A study published in the journal Nature Geoscience suggests that salty water buried just below the Martian surface might have enough dissolved oxygen to support life like microbes, and perhaps even simple animal life, like sponges.
This surprising conclusion could help reframe scientists’ understanding of the habitability of the Red Planet, both past and present, the authors write.
“We are living in exciting times,” said lead author Vlada Stamenkovic, a research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “Given that much more work is still needed to better understand Martian habitability, I hope this will generate enthusiasm in the scientific community , around the world, to think of Mars as a potential place for life to exist, even today.”
The key to groundwater
Water flowed generously through the red earth of Mars in the past , as observations made by spacecraft such as NASA’s Viking orbiters, the Mars Reconnaissance Orbiter, and the Curiosity, Spirit, and Opportunity rovers have shown. In fact, many scientists believe that the red planet even featured oceans billions of years ago.
However, surface water disappeared a long time ago, after Mars lost most of its atmosphere and became the cold, dry world we know today. But the researchers believe that moisture persists underground, both in deeply buried aquifers and in pockets of brine (which may be just below the surface).
The scientists modeled the oxygen storage potential of near-surface brine reservoirs, calculating how much dissolved O2 (oxygen) they could hold at various locations around the Martian globe. This is an interesting approach, since life as we know it does not necessarily need oxygen : the first organisms on Earth were anaerobic (they do not use oxygen in their metabolism), as is a large part of the modern microbial diversity on the planet. . But oxygen is such a rich source of energy that its availability makes possible many interesting evolutionary pathways, such as the rise of complex plant and animal life. Almost all known multicellular species here on Earth breathe oxygen in some form.
The researchers found that brines from Mars could contain a large amount of oxygen, enough to support aerobic microbial life almost everywhere, if the requirements of these hypothetical insects on Mars mirrored those of Earth. And the models showed that dissolved oxygen capacity varies greatly over time and from place to place, because it depends on temperature and, to a lesser extent, pressure.
Colder temperatures promote greater oxygen input to the brines. Therefore, the researchers determined that especially cold pockets near the Martian poles could be rich enough in oxygen to support complex multicellular organisms such as sponges. Such “aerobic oases” can be common today above 67.5 degrees north latitude and below 72.5 degrees south latitude.
Defining the search
There is some observational data to support the new modeling results, according to experts. For example, the Curiosity rover has detected manganese oxides during its exploration of the 152-kilometer Gale crater on Mars. These chemical compounds can only be produced with a large amount of oxygen.
Curiosity also established the presence of brine deposits, with notable variations in the elements they contained. A high salt content allows water to remain liquid, a necessary condition for oxygen to dissolve, at much lower temperatures, making brines an ideal place for microbes.
The researchers devised a first model to describe how oxygen dissolves in salt water at subzero temperatures. And then a second model estimated climate changes on Mars over the past 20 million years and over the next 10 million years.
Taken together, the calculations showed which regions of the Red Planet are most likely to produce oxygen based on brine (around 6.5% of the entire planet can host similar amounts of oxygen to those on Earth that are sufficient to sustain the lives of some microbes and sponges), data that could help determine the location of future probes.
“Our results do not imply that there is life on Mars, but they show that Martian habitability is affected by the potential for dissolved oxygen ,” the researchers explain.
Reference: Vlada Stamenković et al. O2 solubility in Martian near-surface environments and implications for aerobic life, Nature Geoscience (2018). DOI: 10.1038 / s41561-018-0243-0
Image credit: NASA / JPL-Caltech
