Scientists use salts to determine how old water is on Mars

Ellen Liske and Bethany Elmann of the California Institute of Technology have drawn up a clearer picture of Mars' past, figuring out the likely behaviour of the last liquid water on Mars and determining when it stopped flowing, all by tracing salt deposits.

They examined traces of chlorides, as they are the salts most readily soluble in water. Therefore, if there is water around, these chloride salts will be dissolved in it. Thus, the researchers mapped the presence of chloride deposits across the Martian surface. By analysing these sediments, the researchers obtained a number of data about the water that brought them there.

The scientists found that many of these sediments were in relatively narrow channels and that the height of the deposits was often higher than that of neighbouring basins. Lisk and Elmann suggested that water flowed into the channels but dried out before reaching the basins they filled. Another factor the researchers found is that these channels were relatively narrow and shallow - less than three meters deep.

In addition, the researchers looked at the age of the salt deposits. They focused on the dates of bedrock deposits which give the maximum age for the salt deposited on top of them. Their data range from 3.3 billion years ago to 2.3 billion years ago, much later than previously thought.