The indefatigable quest for firm evidence of liquid water on ancient Mars appears to have finally succeeded. NASA's Opportunity rover recently discovered a dozen bright veins of gypsum mineral and the results were presented at a meeting of the American Geophysical Union in San Francisco, California. The rover used an array of instruments to confirm the chemical composition of the veins as calcium sulphate. Since calcium sulphate can exist in different forms depending on the amount of water it contains, the presence of gypsum, a hydrated mineral of calcium sulphate, strongly suggests the presence of water. Although gypsum has been found on far northern locations on Mars, what makes the latest find particularly significant is its presence at the very point where it was formed. This will help scientists understand the paleoenvironmental conditions on the red planet. The veins, which are 1 cm to 2 cm in width and 40 cm to 50 cm in length, are located at the edge of the Endeavour crater where the sulphate-rich sedimentary bedrock meets the volcanic bedrock that lies exposed at the rim of the crater. Scientists speculate that gypsum got precipitated when water containing calcium sulphate flowed through fractures.
Our current understanding is that water is a key resource for life to exist. Hence scientists searching for life on Mars or other planets look out for signs of liquid water. However, the mere presence of water does not necessarily mean micro-organisms exist. Salinity, acidity, and temperature play a predominant role in determining habitability in water bodies on Earth. Extrapolating from this, the data sent by rovers from other locations over the years have revealed a very harsh environment for life to exist. Even the Meridiani Planum region located in the Martian equator, which was considered to have the least harsh environment, turned out to be inimical to life because of its high acidic conditions. Unlike other locations explored so far, the edge of the Endeavour crater does not have any jarosite (an iron sulphate mineral) deposit indicative of acidic conditions. The combination of gypsum veins and the absence of jarosite probably indicates a “possibility of water being more neutral,” which basically means a less inhospitable environment. Whether ancient Mars was habitable or not, the discovery of gypsum reveals that liquid water was once present. The recent discovery of clay minerals, which were found to be widespread in the planet's Noachian terrain, supports the same idea. After all, clay minerals arise after a long-duration interaction between water and rocks.