The sensors and science packages that have been deployed on various Mars orbiters have all reported the presence of H2O. The problem is that none of these remote sensors have been sensitive enough to detect the quantity and type of the water. It is now widely accepted that there may be large ice fields, some the size of the state of Arizona, trapped in the Martian crust. We know that the north pole of Mars consists primarily of water ice and that the south pole while primarily constituted of CO2 or "dry ice" also contains a large amount of water. Scientists generally agree that when the Martian atmosphere was stripped away (most likely as a result of the Hellas impact event) much of the available surface water may have retreated underground. When all these factors are considered, the seeps are most likely to have been created by the seeping of liquid water.
Why are the flows wider at the base?
I have read many questions regarding the fan shape of the majority of the flows, and it appears that some individuals are having difficulty understanding the nature of the patterns that have been imaged.
Notice that the origins of the seeps typically start at a fine point and are much wider at the base, but they are also somewhat irregular. This is not only expected, but confirmatory that the phenomenon is most likely liquid rather than fines (loose powdery dust). As the fluid escapes the permeable layer, it begins to saturate the immediate areas of contact. Once the porous surface material has reached saturation, the liquid surface tension of the fluid that is bound to the soil, causes advancement and saturation of adjacent areas of contact. This action is repeated until the fluid stops seeping, or the terminus of the seep reaches a highly porous or permeable surface. In the case of the latter, a more porous material will absorb much greater volumes of liquid. As the seep advances down the slope it will moisten areas directly below it and the regolith/soil that is laterally adjacent. This geometric progression causes the outwardly radiating fan as the seep advances down a slope.
How can we be sure that this isn't darker dust?
As mentioned above, the flow pattern is indicative of fluid (most likely water). But to better understand, and to explain why this is unlikely to be dark dust/fines please see the image below.
While there are images that show slippage and landslide activity, the seep images do not elicit a similar morphology. When dirt, dust, or other material slides down the face of a slope, it will dislodge other material that it comes in contact with, leaving tell-tale signs of disturbance. Moreover, when the slide reaches its terminus, there will be a debris field that is commensurate in volume with the size of the disturbance. We do not find evidence of disturbance or debris in the seep images. To highlight this point, notice that in the image above, a seep that has terminated at the edge of some dunes/crenulations. The seep has made its way around the leading edge of the dune and has left the higher section unaffected. This is precisely what we would expect to find in a seepage of liquid down a slope face. Dirt, dust and other slide materials would likely have covered the tips of these dunes/crenulations.
Why are some of the seeps so light? Are they leaking a different type of material?
In the January image dump by MSSS, not only were a greater number of seep images available (they too are fascinated by the phenomenon and have been specifically targeting areas where the seeps are more abundant), but a new phenomenon was discovered. A white, or bright, seep.
There has been some conjecture about what could cause these bright streaks. I believe there are two possible explanations, both being possible but one being more plausible. One explanation would involve the "super oxidation" that some scientists are now attributing to the Martian soil. When this super oxidized soil comes into contact with fluid there would be a chemical reaction similar to pouring peroxide on dirt. It would be possible under those conditions that the chemical reaction bleaches the soil, leaving a higher albedo signature. The second, and much more likely explanation involves evaporates. Recently there has been vigorous speculation by the scientific community that the near surface water on Mars is brackish (exhibiting a higher degree of salinity). As the fluid charge in the near surface aquifer falls off, the seep will stop and the liquid deposited on the surface will evaporate. The salts and minerals carried by the liquid would then be left behind and would have a higher albedo profile than the surrounding terrain.
Why are the seeps such an important phenomenon?
Liquid water on Mars changes the equation dramatically. If there is near surface liquid water available, the prospects for extant life are radically improved. Moreover, as we look forward to manned missions, the availability of shallow aquifers significantly enhances the potential for mission success.
I believe they could also be melting surface frost or melting permafrost during the warmer temp in Mars's summer months
