NASA's New Evidence of Water on Mars Suggests It's Hiding Underground

When it comes to planetary exploration, NASA’s mantra has always been “follow the water.” Water is essential for life on Earth, so water or traces of it on other planets is the best bet to find extraterrestrial life, past or present. Nowhere have we been on a water hunt like we have been on Mars.

There are currently two rovers and three orbiters studying the planet, and last week one returned something really exciting–and possibly soggy. New pictures from NASA’s Mars Reconnaissance Orbiter suggest there’s currently water lurking in underground crevices inside the McLaughlin Crater.

Launched in 2005, MRO and its suite of six onboard instruments have provided more high-resolution data about the Red Planet than all other Mars orbiters combined. One instrument, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is designed to read the chemical signatures of minerals like carbonates that are best preserved under non-acidic conditions.

The McLaughlin Crater is massive, measuring 57 miles across and 1.4 miles deep. That’s deep enough that underground water, water that may remain hidden, could have flowed into the crater. And McLaughlin is in the right geographical location for underground water to pool. The crater sits at the low end of a regional slope several hundreds of miles long on the western side of the Arabia Terra region, it lacks large inflow channels, and is marked by small channels in the crater wall that could be the border of a lake.

But it’s what’s inside the crater that counts. Using CRISM data, scientists have found spectroscopic evidence that the layered rocks at the bottom of the crater contain traces of carbonates and clay minerals. These are things that need water to form on Earth, meaning its likely liquid water filled McLaughlin at some point in Mars’ ancient past. And adding to the interest, there’s more evidence suggesting the carbonates formed inside an ancient lake than suggests they were washed in from some outside source.

This discovery supports the theory that simple life forms once thrived in hidden underground Martian waters. And like all things life-related, it’s the comparison with Earth that makes the case so strong.

On Earth, microbes living up to three miles underground account for a significant percentage of the entire planet's living matter. These underground life forms are largely primitive microbes, but life is life. And it’s likely that microbes this far beneath the surface could have survived the Late Heavy Bombardment period, a series of cosmic impacts the inner planets endured between 4.1 billion to 3.8 billion years ago.

So say the same thing happened on Mars around the same time – primitive microbes sprung up in underground lakes and survived the Late Heavy Bombardment. What happened? Well, Mars’ gravity is a little more than a third of what we feel on Earth and its crust is a little less dense. This means that while the planet is dry now, more water could have leaked underground in the past. And if it didn’t all evaporate, it could be that energy sources and chemical reactions similar to those that support deep-dwelling organisms on Earth – like every astrobiologist’s favourite, the deep sea hydrothermal vents –  could have done the same thing on Mars. Or might be doing the same thing on Mars right now.

For the time being there aren’t any missions planned to go digging into Mars‘ deep underground for find subsurface water. But there are other ways scientists can figure out what happened, or is happening, inside the red plant. Deep rocks exhumed by erosion or meteorite impacts, for example, can reveal the planet’s inner makeup. Likewise, evidence of materials produced in a wet environment could be just as scientifically beneficial. NASA’s InSight mission, set to launch in 2016, will drill into the surface. It won’t go too far down, but it will help scientists understand what’s going on inside the planet, and that might shed more light on the subsurface lake theory.