Planet Four Talk

Muck about with this one then

  • wassock by wassock moderator

    This is a crop from the HiRise grey scale image http://hirise.lpl.arizona.edu/PSP_003720_0930

    Waddayamakeofthatthen? The whole area of what looks at first glance like a network of "fans from cracks", which on a closer examination may not be, honeycombed with empty (of fans) spaces some of which contain spiders like this and others what looks like the same sort of lined/cracked surface as that producing the fans

    enter image description here

    enter image description here

    Posted

  • wassock by wassock moderator

    Not the same area but nearbye Have a look - fans appear to be associated with the outer edges of the spiders here

    http://www.uahirise.org/ESP_012488_0930 26 March 2009 - Distinct halos of fans around many of the spiders

    enter image description here

    http://www.uahirise.org/ESP_012633_0930 6 April 2009 - those halos have faded!

    enter image description here

    Posted

  • Kitharode by Kitharode moderator

    If nothing else, we're getting good at this "more questions than answers" game. 😉

    From Anya's plot map in 'Spiders by Location' it looks like they're in the Agelenopsis Region (Lat -87 and Long 129E). The area is on the SPLD's with a thickness around 2.5km.

    In appears to me that as we move from top to bottom in the HiRise images, there is increasing undulation/deformation of the surface. There seems to be an increase in the number of spiders as the undulations increase. I would suggest that in the lower part of the images the spiders become more 'lined up' within/along the undulations. I also get the impression that the spiders become more elongated (longer than they are wide) as we move from top to bottom of the images.

    Whadyamakeathatthen? 😛

    Posted

  • Kitharode by Kitharode moderator

    Nearby in Manhatten (2007): http://hirise.lpl.arizona.edu/PSP_003746_0935

    Posted

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

    Do you make those fans out as radial from the bottom left? - deffo not all pointing in the same direction. Same sort of thing with the cracks and the spiders tho'

    Posted

  • Kitharode by Kitharode moderator

    Can't say I've noticed radial fans. Can you give us a 'crop' to show example?

    Posted

  • wassock by wassock moderator

    Look at the greyscale jpg the crop would be the whole thing. The fans along the bottom right edge of the image are not far off parallel to the edge, the ones top centre are some way off that and there's a gradation between the 2

    Posted

  • p.titchin by p.titchin in response to wassock's comment.

    Is this somwhere around chasma Australe. If so, ?katabatic winds, They often curl. ~ Pete

    Posted

  • Kitharode by Kitharode moderator

    Yes, I see it now and I agree. Change of direction indeed. It doesn't look to me like a wind effect (might be wrong) so I'm more inclined to think 'lay of the land'. We know from your Bendy Winds thread, and from Inca City, that slope can be a major player in fan direction. There might be a curved, gently sloping terrace between the spidery regions to left and right in the image.

    The middle of the image is very polygonal, which I'm thinking is 'cracked ice'. Perhaps earlier the whole image would be like this, but the 'lay of the land' means this area takes longer to sublime (?) There are spiders in this area, but they appear to be small (or don't appear at all) because, I think, they are still covered by this polygonal ice. My guess would be that an ice-free image would show spiders in this area. I'll see if I can find one.

    If it were true that there are spiders under this ice, if ice it be, this raises a number of interesting questions methinks. Not least of these would be; If venting makes spiders, why don't we have polygonal spiders here?

    Posted

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

    PS: Had a rethink about polygons in ice. I was thinking about your observation that when we see venting spiders they seem to vent more towards the ends of the 'legs', rather than the centre. The more I look, the more I see that this is the case.

    So I have this 'image' in my mind of an area with a whole bunch of spiders beginning to vent at the end of their legs. The area is still covered with ice, but we see the start of the fanning process. What we see therefore is a whole bunch of polygonal-ish fans (the leg ends), with a clear central bit, giving the impression of ice polygons. Does that make sense? If it does, it allows for polygon fans in icecover without the need for polygon spiders.

    Posted

  • Kitharode by Kitharode moderator in response to p.titchin's comment.

    Pete: It's kinda near to it, but I wouldn't call it close. It's also pretty high up on the SPLD's, altitude wise, so I'm thinking the katabatics might not have got going in the area. Good point though. And because I know nothing about the katabatics really, anything I say about them is best ignored. 😃

    Posted

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

    It seems obvious/self evident to me (although this may not actually be true due to something I've not thought of) that if the fans are long and thin then they can only have their direction determined by slope if either the gas is venting fairly slowly so that the dust effectively 'falls' down the slope, or if the direction of the vent is normal to the slope of the surface it is in and the gas/dust comes out fast. AND both must happen in still air/ with a constant wind aligned with the direction of slope. For the latter to be true pretty much all of the vents over the whole area must be similarly aligned wrt the slope at the vent point and I just don't see how that works.

    If the direction of the fan was dictated by the slope of the land then you could only get nice long thin AND symmetrical fans if there is no wind sheer across the direction of the fan. If there is any wind crossing the path then the resultant fan Must be distorted and I don't see that here.

    My perspective of this image (and of the others under "Bendy Winds) is that we are seeing an image of the weather system in place at the time that a venting episode occurred across the whole area. Think of the weather forecast where they show the isobar charts showing the approaching weather systems. The isobars don't follow nice straight lines across a given area but bend around the lows and highs on the pressure plots and the winds flow along the lines of the isobars. What you are looking at here is an image of that weather map on mars at the time the vent was going on - figure out how fast such systems move and you can work out how long the venting went on for, or conversely figure how long they vented and get a handle on how fast the weather systems move.

    As I said at the outset this seems so obvious to me, but I suspect I may need to draw some pictures - may have to revive the Bendy Winds thread.

    Posted

  • Kitharode by Kitharode moderator

    I for one can't find anything wrong with your thinking. I agree that much of what you say seems to be the logical thing to think. Yes, back to the Bendy Winds might be fruitful. For that area, which I seem to remember being very large, wind would seem to be a better option than slope. It'd be good to get a handle on the lay of the land there to see if it could be ruled out as a major player.

    Inca City is different I think. It'd have to be a very strange wind that moved fans in four directions at once. There's some images that show all four walls of a zone 'dripping' dust towards the central floor. I'm with slope there.

    Now it's back to Micheal Fish for a weather update. 😉

    Posted