Water at Mars?

An Overview

To find evidence water had existed at Mars -hinting to past (or current) life- was the target of the Twin Rovers. As of spring 2007, as both the rovers have been working during a whole three year at Mars, it seems well that the sediments at Mars are mostly due to volcanism, and not to oceans like the case at Earth. The water-related activity which has been seen at Meridiani Planum, on the one hand, and at Gusev Crater, on the other hand, are of the type, in one case, of a large ocean or sea, and, in the other, of an explosive, volcanic activity leading to the formation of 2-yard high layers of basaltic rocks. The large ocean, or sea, at Meridiani Planum, further, likely alternated with periods of mere 'playas' (or 'salt flats), as the explosive basaltic activity at Gusev was due to that basalt lava entered into contact with brine reservoirs Another major discovery is that the water involved in the processes found by the mission is of a salty nature. This may have proven a challenge to life conditions at Mars, albeit that is not necessarily unsurpassable. The sedimential nature of the rocks found by both Spirit and Opportunity, on the other hand, leaves that feeling that they might be the ideal place for fossils. All such water-related environments are billions of years old. Some other places looks like less salty as rocks might have formed from water dissolving minerals out of volcanic rocks

By March 2015, the question of water at both landing sites establishes itself like the question of that there was either acidic (or salty) water, or water really favourable to life

An Important Sea At Meridiani Planum Looks Like Possible

It's at Meridiani Planum plains that a Martian water-related history is the most plausible. Water there was acidic groundwater that sometimes reached the surface and evaporated away, leaving salts behind. Opportunity, first, had the extraordinary luck to land just inside a shallow crater where sedimentary rocks were seen and of easy examination. As such layers were hinting to some salt flats (or "playas") alternating dry periods and two inches (5 cm) or much deeper of water flowing, Opportunity then moved to a nearby large crater dubbed "Endurance Crater" providing access to much deeper rock layers. The same process than at the landing crater was found at work but it was seen occurring down to the deepest of the crater. This might fit well with observations from orbit which are showing that Meridiani Planum is featuring thick stacks of rock layers. Meridiani Planum might really have been the place of an ocean or of a vast sea on one hand, with periods of salt flats on the other hand. This does not exclude however the fact that, even at deep layers, layering mechanism might be explained by volcanic material being re-processed by water and/or wind. The following, large crater which was explored then by Opportunity -the Victoria Crater- gave access to deeper layers still. That confirmed that the Meridiani Planum plains had really been shaped by water and that, further, the region had featured dunes. Those large impact craters, thus, fractured the sedimentary layers which had been formed due to water in the region. The following target of the rover, now, is a larger crater still, the Endeavour Crater. That crater, further, is older than the previous ones and will give access to geological strates which predate the water-born sediments of Meridiani Planum. That likely will allow to supplement the vision, from a geological point of view, of that region of Mars

The studies performed by Opportunity at the large Victoria Crater are helping to a better understanding of what occurred there billions of years ago! It looks like there was a lot of acidic water, coming and leaving over timespans and interaction with volcanic rocks. That produced sulfate salts and sand rich in that material. Wind then came and blew that sand into dunes. New watery episodes solified that dunes into sandstone as further alteration by water produced the iron-rich spherules from the sandstone, mineral changes and angular pores left when crystals dissolved away. The spherules in rocks deeper in the crater are larger than those in overlying layers, suggesting the action of groundwater was more intense at greater depth. Spherules up to about one-eighth inch (3 millimeters) in diameter found in Gale Crater by rover Curiosity in 2013 do not have the iron-rich composition of Opportunity's. The windy activities still shape the landscape today like for example, reducing the size of the impact Martian craters. The Victoria Crater, for example, was blasted by a space rock like a a hole about 2,000-ft (600-m) wide and 400-ft (125-m)) deep. Wind erosion widened it gradually, chewing at the edges and partially refilling it, increasing the diameter by about 25 percent and reducing the depth by about 40 percent. The lower layers showed less sulfur and iron, more aluminum and silicon matching what had been found at the smaller Endurance Crater

At Endeavour Crater then, scientists found gypsum veins and a rich concentration of clay minerals hinting about water chemistry that was neutral, instead of acidic thus more favorable for microbial life

A Volcanic Water History at Gusev Crater Only?

The history at Gusev Crater is different and is likely volcanism-related with evidence of a ancient Mars that was a hot, wet, violent place, with volcanic explosions, hydrothermal activity, and steam vents. In the intercrater plains, Spirit however found hollows where a possible swelling-shrinking brine process is involving underlying water percolating at the surface, with a salty soil. As far as volcanism is concerned, Spirit found, in the plains, rocks which seemed to have been volcanism-interacted, as, along the slopes of the Columbia Hills it found varying marks of water-related processes, that is mostly layered rocks. The studies were mostly undecisive still, as the slope was matching the angle of the hills's layers. It's not further into the slope that Spirit eventually found, by May 2005, real, large, layered outcrops. The first results of their studies are showing that all of them are the result of the accretion of explosive material, likely the result of strong and repetitive volcanic eruptions at Gusev Crater with ash and debris settling down in different ways, then altered by water, as water was then found in large quantities in the crater. This fits well with what Spirit had already seen along the slopes, when volcanic material re-accreted with water involved was one of the hypothesis. So it might that the rocky formation inside Gusev are due to a strong, time-stretched volcanic activity in the region, with large quantities of water present all along this period

Latest examination of data collected in 2005 by Spirit in the Columbia Hills reveals high concentrations of carbonate, which originates in wet, near-neutral conditions, but dissolves in acid. The ancient water indicated by this find was not acidic. NASA's rovers have found other evidence of formerly wet Martian environments. However the data for those environments indicate conditions that may have been acidic. In other cases, the conditions were definitely acidic, and therefore less favorable as habitats for life. The find is showing that that conditions that could have been quite favorable for life were present at one time in one place. Massive carbonate deposits on Mars have been sought for years without much success. Numerous channels apparently carved by flows of liquid water on ancient Mars suggest the planet was formerly warmer, thanks to greenhouse warming from a thicker atmosphere than exists now. The ancient, dense Martian atmosphere was probably rich in carbon dioxide, because that gas makes up nearly all the modern, very thin atmosphere. It is important to determine where most of the carbon dioxide went. Some theorize it departed to space. Others hypothesize that it left the atmosphere by the mixing of carbon dioxide with water under conditions that led to forming carbonate minerals. Expectations in the 1990s were that carbonate would be abundant on Mars. However, mineral-mapping spectrometers on orbiters since then have found evidence of localized carbonate deposits in only one area, plus small amounts distributed globally in Martian dust. By 2010 water, as snow melt, was also found atop the Columbia Hills to have trickled into the subsurface fairly recently and on a continuing basis with thin films of water may have entered the ground from frost or snow during cyclical climate change and carrying soluble minerals deeper than less soluble ones. The relatively insoluble minerals near the surface include what is thought to be hematite, silica and gypsum. Ferric sulfates, which are more soluble, appear to have been dissolved and carried down by water.The surface keeps being covered by wind-blown sand and dust

When dragging its inoperable right-front wheel rover Spirit plowed up in 2007 bright white soil in the Columbia Hills. That was nearly pure silica, which shows that there were once hot springs or steam vents at the Spirit site, which also could have provided favorable conditions for microbial life. The silica-rich soil neighbors a low plateau called Home Plate. The investigations at Gusev site thus are hinting to a different image of early Mars, like a violent place, with water and hot rock interacting to make spectacular volcanic explosions!