How Much Water Should we Bring to Mars?

Researchers suggest that part of the water on Mars may have been sucked up by the planet’s volcanic, sponge-like rocks.

As neighbors in the Solar System, Mars and Earth are subject to pretty much the same conditions, but they’re two strikingly-different rocky planets.

While liquid water has always been present on Earth, giving it its lively blue color, Mars, if it ever had any, has lost most its surface water and become dry, red, and apparently lifeless.

Now, scientists from Oxford University provide new clues about the fate of the red planet’s water.

Where has all the Martian Water Gone?

In a very distant past, billions of years ago, the atmosphere of Mars was probably similar to that of Earth and allowed the existence of liquid water on its surface.

Probes sent to Mars gathered data that point to traces of ancient rivers, lakes, and perhaps even an ocean.

Unfortunately, Mars couldn’t hold its surface liquid water for long because of a very low atmospheric pressure and temperature.

In 2015, NASA announced, with fanfare, the indirect discovery of recurring seasonal flows of briny water on Martian slopes (Recurring Slope Lineae, RSL), thanks to data gathered by the Mars Reconnaissance Orbiter.

However, this information is now being challenged by a new study that dashed rising hopes of finding liquid water on Mars.

Researchers from the U.S. Geological Survey, the Planetary Science Institute, the University of Arizona, and Durham University in England reviewed the same data and concluded that the recurring streaks, RSL, visible on Mars, are more likely to be avalanches of sand and dust, not water.

According to previous scientific positing, after the planet lost its magnetic field, Martian water either evaporated into solar winds or remained in the form of sub-surface ice.

While the role of the planet’s magnetic field in the disappearance of water from its surface has been supported, this alone can’t explain where all of the Martian water went.

A team of scientists at Oxford set out to assess how Mars’ mineralogy could have affected the planet’s surface, and thereby the water on it.

Martian Rocks Hold a Part of the Answer

Researchers at Oxford’s Department of Earth Sciences employed the same computer models used to study the composition of rocks on Earth to find out how mineral rocks on Mars contributed to the loss of the surface water.

Indeed, the team found that Martian basaltic rocks retain about 25% more water, compared to their counterparts on Earth, and suck it into the subsurface.

On rocky planets, like Earth and Mars, erosion and hydrothermal reactions modify the rocks on the surface. But rocks on Mars seem more prone to such reactions because of their mineral composition, and the tectonic plates (or lack thereof) play a role in that.

Oxford’s Jon Wade, lead author of the study, explains:

“The Earth’s current system of plate tectonics prevents drastic changes in surface water levels, with wet rocks efficiently dehydrating before they enter the Earth’s relatively dry mantle. But neither early Earth nor Mars had this system of recycling water. On Mars, (water reacting with the freshly erupted lavas’ that form its basaltic crust, resulted in a sponge-like effect. The planet’s water then reacted with the rocks to form a variety of water bearing minerals. This water-rock reaction changed the rock mineralogy and caused the planetary surface to dry and become inhospitable to life.”

Follow the Water

According to researchers, besides the differences in the mineral (iron) content of the Martian rocks that leads to water being drawn into the mantle, the planet’s small size also comes into play as a contributing factor.

While Wade and his team agree about the role of solar winds in the disappearance of some of Mars surface water, they think that larger quantities than previously thought could be locked up inside the mantle.

This could come in very handy for future Mars colonizers, who will have to rely on ISRU (in-situ-resource utilization) practices. Maybe they’ll find a way to extract water from Martian rocks.

The researchers say they will use the same method to find whether water could have been sucked up by rocks on other rocky planets.