MARTIAN SPIDERS: CHANGES OVER TWO MARTIAN YEARS, G. M. Orme¹ and P. K. Ness².

Introduction:  Images of Martian spiders have now been released over two full Martian years. This makes it possible to compare many of the same formations with the first year [1].

Seasonality: A total of 267 active or changing spider images were selected [2] [3] that extended over two Martian years. Active spiders were found to mainly be around Chasma Australe.

These images were arranged in order of Solar Longitude with the two years combined in one sequence of images. Spiders begin to appear in spring and dissipate in autumn. Some spiders had been reimaged from the previous year, and this allowed a direct comparison of the changes in them.

The evidence seems clear that in active areas spiders change seasonally. In early spring they are seen as small but as the summer progresses in some areas they explode in numbers. As autumn approaches the spider branches are seen to progressively shrink and degenerate. Eventually most disappear completely, falling apart and merging into the soil. E0700758, E0800043, M0900157,  E0801158, and M0900528 are examples of spiders growing. M1104046,  M1200543, and E1200911 shows spiders dissipating in late summer.

This growth seems generally unrelated to the temperature of sublimating CO2. Available temperature data [4] connects the main period of spider growth to around -60C and above at Ls 250 but the temperatures seem to increase until Ls 300 which is around the time of maximum spider growth.  This is consistent with melting brines [5] not CO2. Chasma Australe is one of the warmest parts of the pole in summer. Because the temperature data is an average, with dark soil some areas with spider growth may be warmer than this. The South Pole at this time has more even temperatures because the sun doesn’t set at night.

A transparent CO2 covering [6] should have sublimated well before the main period of spider growth. In the early stages of growth wind associated with CO2 sublimation forms streaks near many spiders such as in E0800043 but the wind has ceased well before most growth occurs. This indicates CO2 has already sublimated in the area.

This growth and decline is difficult to account for geologically. While models can be constructed to partially explain growing spiders, this same material then has to dissipate even sublimate leaving virtually no trace while the temperature is going down in autumn. A reverse chemical reaction should not be occurring with lowering temperatures.

The spiders generally start with a pale albedo though most of the streaks are dark, for example in M0906428, E0901155, and M1000071. These streaks don’t change the spider albedo even though streaks often go right over the spiders. This would imply perhaps a form of CO2 or water ice making the branches but the temperature rules out CO2 and later falling temperatures then cannot be associated with sublimating the CO2 and dissipating the branches after the spiders have lasted through the hotter summer. As they start to decline the spider albedo becomes more like the soil around them for example M1003666,  M1100222 , M1100396 , M1101739, M1102393, and M1104046. When branches dissipate the remains are usually not even visible as a different albedo.

A chemical reaction then must come from this soil, create a pale albedo chemically, grow when CO2 is sublimating, and then shrink when CO2 is returning, to change back into the same albedo again.

Known materials: All of the candidate materials spiders could be made of are seen elsewhere on the pole, but are not spider like. Spiders are unlikely to be dunes because there are dune and streak shapes that look nothing like spiders, and they are found in areas with the same temperatures.

      CO2 of course is widely seen on the pole and in no other case forms anything like spiders. No chemical process on Earth is known that would make CO2 form long branches. The most difficult argument to overcome is probably the North Pole where virtually identical conditions occur, except the temperatures are cooler through the summer. If spiders are made from CO2 or any material interacting with it then we should see spiders there. So far not one single spider has been observed on the North Pole.

      This implies that whatever is on the South Pole and making spiders is not on the North Pole. The only difference seems to be temperature, so the most likely reason is spiders need the extra heat to form. Dust storms should distribute the same minerals to both poles and it seems hard to believe there are minerals in the south that are totally non existent in the north.

Surface shape:  While inactive spider areas may contain ravines active spiders are invariably above ground not below.  Models based on dendritic drainage systems don’t explain how these shapes can form above ground and much higher than the ravines. As spiders dissipate they fade into the soil and in most places there is no ravine at all left by them.

This is difficult to reconcile with a fluid formation as like a river bursting its banks spider branches should not be able to meander across a terrain without banks to hold the fluids in.  These branches seem to be even 10 meters tall according to shadows, and it is impossible for fluids to move like this without pooling. The upper surface of branches seems to be usually rounded, which is not reconcilable with the top of a fluid which should be flat.

Against gravity: Spiders form patterns that are very similar to each other regardless of the terrain. In thousands of cases spiders are seen on slopes yet the branches point uphill just as much as downhill. It is impossible for a fluid or dune to form a shape like this against gravity, all the branches should point downhill. For example all known water gullies on Mars point downhill not uphill. All known ancient river branches on Mars follow gravity, none move against gravity as if they once flowed uphill.

      In countless examples spider branches instead of going around small hills go right over the top of them. When encountering depressions they either avoid them or go along the rim with no regard for gravity. Spider branches often point towards each other and if they were following a slope they should connect and perhaps form a pool but they never do.

       In E1201762 spider branches almost never cross though any fluid should tend to pool. Many branches from different spiders point at each other but none join. In many cases here branches climb over small hills completely against gravity. Branches typically have very similar angles, but dendritic patterns should vary randomly as the terrain is usually very uneven. In each case the branch is moving against gravity. In E1004220, E1102247, and E1200329 there are perhaps thousands of places where branches move against gravity.

      Active Spider shapes are completely different to cracks [7]. Any material that cracks would also tend to follow gravity; so on a slope there should be an asymmetry between the cracks going uphill and downhill. The material cracking itself has weight and so should crack unevenly under gravity on a slope. Spiders are above ground and cracks are below ground. If material forms in the cracks then it too should follow gravity and pool outside the cracks sometimes, but never does.

Fibonacci branching: This was noticed in the first Martian summer and has become even more obvious. In many spiders virtually every single branch follows a mathematical relationship called Fibonacci branching. Also on a spider the angles between the branches are usually very similar regardless of the slope or terrain and this is a feature of Fibonacci branching. This can be seen in a spider formation reimaged 3 times, as M0902042, E1201762, and E1301971.

E0800043 , M0900157, M0900528, E0801158 , M0806244 , M0901352 , M0901567, M0903082, E1003496, M1102393 also contain clear Fibonacci branching.

      So far on Earth there has never been an example of geological formations based on Fibonacci branching.

Types: The mystery of the spider’s formation is compounded by there being distinct types, found in different terrain. Some form large clusters and strongly resemble the “Swiss Cheese” formations, and so may be related to them. They are found at the opposite side of the pole to the “Swiss Cheese” for example M1000935 ,  M1003277, M1100580, M1101351, and M1101643.

It may be the “Swiss Cheese” areas are currently inactive spider areas. The texture around them, referred to as “elephant hide” by Byrne [8] is very similar to spider branches.

Debris: Any kind of geological formation should leave debris after it dissipates, but spiders rarely do. If material is to flow from the central core it should in some cases form a pool rather than branches, but spiders never do. If material is to flow along the branches to form them then it needs to be confined somehow to avoid pooling but in most cases there are no ravines and the spiders are much higher than the ground. If this material is to travel at speed to get up hills against gravity then it should not be able to suddenly slow down to turn to make a branch and then speed up again to make more branches uphill. Some spiders can make 10 or more forks going uphill. Some material should be at the end of channels in their formations like we see at the end of gullies and deltas but the spiders leave no residue build up at the ends of their branches. For example the gullies in M0306110, M0302290 and M1302043 have debris at their ends unlike spiders.

References: [1] Orme G. and Ness P. K. (2002) Journal of the British Interplanetary Society, 8 February 2002. Vol 55 No 3/4, March-April Edition, Pp 85-108. [2] Orme. G. M. and Ness P. K. (2003) New Frontiers in Science available online at http://www.newfrontiersinscience.com/ Members/v02n03/a/NFS0203a.shtml [July 14th 2003] [3] Thomas D. J. (2003) Marsbugs Volume 10 Number 23 9 June 2003. [4] Titus T. N. (2003) South Polar Cap Recession available online at http://www.mars-ice.org/spole99.html [July 13th 2003]. [5] Burt D. M. et al. (2002) Lunar and Planetary Science XXXIII 1240.pdf  [6] Kieffer H. H. (2003) Sixth International Conference on Mars 3158.pdf  [7] Kieffer H. H. (2000) Mars Polar Science 2000 4095.pdf  [8] Byrne et al. (2003) Lunar and Planetary Science XXXIV 3112.pdf