Planet Four Talk

Why Are Spiders not Everywhere?

  • wassock by wassock moderator

    There are teeny weeny spiders and great big fat ones and all sorts in between, there are also areas without spiders which do have fans and blotches. If the theory of spider formation holds then anywhere that a vent occurs the beneath the ice there should be a spider forming. So why are there different 'generations' of spiders ? Does a 'flat' landscape showing only vents without any noticeable spiders, or only tiny ones, imply that the surface has only recently been ice bound in the winter or that the surface is 'new'? (or that vents have only recently started to form in the area)

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  • jellyhead by jellyhead

    Such a good question! I've been puzzling over how/why spiders form as well. I'm not sure that if follows that everywhere there is a vent there should be a spider, but presumably everywhere there is a vent there should be at least the start of a channel being scoured. I think an important consideration is the time that it takes to form a spider - Anya said that their estimate is 10^5 years! But that just means that in order to create a big spider the ice has to break up in the same way over the spider year after year - that makes sense if the CO2 gas in the channels are the sole mechanism for spider growth, forcing its way to the surface and carving deeper and deeper channels. I get that, but if that is the case, then how do the channels form in the first place?

    It strikes me that there are two mechanisms for ice sheet breakup and therefore channel formation. The first is, as said above, sublimation under the ice sheet, CO2 gas in the channels eroding them further as it vents. The second is the natural breakup of the ice sheet (the fissures that we've seeing?) maybe due to the ice sheet retreating at the end of the season? Having said that the second mechanism could also be due to sublimation of CO2 gas under the ice sheet but having a broader, less localised effect.

    Regardless of what causes the ice to break up, it needs to do it in the same way over many years in order to form channels. Maybe spiders form because, for some reason, the yearly 'overlap' creates spider patterns. Does that make any sense!? So in the image http://talk.planetfour.org/#/subjects/APF0000hkc the white ice bits that look as if they could be the start of spiders are more obvious features because there is already the start of a channel underneath?

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  • wassock by wassock moderator

    The point being that if a spider ought to form wherever there's a regular vent (for the last 100 thousand years) then they should be every where. This implies that where there are no spiders then there's been not venting at the surface OR its a new surface - this could be a simple as an area of sand dunes which would effectively be a new surface every year

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  • jellyhead by jellyhead

    Oh, I see. I didn't think there could be such a thing as a regular vent, because the ice cap at the South Pole is seasonal? I must admit I had assumed that the whole ice cap retreats but maybe there is a permanent layer in some areas?

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  • wassock by wassock moderator

    Mean that if there is a vent which taps into the spider, somewhere, every year

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  • mschwamb by mschwamb scientist, translator

    This is something we're hoping to try and answer with this project. A future stage of this process will be to look at classify the different types of spider-like terrain. It could have something to do with the compactness of the soil and the topography. The brittleness of the ice is probably another factor, if it is stronger then you may form spiders if it's weaker the gas may escape before carving channels.

    Cheers,

    ~Meg

    Posted

  • Kitharode by Kitharode moderator

    Excuse me whilst I just pinch that bit about topography (for elsewhere). Ta.

    Re: Polar icecap - "Recent space missions then suggested that the southern ice cap, existing all year round, could be a mixture of water and carbon dioxide." (my bold). From here: http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Water_at_Martian_south_pole

    Worth a visit. Only one page, but very relevant (I think).

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  • Portyankina by Portyankina scientist

    Oh, so this is the thread where wassock's spider question was answered. Thanks, Meg!

    I just want to add 2 small things.

    for wassock:

    If vents repeat themselves on the exact same positions from year to year is another point we'll have a look at in this project. I'm pretty sure that say they do not. But let's see.

    for jellyhead:

    all the areas we show in this project are inside the seasonal cap, the one that retriats every summer. There is a permanent south cap, that you can easy see it on global maps of Mars or even with a good telescope (the one that can resolve Mars's disk) - bright cap slightly off the pole with spiral arm reminding you of galaxies. That cap is mix of water ice and some CO2 and way to permanent for me to be interesting 😃

    Anya

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

    Hi Meg. Is there an explanation anywhere on how spider's actually begin? I can see them developing fine once they get started but how do they get started and why do they radiate outward/inwards to a central point, why not random joining of channels? If we know what it is that 'initiates' the spider growing process, does this tell us something about why they can't get started everywhere?

    I guess I'm coming at this from a slightly different perspective to Wassock, so instead of why are spiders not everywhere, I'm still wondering why they are anywhere!

    Will post on the ask as scientist thread as well.

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  • Kitharode by Kitharode moderator

    This is a brilliant thread guys - congrats. I hope you eventually find/ discover/ work out the answers to these two (in my opinion) well thought out and important questions.

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  • BlueMoon58 by BlueMoon58

    Good question... Not many impact creaters in this region or large rocks either. There has been some suggestion that the Fans and Blotches have some connection with these Spider like features. If indeed these Spiders and Blotches are as a result of CO2 escaping under pressure from below the Ice how come we dont see Spiders here on Earth. We have ICE we have VOLCANIC activity beneath the ICE. We have GEEZERS and WATERSPOUTS, GAS vents of Methane & Sulphur. It makes you wonder

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  • Kitharode by Kitharode moderator in response to BlueMoon58's comment.

    Obviously wildly different, but perhaps of some interest: http://en.wikipedia.org/wiki/Spider_crater

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  • mschwamb by mschwamb scientist, translator in response to jellyhead's comment.

    It's a good question. I don't actually know the answer. Maybe Anya and Michael can say more.

    Creers,

    ~Meg

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

    Have a look at the "Spiders thread" - make a cup of coffee first though

    Posted