Follow the water is NASA’s mantra for Mars exploration. Water is a key ingredient for life. So missions to the Red Planet have sought out regions that show evidence of water, either past or present. Such regions should be the most likely to hold evidence of life.

But some scientists think the search ought to be expanded. Don’t just follow the water – follow the salt.

The Viking landers of the 1970s carried several experiments to look for microscopic life. They fed a bit of Martian dirt into small chemical laboratories. The experiments added water, nutrients, or other ingredients. They then looked for gases or radioactive elements that might be produced by such organisms.

A couple of the experiments found just what they were looking for. But most scientists later decided that the evidence was produced by chemical reactions. Others maintained that they really were produced by life.

A recent paper argued that the composition of the soil at the landing sites was very salty. On Earth, some organisms live in such conditions. They draw their water from the salts. But if you add water, they die. So the Viking landers might have found life – then killed it off. So NASA might need to expand the search – by following the salt.

Mars is especially easy to see tonight. It’s right next to the Moon at nightfall, and looks like a bright orange star. They’ll be a little farther apart as they set, in the wee hours of the morning.

Script by Damond Benningfield