Planet Four Talk

Examination of the Fans Evident in the region around Latitude -85.4, Longitude 103.9

  • wassock by wassock moderator

    All the images which follow are taken from HiRise Greyscale .jpg images, map orientated., and show the same area of Mars. Although they do not all present the same size or orientation of area the central portion of each is of approximately the same location. In total there are around 40 imags available on HiRise of this location at different times.

    This will be a big post so please hold off commenting until it's all up please

    Posted

  • wassock by wassock moderator

    Sorry for break, windy city and all. Some of the images following are chopped by the page formatting, but the HiRise ref is on each - just search HiRise for the ref number if you want to see the whole thing.

    Examination of the Fans Evident in the region around Latitude -85.4, Longitude 104.9

    All the images which follow are taken from HiRise Greyscale .jpg images, map orientated., and show the same area of Mars. Although they do not all present the same size or orientation of area the central portion of each is of approximately the same location. In total there are around 40 imags available on HiRise of this location at different times.

    The first 4 images are from 4 different Martian years taken in 2007,2009, 2011 and 2012 and all are early in the martian spring with solar longitudes between 181 and 192. All 4 images show many mfans and the predominate direction of the fans is to the North. This consistent early season wind direction may be evidence of a katabatic wind from the southern polar regions.

    27 Feb 2007 SL (solar Longitude) 191.2
    enter image description here

    1 Jan 2009 SL 183.7
    enter image description here

    20 Nov 2010 SL 184.5
    enter image description here

    1 Oct 2012
    enter image description here

    Posted

  • wassock by wassock moderator

    The next images are slightly later in the year, solar longitudes from 206 to 211, approximately 1 earth month later than the corresponding images in the first set. The northward fans are still visible but there are now 2 other populations of fans. One set on the right( East) of each image has many fans pointing to the NorthEast of these many can be seen to share a common source point as the original Northward fans. The second population is on the right of each image but these fans are directed toward the South. Each of the following images shows a very similar pattern of fans even though each is from a different year.

    1 Apr 2007 SL 210.8
    enter image description here

    11 Feb 2009 SL 207.9
    enter image description here

    27 Dec 2010 SL 206.3
    enter image description here

    15 Nov 2012
    enter image description here

    Posted

  • wassock by wassock moderator

    A third set of images, solar Longitude 259 to 269 shows the same arrangement of fans which become progressively darker and larger as the sun gets higher in the sky. The change between the two 2013 images is very apparent and shows there has been a comparatively rapid change in the 15 days between the 2 images. However it can be same that the pattern of fans remains the same, those on the left blowing to the south and those on the right to the West or Northwest.

    18 June 2007 SL259.7
    enter image description here

    6 Apr 2011 SL 268.7
    enter image description here

    6 Feb 2013 SL259.3
    enter image description here

    21 Feb 2013 SL269
    enter image description here

    Posted

  • wassock by wassock moderator

    The pattern of fans for this area occurs in each of the 4 Martian years represented by these images. Early season fans have a Northward direction and later fans have a southward direction on the left of the area and North/NorthWest on the right. The images available do not show which of the left and right fans develop first, both sets are evident in images from Solar Longitudes of around 206 onwards. Both sets of later fans start out as fairly narrow fans and develop with time into wider, darker fans eventually covering much of the surface in their respective areas. But it is important to note that both these sets of fans maintain their orientations throughout this process with little in the way of multiple fans evident in either area. This makes it appear that the left and right sides of the area are subject to different wind directions and that these directions are fairly invariant (whilst the fans are being formed at any rate).
    Whilst the later fans develop and grow with time it appears that the initial. Northward fans, do not change with time keeping the same form as when originally formed.

    These observations appear difficult to explain. The differing orientations of fan formation on either side of the area could be due to the fans following the lie of the land, their shape and direction caused by the slope of the landscape. However this is difficult to accept in the light of the early season fans which are aligned to the North. It is possible that this could be explained by a strong wind overcoming the effect of local topography but the Northward fans are all symmetrical and any topographical effect strong enough to give rise to the later season distribution of fans would surely cause deformation of these early wind blown fans. The notes on the HiRise site accompanying image PSP_003364_0945 (http://www.uahirise.org/PSP_003364_0945), which is the same location, indicate that the area is actually fairly flat and that topographical effect are not though to be responsible for the differing directions of the fans.
    These notes indicate that the differing directions of the fans are due to the wind changing direction as the different fans are formed. In the light of the consistency of direction of the different populations of fans both through each individual year and from year to year makes this also a difficult concept. It would require the wind to blow one way whilst one set of fans is formed and then in another direction for the second set. And the wind only blows in the respective directions when the fans are venting as there is little evidence of other wind direction in either area once the main fans have started to form.
    Another explanation would be that the 2 sets of fans to the left and right are caused by separate events early in the season the differing wind directions caused by a repeating shift in wind direction caused by the cessation of the winter katabatic wind at the time that the sun first rises. For this idea to work all the material evident in the late season images would need to have been ejected in the initial early season events and then develop as the season progresses. Perhaps the early season fans are comprised of a mixture of free particulates and a dirty snow mix of particulates and ice. If the individual dust particles in this snow were encapsulated in condensing ice in the plumes the dust would gradually become visible as the ice melts. This explanation avoids the need for a repeating pattern of winds throughout the year synchronised with the venting events in the different locations, but also requires most of the ejected dust to be vented early in the season in a single event at each vent.

    Enjoy - off on hols for a week from Sunday so will see how this is going when I get back

    Posted

  • Kitharode by Kitharode moderator

    It's going rather slowly. Lots to think about. Great presentation Wassock - Well done.

    In your second post, one of your 4 chosen years is 2001. Should this be 2011?

    You've certainly uncovered a very weird situation here. The more I study the images, the more confused I get. I've nothing sensible to add to your comments so far, but I'll be having a think about them.

    Posted

  • bobwiersma1322 by bobwiersma1322

    I have seen similar structures in the shallow ocean around sand dollar beds where moving sands flow through the sand dollars leaving trails. I have no idea what these could be but they are interesting indeed.

    Posted

  • wassock by wassock moderator

    Kith, cant seeanything labled as 2001, were you seeing things?

    Bob, we're fairly clear on what we think is causing this - wind blown dust from "geysers". The repeating nature year on year and the way they develop challenges (I think) some of the models for how it all works though

    Posted

  • wassock by wassock moderator

    Anyone care to confirm that the pattern does appear to repeat each year. Seems obvious to me but would like to confirm that I'm not just joining the dots to get the answer I'm looking for.

    Posted

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

    From your second post above: "...taken in 2007,2009, 2001 and 2012..."

    I would agree that the pattern seems to repeat.

    Posted

  • wassock by wassock moderator

    Ok seen and corrected. Each image is labelled with the correct year though.

    The pattern repeats and it seems that the order of formation repeats as well, I can live with that being down to a repeating seasonal weather pattern. What is troubling is how the different sets of fans appear to grow as the season progresses AND maintain their differing orientations. That requires both several cycles of repeating weather and some degree of synchronisation with eruption events in the different areas.

    Posted

  • mschwamb by mschwamb scientist, translator

    You might want to think about the topography in the images and how that will play a role.. To me it looks like this is a dune or something kind of raised hill and that is behaving different than the lower areas,. It looks to me like the fans are blowing downhill on the dune/hill and then behaving differently elsewhere.

    Cheers,

    ~Meg

    Posted

  • wassock by wassock moderator

    Meg this is the area reffered to in Candy's "blowing in the wind" post on HiRise (I think) which indicates it is fairly flat. If it were true then some of the fans at the multi direction sources would be distorted because the slope would "pull" the fan one way and the wind another.

    Candys post here - http://www.uahirise.org/ESP_011934_0945

    Posted

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

    The MRO site has a MOLA topography map for each image and 'your' area of interest looks far from flat to me. I'm not saying it explains everything, but I think bumps and slope have a part to play here. http://viewer.mars.asu.edu/planetview/inst/hirise/ESP_011934_0945_RED#start

    Posted

  • wassock by wassock moderator

    How does the HiRise image relate to tge Mola interms of orientation and is there a way to figure out tge scale of the topography?
    Either way up my reasoning is that if slope were a big enough factor to cause the large, later season fans (regardless of wind direction) the the slope should also affect the early season northish fans and pull them slightly downslope making them assymetric. I dont see this effect ergo slope isnt causing the fans

    Posted

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

    I'm pretty sure (but confirmation would be good) that MOLA images have South at bottom of image - the opposite to HiRise.

    I did ask the Mola scientists about scale (via their contact link) but never got a reply. 😦

    Posted

  • michaelaye by michaelaye scientist

    Hey Kitharode, please post your scale question here!
    About south/north: The chosen direction for display of a remote-sensing mostly depends on it's processing stage. It just happened to be that we just took straight shots from the HiRISE camera in a so called 'unprojected' level. It made things easier at the time we started P4.
    MOLA images are mostly being distributed in their 'end-product' stage that show their map-projected version. And yes, it is common to project images with north being up. Mind though, that if you have the south pole inside your current image shown, that is not very meaningful! πŸ˜‰
    If you try out the other HiRISE products on the respective webpage, you should find a version that aligns well with the MOLA product.

    Posted

  • michaelaye by michaelaye scientist

    Also, be aware, that a very few HiRISE images used here are taken on the other side of the orbit, so from south to north. So don't get confused when you see different things. This is especially true for Inca City season 1 that just went live.

    Posted

  • wassock by wassock moderator

    Michaelaye, so how does that make the mola image kith posted relate to the hirise images which are the subject of the thread? Are they all in (vaguely) the same alignment?

    Posted

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

    Michaelaye. New discussion on image scale on this board. Ta.

    Posted

  • wassock by wassock moderator

    OK let's look at 2 of the 2013 images in more detail - the same thing shows in each of the 4 years though.

    In the first there are 2 main populations of fans. Top right we have fans towards the north (12o'clock) and to the North East ish (1:30). Th 12 oclock fans are formed first each year. The other population, bottom left, is mainly made of of 6 oclock fans with a few 9's, 10's and very few 12's. In other years this population does have a number of 12 fans.

    6 Feb 2013 SL259.3
    enter image description here

    In the second image, dated 15 days later, both populations retain their respective directions but the 1:30 and 6 oclock fans have all grown, as have the mid range fans which have directions intermediate to the left and right populations.

    21 Feb 2013 SL269
    enter image description here

    The standard model has the increase in size of the fans caused by repeated eruptions. If the fans are caused by wind action, then this model requires the subsequent eruptions to be synchronised with the same wind direction each time and for the wind direction to be markedly different on the left and right. The differing directions could be caused by still air events on sloping terrain but the apparent symmetry of the fans in all directions indicates that slope does not have a major effect on the direction of the fans.
    My explanation of this is that all the material visible in the later image is already there in the first, just not visible,and that the fans "develop" with time as the surface conditions change.

    Posted

  • Kitharode by Kitharode moderator

    All good stuff as usual. Can you tell us more about your 'fan development' idea?

    Posted

  • wassock by wassock moderator

    Ok, one idea would be that as the dust erupts the co2 around it cools rapidly as the pressure drops forming snow/hail each bit freezing around a particle of dust. Snow works best for this, the fluffy bits travelling furthest down wind. Said snow is then not visible against the ice until it sublimes leaving behind the dark dust.

    Another thing against tge fans being slope formed is that to get the 2 directions on the ldft and right sides you need them to be formed in still air. If this were the case then the fans would be off center blotches rather than classic fan shaped. There is a paper which models a still air vent producing a proper fan, but this requires a high velocity venting AND the vent to be perpendicular to the surface slope. This seems unlikely for all the fans in the image.

    Posted

  • michaelaye by michaelaye scientist

    • The 'standard model' also includes changes in wind strength during a 2nd later eruption, explaining an increase of fan length.
    • Our simulations say that the area where CO2 condensation on the dust seeds is possible (the right set of thermodynamical parameter values) is only very close to the vent, so we are currently having our doubts that CO2 snow jets are at all possible, because the condensation needs time, while the dust is travelling pretty fast through the zone of the advantageous parameters.
    • I don't understand why I need the fans being formed in still air for the visible directions? Assuming the wind comes from the upper left and the bright part is a ridge (did anybody check if we have a DEM at this location?) then going with the wind but falling downwards on both sides of the ridge should look very similar to this, shouldn't it? Maybe I'm missing something?
    • We have no data on the breaking physics of large continuous CO2 ice blocks so I guess it's okay to assume that not all jets are vertical, but I wouldn't bet on it. πŸ˜‰
    • We really need to look at an elevation map to understand this area.

    Posted

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

    "DEM at this location" - What's DEM?

    Does a useful elevation map for the HiRise images exist?

    Posted

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

    OK taking those 5 points in order:

    1 that's fine for 1 or 2 or many fans where they all have the same direction/combination of directions. What we have here are 2 populations of fan sources producing fans in different directions the size of which grows with time but each set true to their original direction. So for this to work we need the wind to blow in different directions at either end in syhncronistion with the eruption events. The 2 sets of fans both grow as the year progresses and keep their same directions, the individual vents also have early forming fans which are in a different direction to the ones which grow. And the same pattern has happened in each of the 4 years we've looked at. I can accept a repeating pattern of winds related to the change fron winter to spring to give the initial set of fans directions, but for the winds to shift in concert with different vent events over a season seems less easy to accept and for the same thing to hsppen 4 years on the trot would stretch the credule.

    2 I was thinking along the lines of adiabatic cooling of the gas as it expands out of the vent, which produces co2 particulate with dust it it rather than using the dust as a seeding mechanism.

    3 If we can get a single weather system which can provide such a range of wind directions over a fairly small area then that will work and may be the easiest idea but all will depend on tge lie of the land and how the weather works. Do you know how big a weather system (like an anti cyclone) eould be cw Earth, bigger or smaller or the same? The 2nd image above does bear some resemblance to a wind direction/isobar chart.

    Where im coming from on the fan shapes is this:

    Standard model for forming a vent is a still air eruption. The dust goes up spreads a bit and drops back forming a circle on a flat surface, any wind will distort this shape until none of the dust falls upwind of the vent point and we get our teardrop fan shape. If we hav a still air vent on a slope then the dust on the up hill side will have less distance to fall and spread until it hits the ground and so the perimeter of the mark will be closer to the source than for the flat terrain equivalent. On the down slope side the dust has further fall and spread and so some will travel further away. The effect when viewed from above would be a ellipse skewed downslope from the vent. If a surface effect can cause a classic fan shape (no dust uphill of the vent) then I have difficulty in seeing how a wind blown fan from the same vent in a different direction would also have the same shape. Unless the wind is VERY strong the wind blown fan will be distorted by the slope. This is key to the whole plot, if I'm visulising this wrong then my idea fails.

    4 Explaining the direction of the vents using slope and non vertical vents needs ALL the vents to be non vertical, and will only work if the venting is at high pressure, if the vents are more convection than pressure then it wont work either.

    5 with you on that one, do you have one any where?

    Posted

  • wassock by wassock moderator

    The three images below are of vaguely the same area from 2007, 2009, 2012 The HiRise Refs are PSP_003430_0935, ESP_011671_0935 and ESP_029578_0935. This area is one of those considered in the Hansen et al Paper "HiRISE observations of gas sublimation-driven activity in Mars’ southern polar
    regions: I. Erosion of the surface" published in 2009. Apologies if the scaling is a bit iffy, particularly for the top one.

    The paper uses the next 2007 image in the series after the one here to show haw changes in wind direction result in different direction fans in different areas. The paper also presents a cross section of the terrain across the central part of the image. from MOLA data. This area is best defined in the middle image and covers the area with closly spaced fans/blotches and the clearer area to the right of that.

    enter image description here

    go here for a larger version https://dl.dropbox.com/s/4isb85a6kwbh6zd/Combined rotations.jpg

    This is a cut'n'past from the paper, I think it's fairly easy to see how this relates to the above images. The top landscap is from an image earlier in the season when fan formation hadn't fully got going.

    enter image description here

    This is the area I've referred to in the "Bendy Winds" Thread previously. Again we have somewhat consistent patterns of fans in different directions - this time explained by the lay of the land maybe?
    If that is the case then what implication does it have for using the fan data to describe the weather? If it's not the case then we're back to why are all these fans reproducibly in different directions? Enjoy

    Posted

  • wassock by wassock moderator

    The image relating to the Topography -

    https://dl.dropbox.com/s/3edj2v9eeu1k91l/PSP_002532_0935_09_02_07_SL181.1.jpg

    enter image description here

    Posted

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

    I'm enjoying it a lot. Well impressed with your image presentations (he said jealously).

    No other comment at this time - You need a scientist. πŸ˜‰

    Posted

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

    DEM = Digital Elevation Model - two images of HiRISE from different viewing angles and you can use the parallax effect to estimate depths

    Cheers,

    ~Meg

    Posted

  • michaelaye by michaelaye scientist

    Was conferencing last week and now am writing a job application. will reply this week.

    Posted

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

    Thanks Meg. I should have guessed that! Good old parallax. πŸ˜‰ Cheers.

    Michaelaye: Good luck with the job.

    Posted

  • wassock by wassock moderator

    OK time to rake this over again I think. We seem to have a cleft stick held upon the horns of a dilema.

    If the repeating pattern of fans is mostly down to topography then the aims of the project wrt using the directional data from the marking of fans to model wind conditions is flawed if the slope at each fan location is not known and factored in? If this is true why do some fans not follow the slope (without being deformed in the process)?

    If the pattern is not caused by the lay of the land (and are thus down to wind) how does it happen that we get the same sequence of wind directions which are timed to coincide with venting in different places. If this is true how does the wind come back to blow in the right direction so that fans grow along their original axis?

    Posted