Planet Four Talk

Veins!

  • Scobes by Scobes

    Any ideas what the vein like markings are?

    Posted

  • PaulMetcalfe by PaulMetcalfe in response to Scobes's comment.

    Hi Scobes,

    These are generally referred to as 'Spider Legs' and in general they will radiate out from a central point - the whole thing being referred to as a spider. They are basically channels or depressions dug into the surface, probably by flows of gas beneath the ice sheet.

    There appear to be 10+ spiders here. There should be plenty of talk on these boards about spiders.

    Paul

    Posted

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

    Hiya,

    They do look like veins. Those are 'spider' channels, they're carved slowly over time by carbon dioxide gas trapped below a semi-translucent melting ice sheet. You can learn more about the spiders and how they form here and on the project blog.

    Cheers,

    ~Meg

    Posted

  • Mote by Mote

    So many questions... after reading the link and the blog post and a few other spider formation descriptions from years past, I am still wondering if the observed channels are only in the bottommost layer of the surface structure. Is the seasonal co2 deposit not reaching the channels, and/or not filling in the channels? Are the channels ever being filled in? How are the channels filled in and capped each year. Do the channels under the cap ever meet an edge of the cap? Are the channels also causing sublimation/erosion into the underside of the cap, making a tube? Is there a deposition or anti-sublimation period in the gas layer? Is there any indication of channels being filled and not subliming- forming anti-spiders? Are there channels sublimed/eroded solely into the topside of the topmost co2 deposit layer? Which direction is the flow of gas per day and per season, or does the vented material ever go back into the hole to fill the spider back up, and is that why some araneiform channels are dark?
    I realize that many of these questions may not have answers yet, and I am still catching up on the discussion posts, and that this may not be the right time or place for finding these answers, but any additional information would ease the cravings of the monkey on my back that's causing my brain to desperately need many 3d moving pictures of this process in respect to various terrain, time, and circumstances.
    My very basic understanding is that there is a more dense base layer of some material called "the surface" into which there are spiders being carved by a layer of gas and dust movement that is under a ~1meter-11meter layer of co2 ice that is semi-translucent and semi-permanent and dense enough to be a non-subliming cap, which is then being deposited onto by an annular co2 frost cycle- is that close to being correct? I misunderstand easily and I am a very visually/spatially oriented learner, words become pictures and tend to lose their intended meaning, so I am only asking for help. The "it depends" statement seems fitting; is there a diagram or 3d rendering of all the various possibilities floating around?

    Once again, Thank You

    Posted

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

    I can't get to all of this now. A bit busy at the moment. I'm at the American Astronomical Society meeting in Seattle, but Anya, who's on the Planet Four science team, has been studying spider formation. It looks like the spiders don't change depth on the time scales they've been monitoring and there is evidence they get dug over 100s of years type scales.

    There are definitely fans that form/cracks in the ice producing geysers in areas where there are no visible spiders. If there are spiders, geysers/fans do tend to emerge from the channels. The trend trend is there, may because of light reflecting off the edges of the troughs.

    One of our science team live chats we talked about this. I can't recall off the top of my head which one discussed this. You can find the video from both here and here.

    Cheers,

    ~Meg

    Posted

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

    Mote

    When you see reference to the cap we are mostly referring to the seasonal cap of C02, nominally about a meter thick through which the vents form and onto which the material forming the fans and blotches falls. This is a seasonal cap which forms during the winter and then disappears during spring/summer. As distinct from the permanent ice cap which is much thicker and is in some areas the surface beneath the seasonal cap and persists the year round. When thinking about the permanent cap you need to not picture the antartic at home, the ice here is dirty and full of dust and is overlain by a layer of dusty material.
    Beneath this is mars/ground/grust/the surface. for most of the areas we're looking at this is thought to me a 'reogolith' comprised of a mixture of dust and CO2 ic and maybe a bit of water ice, and a lot of the time this is ontop of the permanent ice cap.. All but the top most layer (of undetermined thickness) is essentially in a state of permafrost. Much of the surface cracking and the polygonal terrain is the result of shrinkage of the ground as the entrained ice turns to gas and departs the scene.
    I think many of your questions above are null when you understand that the 'cap' isn't there all year round and the spiders are in the topmost layer of 'Mars' upon which the seasonal cap forms. Thus the spiders are beneath ice when the fans are forming and open to atmosphere come summer.
    There are pictures of all this, take a look at the Blog

    Posted

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

    Hi Mote. This diagram might help with some of your questions: http://www.nasa.gov/images/content/171411main_pia09224-thick-annot-516.jpg

    It shows the South Polar Layered Deposits (SPLD). The black background is the 'true' rocky surface of Mars. The SPLD's are layers of ice and dust laid down over (probably) millions of years. The black outline shape in the upper left quadrant is the permanant ice cap. For this discussion we can take the spld's and the ice cap as permanant features.

    The seasonal icelayer which forms in winter and disappears in summer covers the whole of the diagram, and more, to around -60 deg latitude. Most spiders and fans are found between latitudes -75 and -85. Therefore spiders (for the most part) are channels in the topmost layer of the spld's.

    Another useful diagram showing the locations of spiders is at the bottom of page 1 in this discussion: http://talk.planetfour.org/#/boards/BPF0000008/discussions/DPF0000f2j

    That's not gonna get rid of the monkey altogether, but it may make it a little lighter to carry. 😉

    Posted

  • wassock by wassock moderator

    Nice 2nd link Kitharode, I'd forgot about that one and so I' boosted it to "Featured" staus so it stays visible. Mote - the red outlined area is known as "Cryptic" as I understand it this is because the temperature within is a lot colder than it ought to be and this is thought to be because there's a lot of ice hiding beneath the surface

    Posted