders are something else entirely?

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