Salty waters on Mars could host Earth-like life
Mars is an unlikely place for life as we know it to thrive. The surface is bombarded by DNA-damaging radiation. Water has only been confirmed on the frigid landscape in the form of ice and hydrated minerals. And there's barely even a wisp of oxygen in its paltry atmosphere.
But the case for life on the red planet just got a little stronger with a new study that suggests salty waters thought to potentially exist near the surface could hold enough dissolved oxygen to support familiar forms of microbial life. In some special cases, there would even be enough of the element to harbor basic oxygen-loving animals like sponges.
This certainly doesn't mean there is life on Mars—scientists aren't even sure if liquid water flows on or near its surface. However, the surprising research, published today in Nature Geoscience, hints that perhaps the modern Mars environment is not quite as inhospitable as we once thought.
“That's the thing of habitability; we never thought that environment could have that much oxygen,” says the study's lead author Vlada Stamenković, a planetary scientist and physicist at NASA's Jet Propulsion Laboratory. “It completely changes our understanding of the potential for life on current-day Mars.”
The manganese mystery
The thin atmosphere that blankets the red Martian landscape is mostly made of carbon dioxide, with traces of nitrogen and argon gas. Measurements from rovers and orbiting spacecraft suggest that a mere 0.145 percent of the air is oxygen, which thought to be released as sunlight breaks apart some of the carbon dioxide molecules.
Although this is a pitifully low amount of oxygen compared to the nearly 21 percent in modern Earth's atmosphere, there are hints something strange has been going on with the life-giving gas on the red planet.
In 2014, researchers were excited to discover manganese oxide on Mars' surface. Manganese is tough to oxidize, and unlike the oxidized iron that gives the rusty red planet its signature look, forming manganese oxide requires the presence of either oxygen or microbes, explains Kirsten Siebach, a planetary geologist at Rice University who was not involved in the work.
Researchers have previously suggested that this compound points to an ancient Martian atmosphere flush with oxygen. But Stamenković and his colleagues thought there just might be another way.
With an average surface temperature of -81 degrees Fahrenheit, Mars doesn't readily sport vast flows of liquid water. To date, there are no confirmed discoveries of Martian puddles—only hints of water deep underground. But scientists believe that water might exist near the surface as a brine, which is essentially very salty water.
When you add salts to water, it slightly lowers the point at which the water freezes. So the addition of salts to Martian ice—including the magnesium and calcium perchlorate salts widespread in Martian dust—will let that frozen water turn fluid.
But then salts pose another problem: The more salt that's present, the less oxygen the water can hold. At the same time, the colder the water, the more oxygen it can dissolve. It's a game of oxygen tug-of-war, with salts pushing out the dissolved gas and the cold temperatures pulling it in. To figure out which effect might win, the researchers turned to mathematical modeling.