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In my new model, all the material that we see transported into the northern plains of Mars has been moved by vapor-supported flows. Cold (Cryogenic) flows of rock, dust, and CO2 Vapor, plus a passive cargo of water-ice and degrading clathrate would have poured along the channels, raising a huge cloud of dust - a truly global dust storm. Along the way, the larger rocks are dropped, often leaning against each other in inclined rows, like shingled roof tiles. This is exactly what was seen at the Pathfinder Landing site. Those dents and scars on the boulders were caused by the rocks banging together in the cold dry flow, not underwater. Indeed, the rounding of the boulders, often cited as evidence of a water flow is merely evidence of a fluid flow in general, and a cold density flow is much easier to arrange on Mars than a water flood.

By the time the northern plains are reached, mostly fine debris remains and this spreads out and settles down as a wide thin blanket, filling hollows, smoothing out the topography and mimicking the bed of an ocean (on Earth, the ocean floors are smooth not because of waves in the water smoothing out their beds, but because submarine density flows do the same job of filling hollows and smoothing out peaks).

The recent Malin and Edgett flows are also more likely to be small scale seeps and outbursts of liquid CO2, than liquid water. Although most of the liquid CO2 has escaped from the regolith by now, some remains in cool sheltered spots, on poleward facing slopes. When our rovers explore these areas we should anticipate signs of chemical alteration by CO2, not by H2O!

Other channels on Mars
The outburst flood channels on Mars are relatively young. Formed during the Late Hesperian and Early Amazonian (~ 1 to 2.5 billion years ago), they are relatively fresh and undisturbed except for small meteorite craters and sand dunes. Other older types of valleys and channels exist that may have had different formation mechanisms.

In the earliest times of which we have evidence - the Noachian (over 4 billion years ago), there are rather different valleys. These form dendritic networks and are associated with drainage around major impact craters. Although they look superficially like branching river and stream systems on Earth, they lack the fine detail of sub-branches and have blunt tips to the valleys. In part this may be because they are so old and worn down, but the differences seem real. Fluids seem to have been widespread in the regolith at this time - at least in local areas, and to have been seeping out into the drainage network, sapping away (undermining) the valley heads. Over time, an initial small channel would grow into a branching network.

We know very little about surface conditions during the Noachian. Certainly, major planetary bombardment was still continuing and the atmosphere of this Early Mars might either have been significantly warmed by the impacts, or cooled by dust and clouds in an "impact winter" scenario. It may be best to leave the Noachian aside for now - it clearly needs much more research, and it is easier to work back in time gradually. Let's work on understanding the middle age of Mars, before we go back to its earliest times.

Another example often proposed as evidence for the steady flow of rivers on Mars are the sinuous valleys of Nanedi and Nirgal Valles. On Earth, sinuous valleys equate with meandering rivers, so perhaps the same is true for Mars? Unfortunately this analogy doesn't hold water. On the seabeds of Earth are numerous meandering channels formed by subsea density flows (submarine turbidity currents, or turbidites). These are formed not by steady flow of fluid but by repeated short bursts of density flows down the meandering channels. Although they look identical to subaerial channels formed by sluggish rivers on Earth, they were formed on the modern seabed, many kilometres down, and are still active today.

Unfortunately for both the water-on-Mars adherents, and for my own model, the gross morphology of channels is not clearly diagnostic as to the type of fluid that formed them. For all of the examples discussed, any process chosen from subaerial flows of water, volcanic outbursts, submarine turbidites, or CO2 vapour-supported flows is equally capable of producing the evidence we see. As scientists, we must examine the other evidence and decide which process is most likely. If we see volcanic cones in the source areas, then we would invoke pyroclastic flows. If we see that everything is taking place within an ocean, then we would assume turbidites.

On Mars, we see neither of these. There aren't any particular volcanic features in the chaos zones. The evidence for a northern ocean on Mars is already weak and certainly doesn't permit it to extend this far into the higher ground source areas of the flows. Sometimes channels are found on the flanks of volcanoes, but this association seems to be telling us that volcanic-sourced volatiles are forming the fluids in the flows, secondary to the eruptions that built the volcanoes.

The decision about whether liquid water or CO2 vapour is the active fluid has to rely on the other evidence we have from Mars. We know that modern Mars is cold and dry. We know that we have difficulty explaining much of the surface evidence of Mars if we assume it was previously warm and wet. We observe, interestingly, that a CO2 -based explanation of the channel features on Mars solves all of the existing paradoxes and actually helps explain a lot of the minor niggling details about Mars that don't quite add up.

If we accept the CO2 -based model, then there is no carbonate on Mars because there never was a "warm and wet" episode. No water means no aqueous chemistry so no carbonates (and no surface life). The Faint Young Sun Paradox is now an integral part of this model. Early Mars was even colder and drier than it is today, with less than 1 millibar of atmospheric pressure. The volumetric problem with the outburst "floods" is easily solved. When liquid CO2 explodes from underground, it expands by hundreds to thousands of times, so the spaces between the grains can easily hold enough CO2 to transport the entire debris load all the way to the northern plains.

The result of this objective analysis is a strong suspicion about the standard model of Mars, and the need to do more work on White Mars models to test how well they fit the data, and what predictive power they have about Mars. This may be in terms of surface mineralogy, details of channel morphology, or the chemistry of the surface and regolith.

White Mars Part Four

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