The dark brown areas are salts containing trapped water. These water bearing streaks extend down slope every summer, which is powerful evidence of flowing water, then cease moving as Martian winter approaches. The iridescent blue is produced by the mineral pyroxene a mineral common in lava rock on earth, the moon and Mars. The chemical potential between the highly oxidizing water bearing salts and ferrous iron from the mineral pyroxene could provide energy for the subsistence of bacterial life forms if they ever evolved on Mars.
Powerful evidence of actively flowing water on Mars has been discovered by Georgia Tech and NASA/JPL scientists. Trapped water has been identified in the spectral signature of dark salty streaks called linae that form and extend downhill in intricate braided flow patterns on steep slopes every Martian summer, by a team led by Georgia Tech scientist Lujendra Ojha. Bleach-like magnesium chlorate and perchlorate salts pull vapor our of the air and out of the soil forming brine, leaving dark immobile surface crusts as Martian winter approaches. The researchers do not know the exact source of the water. These hygroscopic salts could be taking up water vapor from the Martian summer air or could be taking up vapor that flows upwards in the soil in Martian summer. Martian soils and subsoils are very likely partially saturated with brines. The same types of vapor transport processes that take place in cold desert soils on earth may be taking place on Mars with the caveat that the chemistry is much more oxidizing on Mars.
Dark streaks show where salty water has flowed on Mars, leaving a hydrated solid salt of a bleach like compound that stabilizes liquid water in Mars' harsh, cold, dry, environment.
Mars was much warmer in wetter in the first billion years of its history before it lost literally an ocean of water to space. Because Mars does not have a magnetic field like earth, lacks an ozone layer and has a much smaller mass than earth, the solar wind and ultraviolet radiation have stripped off almost all of its water and its former atmosphere. Extreme enrichment of heavy hydrogen to light hydrogen has been measured in Mars' remaining water. Because the Martian water initially had the same mixture of heavy to light hydrogen as most water and ice across our solar system, scientists have been able to calculate that Mars once had enough water to form an ocean. Primitive life could possibly have evolved in that ocean. As the ocean was slowly stripped away that life could have retreated to the subsurface and survived in soil brines which stayed liquid despite the severe cooling that took place when Mars lost almost all of its atmosphere to the solar wind.
A streaked Martian crater wall shows where salty water flowed recently in Martian summer, leaving a salty dark crust when flow ceased as Martian winter came.
On earth, a variety of primitive extremophiles are found in very cold brines found in the Canadian Arctic on Axel Heiberg island. Although the chemistry on Mars is far more oxidizing that the chemistry of these cold brines on earth, the adaptation of life to these extremely cold and salty conditions on earth has given scientists hope that life might survive in cold Martian brines.
Cryoenvironments are defined as permanently subzero or frozen environments, such as permafrost, glaciers, ice sheets, multiyear sea ice, high-elevation Antarctic dry valleys, and some cold saline springs (1–6). Microorganisms inhabiting cryoenvironments must face the challenges of subzero temperatures, low water activity, and, often, high solute concentrations to sustain their viability. The cold saline springs on Axel Heiberg Island (AHI) in the Canadian high Arctic discharge through 500 to 600 m of thick permafrost, maintain a liquid state at subzero temperatures, and offer a unique opportunity to assess microbial adaptations to extremes of both high salinity and subzero temperatures (3, 4, 7–9). These springs occur in an area with an average annual air temperature of −15°C, reaching below −40°C during the winter months, and probably originate from subpermafrost groundwater flow through carboniferous evaporites in areas of diapiric uplift on AHI (10, 11). Other Arctic cold springs, on Ellesmere Island in the Canadian high Arctic and on the Norwegian high-Arctic Svalbard archipelago, have been reported (12–14), although the discharges from these springs are not subzero. Viable microbial communities have been described for all of these Arctic springs (3, 4, 7, 8, 13–15).
Wired magazine has an excellent post on the news about flowing water on Mars.
Ojha and his team have watched these lineae form every Martian summer, growing wider week after week until they slowly fade come winter—exactly the times and places where conditions are right for liquid water to exist on Mars. Plus, the surface is crusted with salt, which could help stabilize liquid water so it doesn’t boil or freeze.
Ojha notes that they haven’t actually observed water flowing on Mars. The team took their data from the CRISM instrument on the Mars Reconnaisance Orbiter, which, frustratingly, only observes the surface every day at 3 pm. That’s when Mars is at its hottest and driest, so any liquid water oozing on the surface would have long since evaporated by the time MRO laid eyes on it.
Still, the water left a distinctive chemical trace. “Whatever is flowing on Mars is hydrating the salt,” Ojha says, “and we’re seeing that hydration in the spectral signature.” After extracting spectral information from pixels of the CRISM instrument’s data, Ojha and his team determined that the salts—magnesium perchlorate, magnesium chlorate, and sodium perchlorate—had water molecules interspersed in their crystal structures. That’s pretty strong evidence that they were deposited by flowing water.
Please see Wee Mama's Dailykos breaking news diary on Mars' water
here.
In my personal experience this water on Mars is similar to water found in uranium tailings piles in the western U.S. where highly oxidizing "water-loving" salts produced by ore processing stay wet under dry desert conditions. Bacteria are able to thrive in this harsh earth environment by exploiting the energy involved in the differences in chemical potentials between the highly oxidized tailings and the less oxidized natural materials. Similar chemical potentials are present on Mars. On Mars the bleach-like magnesium perchlorate salts are produced by reactions triggered by UV radiation that strikes the Martian surface in the absence of an ozone layer in the modern Martian atmosphere. Below the surface the soil and rock is likely less oxidized. Thus there is an energy source that could support bacteria below the surface of Mars.