Veins on Mars were formed by evaporating ancient lakes

Mineral veins found in Mars's Gale Crater were formed by the evaporation of ancient Martian lakes, a new study has shown.

Sulfate veins prominent at Darwin outcrop veins, observed on sol 402, NavCam NRB_432923862. Field of view 1.3 m. B) 
Garden City image, observed on sol 924, MastCam ML004061. White sulfate veins cut through the surrounding sediments.
 Scale bars are 1m [Credit: NASA]

The research, by Mars Science Laboratory Participating Scientists at The Open University and the University of Leicester, used the Mars Curiosity rover to explore Yellowknife Bay in Gale Crater on Mars, examining the mineralogy of veins that were paths for groundwater in mudstones.

The study suggests that the veins formed as the sediments from the ancient lake were buried, heated to about 50 degrees Celsius and corroded.

Professor John Bridges from the University of Leicester Department of Physics and Astronomy said: "The taste of this Martian groundwater would be rather unpleasant, with about 20 times the content of sulphate and sodium than bottled mineral water for instance!

Drill hole into the John Klein target within Sheepbed Member of Yellowknife Bay, with a light-toned sulfate veinlet visible 
on the back wall. The light-toned veins have been identified as sulfates by ChemCam (Nachon et al. [1]; Schroeder et al. 
[2]) and CheMin (Vaniman et al. [3]). Drill hole is 1.6 cm diameter. Image is white balanced. Scale bar is 2cm 
[Credit: NASA]

"However as Dr Schwenzer from The Open University concludes, some microbes on Earth do like sulphur and iron rich fluids, because they can use those two elements to gain energy. Therefore, for the question of habitability at Gale Crater the taste of the water is very exciting news."

The researchers suggest that evaporation of ancient lakes in the Yellowknife Bay would have led to the formation of silica and sulphate-rich deposits.

Subsequent dissolution by groundwater of these deposits -- which the team predict are present in the Gale Crater sedimentary succession -- led to the formation of pure sulphate veins within the Yellowknife Bay mudstone.

Watchet Bay cliff outcrops on the N. Somerset coast, UK (51°10Ļ59ļN, 3°20Ļ10.7ļW). These outcrops consist 
of Upper Triassic sediments from the Mercia Mudstone Group thought to have formed in a mixed floodplain 
and playa origin environment (Talbot et al. [12]). A) This cliff outcrop contains nodular sulfate and clay mixtures
 toward the base (arrowed) and pure gypsum veins in the mid part of the cliff. Cliff height 30m. Scale bar is 1m. B) 
White gypsum veins derived by partial dissolution of sulfate-rich deposits formed by near-surface evaporation.
SD sandstone dyke, Gy and clay gypsum nodule. Scale bar is 0.5m. C) Pure gypsum veins (some with 
orange coloration) in gray mudstone member of Watchet Triassic mudstone. Scale bar is 0.25m 
[Credit: NASA]

The study predicts the original precipitate was likely gypsum, which dehydrated during the lake's burial.

The team compared the Gale Crater waters with fluids modelled for Martian meteorites shergottites, nakhlites and the ancient meteorite ALH 84001, as well as rocks analysed by the Mars Exploration rovers and with terrestrial ground and surface waters.

The aqueous solution present during sediment alteration associated with mineral vein formation at Gale Crater was found to be high in sodium, potassium and silicon, but had low magnesium, iron and aluminium concentrations and had a near neutral to alkaline pH level.

Light-toned nodules and veins are visible in this image from NASA's Mars rover Curiosity of a patch of sedimentary
 rock called "Knorr." The target is in the "Yellowknife Bay" area of Gale Crater, close to where Curiosity found 
evidence of an ancient environment favorable for microbial life. The rover's Mast Camera (Mastcam) recorded
 this raw image during the 133rd Martian day, or sol, of Curiosity's work on Mars (Dec. 20, 2012). The width
 of the area shown in the image is about 10 inches (25 centimeters) [Credit: NASA/JPL-Caltech/MSSS]

The mudstones with sulphate veins in the Gale Crater were also found to be close in composition to rocks in Watchet Bay in North Devon, highlighting a terrestrial analogue which supports the model of dissolution of a mixed silica and sulphate-rich shallow horizon to form pure sulphate veins.

Ashwin Vasavada, Curiosity Project Scientist from the NASA Jet Propulsion Laboratory said: "These result provide further evidence for the long and varied history of water in Gale Crater. Multiple generations of fluids, each with a unique chemistry, must have been present to account for what we find in the rock record today."

The paper published in Meteoritics & Planetary Science.

Source: University of Leicester [August 05, 2016]