Planet Four Talk

Subsurface Glacial Activity

  • Muse2k8 by Muse2k8

    The cracks themselves appear in a glacial like formation. While on earth crevasses are deep cracks forming in glacial ice due to movement, for the purposes of this theory it will be taken that this glacial ice needs not be pure (by which any ice content is acceptable). It should probably be noted that while there are references to ice and water, this would be most likely as Carbon Dioxide.

    While it appears that the surface area of Mars is no longer moving (no tectonics) the cracks form upon a wide open surface as opposed to a long traverse such as a typical glacier. As such the workings themselves need to be modified.

    Mars is itself a small planet whose orbit takes a more elliptical route around the sun than the earth does. At the point Mars reaches spring in its southern hemisphere, the planets orbit takes a closer approach to the sun. While there is no observable geological activity taken place on Mars any longer (such as volcanic activity) it would be easy to assume that there is no activity at all taking place. However as can be observed most notably in the Galilean moons of Jupiter, some stretching and relaxing of the celestial body can occur due to fluctuations in gravity. As Mars orbits elliptically around the sun it seems only fair to assume that although Mars is a much larger body than Europa, that some slight activity could occur.

    Now taking further the idea that below the surface of Mars there is a strong likely presence of ice; and this is indeed highly feasible given the porous nature of many rocks, the low temperatures and of course the presence of polar ice caps; we can come to the conclusion that we have differing layers within the surface of Mars. Above we have a layer of rock and below that we have a layer of ice. This ice will not be pure ice but ice formed within rock itself.

    Now as the compressible nature of rock and ice differs, the idea forms that while the planet is being stretched, the rock layer itself moves at a differing level to that of the ice layer below it. As the rock layer moves we have friction occurring (dry friction). As this process generates more heat energy the ice layer below begins to melt providing us now with a third layer of water and lose rock akin to that found under a glacier. In essence what has been described is the process of glacial drift turned upside down with the ice below the rock instead of the rock below the ice. From this process the friction becomes that of lubricated friction allowing a much more freely moving surface.

    At this point now as Mars moves into spring and the planet becomes slightly stretched, the results of friction and solar energy combine to form not just one potential feature but two.

    As the water expands under the rock from the extra energy it contains (and of course as water is not compressible) there needs to be a route of escape. In the process of the geyser activity, the surface rock layer is strong and stable forming only slight cracks and escape tunnels. This energised water (potentially gaseous at this point) pushes through these fissures and exploding into the atmosphere carrying with it the dirt, sediment and trapped elements from below (we can see this from the high content of CO2 in the geyser activity. Of course the water content itself may not necessarily be H2O but could indeed be frozen Carbon Dioxide, if not more likely).

    However in the formation we are looking at with the cracked surface this could be either a more brittle rock (the potential that this could even be sedimentary is exciting) or more likely a rock formation containing ice itself, although to a much lower level than the layer below. If this layer is indeed mostly of permafrost this could then explain potential for the rock to repair itself by melting back together. As energy escapes through this layer and combined with the stretching of Mars this could easily explain the crevasse style cracking and movement that has been observed.

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  • Muse2k8 by Muse2k8

    Have a look at images of ice cracking over water (e.g. sea ice, pond ice etc) they give this kind of pattern. As rock is more stable than ice then there is less cracking occurring, however the pattern is very similar.

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  • michaelaye by michaelaye scientist

    The tidal forces of the Sun on Mars are far too small to do anything to it, because the influence diminishes with the inverse square law. Even for the Earth the Moon is the dominant player for tidal forces, not the Sun (see here: http://hyperphysics.phy-astr.gsu.edu/hbase/tide.html#mstid). While in it's essence some parts of your hypothesis seem workable, we have to go for Occam's razor here and our more simple (at least we think) model (explained here http://blog.planetfour.org/2013/01/07/mars-fan-club/) so far works very well. (http://onlinelibrary.wiley.com/doi/10.1029/2011JE003917/abstract)

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  • Muse2k8 by Muse2k8

    I did have a look at the maths and it did seem to be a small influence. Astrophysics isn't my specialty. However at the distance Mars is from the sun and thus the energy imparted, it doesn't seem to me that this alone could be responsible; especially when you consider that the planet is coming from a winter phase which will result in even less heat energy. Even with the possibility of refracted light through a transparent ice level. CO2 forms a gas at about -57C (sublime at -78C?). Given the atmospheric pressure and depth below frozen ground I just cant see that the Sun alone could give the CO2 enough energy to do this. As such I looked at another possibility, maybe not through tidal forces but some other force resulting in the friction which would create more than enough energy.

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  • Muse2k8 by Muse2k8

    No follow up?

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  • Kitharode by Kitharode moderator

    Hi There. Congratulations on a thoughtful, well written, and stimulating first post. I sincerely hope you get many follow ups. (I've not seen too many Science Team names around, so perhaps we've already worn out the first shift. I'm definately giving you a 'Follow', because I'm genuinely interested, but I doubt if I'll be contributing much - you seem to have it under control. Cheers.

    PS. Your title was interesting. But with my passion for ancient Greek music, when I saw that the author was Muse... need I say more?

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  • Portyankina by Portyankina scientist

    Dear Muse2k8,

    You have created a very complex hypothesis, unfortunately on several wrong premises. We know that:

    1. these cracks are formed in the CO2 ice layer which is not more than 1 m thick. We know this from repeated observations of the poles with cameras and spectrometers.
    2. the dessicated layer of regolith (i.e. what you call rock) is very thin at these latitudes, as few as several tens of cm. We know this from the Mars Phoenix lander.
    3. there is no subsurface reservoir of clean water ice. There is a constantly changing proportion of ice collected in pores of the regolith. We know this from radar subsurface sounding data.
    4. at the average martian pressure of 4 mbar CO2 sublimes at 146K (-123C) - here one has to be careful, however and take into account variations of pressure due to seasonal changes. But you can always count on that martian atmosphere is 95% CO2 and hence any surface CO2 is in equilibrium with it - this means it will sublimate with ANY incoming energy.

    Also I am not sure what this sentence means: "Given the atmospheric pressure and depth below frozen ground I just cant see that the Sun alone could give the CO2 enough energy to do this." - what depth below the frozen ground? The layer that subject to stress is on top of the surface. Must be some misunderstanding here.

    Anya

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  • wassock by wassock moderator in response to Portyankina's comment.

    Anya, any numbers for how much pressure can build up beneath the ice? The areas with the surface cracking seem to have fairly even terrain underneath. Would it be possible for gas to build up under a large area of ice such that it gets lifted by the 'bubble' and consequently cracks?

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  • Portyankina by Portyankina scientist

    I made such a calculation several years ago. The problem with it is A LOT ASSUMPTIONS you have to make. Like, how much heat gets lost into the ground (i.e. assumption of thermal properties of regolith), how easily the top surface is compactable, or if you build pressure under the ice layer, how much of it goes through the pores in the ground, how clean is the ice layer and what ice form it's in. So, there is no one number that I could give you. And on top of this, our understanding changed since then and I really would liek to re-visit this calculation. If yo want to see it, I can give you my paper from that time.
    I think, if anywhere there is a possibility of a gas pillow (or levitating ice layer) - it's these areas with ice cracks. The surface here is smooth, which give a way to creating uniform ice layer - this I think is important for such a scenario.
    Anya

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  • wassock by wassock moderator

    Yup - I think that the thickness and nature of the dust beneath will also have have an effect. In amongst the dust there will be space for the dust to gather, more so than if the ice sits on bare rock, and if you have a gas/dust mix the it will have different thermal properties than just gas - might be ablr to stay 'warm' better? Wouldn't mind a look at your paper if you've time to forward it.

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  • Muse2k8 by Muse2k8

    My hypothesis was built originally on the idea that there wasn't a pure layer of ice on this part of the surface and that gravitational effects (tidal activity) resulted in some small friction which generated the required heat to sublime the CO2. Certainly with a thin icy layer over the dusty rock layer and taking into account atm I can see how the CO2 will heat up sufficiently to form a layer of dusty gas under the ice.

    So am I right in thinking then that the ice builds up over winter, when the more directed solar IR hits the planet in spring, this raises the temperature below the ice sufficiently to sublime the CO2. This gas (and clearly dust) adds pressure below the ice till the layer becomes sufficiently weak enough for the gas to push through. This forms thin cracks (similar to sea ice on earth during arctic spring; tap a pane of glass with a hammer) allowing the gas and dust to evacuate. The result is CO2 gas escaping under pressure thus forming these fans etc (dust particles giving them a dark appearance).

    As summer comes the ice layer reduces and there is no longer any gaseous pressure from below and thus the venting stops. The dust settles back and everything becomes set for another cycle.

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  • Muse2k8 by Muse2k8 in response to Kitharode's comment.

    Ha ha thank you Kitharode 😃

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  • Portyankina by Portyankina scientist in response to Muse2k8's comment.

    Yes, your understanding of the process now sounds very accurate!

    Anya

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  • Portyankina by Portyankina scientist in response to wassock's comment.

    Wassock,

    Here is the link to journal page with the article I was talking about: link

    I am not very good with copy-paste laws, I am afraid I can not put it to publicly available place. I can share it with you personally though, so let me know by email (portyankina (at) gmail.com) if you can not get it from the link above and I'll send it to you.

    Anybody else is welcome to do the same.

    Anya

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