Samples of a wide variety of minerals have been collected by NASA's Mars Curiosity rover from rocks in the lowermost layers of Mount Sharp on the Red Planet. The findings point towards alteration in the water environments of the planet over time.
The Mars Curiosity rover had landed near Mount Sharp crater in 2012 and reached the base of the mountain in 2014.
The base of Mount Sharp comprises of layers of rocks which got accumulated as sediments within the ancient lakes over a span of 3.5 billion years. With the help of orbital infrared spectroscopy, it was found that the lowermost layers had variations in minerals, which suggested that changes had occurred in the area.
In a paper recently published in Earth and Planetary Science Letters, scientists with Astromaterials Research and Exploration Science (ARES) Division at NASA's Johnson Space Center in Houston report on the first four samples collected from the lower layers of Mount Sharp.
"We went to Gale Crater to investigate these lower layers of Mount Sharp that have these minerals that precipitated from water and suggest different environments," said Elizabeth Rampe, the first author of the study and a NASA exploration mission scientist at Johnson Space Center.
"These layers were deposited about 3.5 billion years ago, coinciding with a time on Earth when life was beginning to take hold. We think early Mars may have been similar to early Earth, and so these environments might have been habitable."
Four rock samples were drilled near the base of Mount Sharp and the minerals found in them implied that various types of environments were present in the ancient Gale Crater. There is proof about the presence of water with different pH and variable oxidising conditions.
The minerals also show that there were multiple source regions for the rocks in Pahrump Hills and Marias Pass.
Reports on three samples from the Pahrump Hills region have been reported in the paper. According to researchers, it is a rock formation visible on the base of the Mount Sharp's surface, which contains sedimentary rocks that have formed in the presence of water.
Studying such rock layers can yield information about Mars' past habitability, and determining minerals found in the layers of sedimentary rock yields much data about the environment in which they formed. Data collected at Mount Sharp with the Chemistry and Mineralogy (CheMin) instrument on Curiosity showed a wide diversity of minerals.
At the base are minerals from a primitive magma source; they are rich in iron and magnesium, similar to basalts in Hawaii. Moving higher in the section, scientists saw more silica-rich minerals. In the "Telegraph Peak" sample, scientists found minerals similar to quartz. In the "Buckskin" sample, scientists found tridymite. Tridymite is found on Earth, for example, in rocks that formed from partial melting of Earth's crust or in the continental crust -- a strange finding because Mars never had plate tectonics.
In the Confidence Hills and Mojave 2 samples, scientists found clay minerals, which generally form in the presence of liquid water with a near-neutral pH, and therefore could be good indicators of past environments that were conducive to life. The other mineral discovered here was jarosite, a salt that forms in acidic solutions. The jarosite finding indicates that there were acidic fluids at some point in time in this region.
There are different iron-oxide minerals in the samples as well. Hematite was found near the base; only magnetite was found at the top. Hematite contains oxidised iron, whereas magnetite contains both oxidised and reduced forms of iron. The type of iron-oxide mineral present may tell scientists about the oxidation potential of the ancient waters.
The authors discuss two hypotheses to explain this mineralogical diversity. The lake waters themselves at the base were oxidising, so either there was more oxygen in the atmosphere or other factors encouraged oxidation. Another hypothesis -- the one put forward in the paper -- is that later-stage fluids arose.
After the rock sediments were deposited, some acidic, oxidising groundwater moved into the area, leading to precipitation of the jarosite and hematite. In this scenario, the environmental conditions present in the lake and in later groundwater were quite different, but both offered liquid water and a chemical diversity that could have been exploited by microbial life.
"We have all this evidence that Mars was once really wet but now is dry and cold," Rampe said.
"Today, much of the water is locked up in the poles and in the ground at high latitudes as ice. We think that the rocks Curiosity has studied reveal ancient environmental changes that occurred as Mars started to lose its atmosphere and water was lost to space," Rampe added.
In the paper, the authors discuss whether this specific area on Mars is a mark of this event happening or just a natural drying of this area. Scientists will search for answers to these questions as the rover moves up the mountain.