Mars may have once had a dense atmosphere with plenty of water and oceans that could have covered as much as two-thirds of its northern hemisphere. For reasons unknown, however, that is no longer the case.
NASA's discovery of water on Mars by the Mars Reconnaissance Orbiter suggests that it's not as dry as previously believed — and that it might not be such a dead planet after all.
The new discovery follows another in 2010 by University of Arizona undergrad student Lujendra Ojha, who found that transitory streaks along the sides of hills and cliffs on Mars looked very much like running water. The streams appear in the spring and summer seasons on Mars – which is when liquid water would be most likely to exist on the planet – with those streaks disappearing in winter and fall.
What was missing, however, was chemical evidence of water — which is what was just published in Nature Geoscience. The paper details the presence of perchlorates – which are essentially hydrated salts – wherever the streams, called "recurring slope lineae," are found.
So what does this all mean? Well, running water suggests that there is a much higher chance of life on Mars.
So far, Earth is the only planet that we know has life, occupying a zone around the sun called the "habitable zone" — which is the distance from the sun that allows for liquid water. But does this hold up for Mars?
While we already know that water exists on Mars, it is largely either frozen, gaseous or trapped underground. If organisms were to exist on Mars, they would be most likely be found in the stable underground reservoirs of water rather than the transient-state water at the surface. Of course, it's too early to conclude that life exists – or existed – on Mars at all.
While it's still unknown whether or not there could be life on Mars, the discovery will support NASA in getting ready to send astronauts to Mars.