A Brief History of Finding Water on Mars

Every once in a while, a story about water on Mars surfaces and everyone goes crazy. Usually it's because of overly sensational reportage about a newly discovered 'river on Mars'—when in fact scientists have just found weathered stones that suggest a river once flowed in a given spot on the red planet.

But this time you can believe the hype: NASA’s Curiosity rover has found water on Mars. Sort of. There aren’t any lakes or rivers, but there is water locked in the Martian soil, about two percent by volume, which translates to about two pints of water for every cubic foot of soil. And that’s significant.

We’ve known about the existence of water on Mars for a while now, in part because we’ve been looking for it for years. As it’s necessary for life as we know it, the hunt for water on Mars has gone hand in hand with the search for life on the red planet, which has been at the heart of Martian exploration since the 1960s.

The first spacecraft to successfully fly by and photograph Mars was NASA’s Mariner 9. In 1971, it returned photographs to Earth that showed that looked like eroded canyons and dry river beds scarring the landscape. When the twin Viking landers arrived five years later, their up close surface images confirmed Mariner’s findings that the Martian landscape had been shaped by water. But neither mission was able to confirm the presence of water on the surface.

The 1990s saw a renewed interest in Mars exploration. Orbiters from NASA and the European Space Agency detected the presence of minerals that suggested the presence of water near the Martian surface, the existence of subsurface water ice deposits, and superficial hot springs that create and sustain precipitation in certain areas.

But the first hard evidence of water on Mars didn’t come until 2008 with NASA’s Mars Phoenix Lander. It dug a small trench at its northern landing site and revealed bright deposits that disappeared in four days. Scientists suspected it was ice that had sublimated; Phoenix’s detection of water vapour in the atmosphere confirmed this suspicion. The twin Spirit and Opportunity rovers have both found traces of water enclosed in rock.

Now, Curiosity has added a definitive find to this history of searching for water on Mars.

The one-ton rover landed in Mars’ Gale Crater on August 5, 2012. Once it ran through its systems checks and got roving, it visited a geologically interesting site called Rocknest. The rover scooped up a small sample on Sol 71 (October 17 by Earth’s calendar) from a wind-blown ripple in the soil and transferred the soil to its onboard chemistry lab. Part of the sample ended up in SAM, the Sample Analysis on Mars instrument.

SAM heated the sample to 1,535 degrees Fahrenheit then used its gas chromatograph, mass spectrometer, and laser spectrometer to identify chemicals contained in the sample. When heated, the sample was found to contain abundance of water as well as significant quantities of carbon dioxide, oxygen, and sulfur compounds. The test also found carbonate materials in the sample—compounds that form in the presence of water.

SAM also found the sample carried oxygen- and chlorine-containing compounds—most likely chlorates or perchlorates. These are the same compounds Phoenix found in 2008 at its near-arctic landing site, suggesting chlorates and perchlorates occur globally on Mars. This might not be great news since these compounds are highly toxic to humans. But they aren’t toxic to all life forms; some microbes are known to use the oxidizing chemical for energy. So the question (or one of the many questions, rather) now is whether hypothetical microbes on Mars could metabolize perchlorates similar to their Earthly counterparts. If so, this could shift the search for life just a little, but in a good way.

Analysis of the Rocknest sample also revealed similar ratios of the gases Curiosity has sampled in the atmosphere, suggesting surface material interacts quite readily with the atmosphere.

If future Martian explorers make use of this readily available surface water, it won’t be as easy as extracting the water and pouring a glass. That the sample contains perchlorates means humans can’t drink the water without somehow filtering it to make it safe for consumption. And even then, it might taste like the dry, desolate Martian landscape. A Brita filter and some Crystal Light might be necessary to make Martian water potable for humans. In any case, this discovery of water on Mars surface, even if it’s not a flowing river, is exciting. It seems we’re inching closer to uncovering Mars’ potential living past.