The enigma that is the ongoing search for water on Mars just keeps getting stranger. In the four and a half years NASA’s Curiosity rover has been exploring the surface of the Red Planet, scores of chemical and geological evidence have been discovered indicating that water likely once flowed on Mars. However, conflicting evidence has been found concerning when exactly in Martian history this water existed. Some evidence points to Mars being dry for millions of years, while other data suggests the date of Mars’ drying up could be billions of years ago.
Just this week, a new report issued by NASA has done little to help unravel this mystery but has instead complicated the Mars water riddle even further. According to a NASA/JPL press release, samples of Martian rock indicate that the planet did not have enough carbon dioxide in its atmosphere 3.5 billion years ago to melt ice into liquid water. That discrepancy means that the leading theory about when Mars could have once been wet has gone right out the window - along with decades of data confirming that theory.
NASA’s recent announcement comes on the heels of Curiosity rover’s analysis of rocks found a dry lake bed in Mars’ Gale crater, previously thought to be a former body of liquid water on Mars. As water dries and evaporates, aqueous carbon dioxide molecules react with other minerals to form carbonates which can be used by geologists to date the evaporation of ancient bodies of water. NASA's Thomas Bristow analyzed Curiosity’s recent Gale crater data for the presence of carbonates and, like many of his colleagues, is dumbfounded by the contradictions in the chemical analyses of the Martian lakebed rocks:
We've been particularly struck with the absence of carbonate minerals in sedimentary rock the rover has examined. It would be really hard to get liquid water even if there were a hundred times more carbon dioxide in the atmosphere than what the mineral evidence in the rock tells us. [...] The Curiosity results bring the paradox to a focus. This is the first time we've checked for carbonates on the ground in a rock we know formed from sediments deposited under water.
One theory for the absence of carbonate minerals is that perhaps this lakebed was a body of some other liquid other than water which was covered by liquid ice. However, a frozen lake would have left telltale geological formations that just aren’t present in the dry Gale crater lake. While no other possible theories have been offered in the Curiosity researchers’ recent publication, the study adds that new theories about water cycles and behavior on other planets must now be proposed.