JPL/University of Arizona via NASA
Researchers announced this week a new development in our understanding of water on Mars. Since the Spirit and Opportunity rovers started driving around Mars, we've known that Mars had liquid water on its surface in the past—they found rocks with physical structures and chemical composition that can only be created in an underwater environment.
With the high-resolution imaging of the Mars Reconnaissance Orbiter, we've known since around 2011 that sub-surface ice can melt and create channels on the slopes of craters.
Now researchers have found that water flows on Mars today. The channels on the sides of craters show a dark coloration in the "summer" on Mars when it's just warm enough that salty sub-surface water can flow down the channels and cause the soil to look darker (think of how sand at the beach looks darker when wet).
Those dark patches fade away in Martian winters, when it's too cold for water to flow and the soil dries up. The clincher? The recently announced spectroscopic analysis of the chemistry in these regions shows they contain short-lived salts that are produced only in wet environments.
The water today on Mars is salty, and researchers are debating how conducive it is to life. It's possible that microbial life could live today on Mars in those salty regions. Whether first life could evolve on Mars is a separate question that involves a host of open scientific topics—scientists haven't yet figured out how first life on Earth developed, and are still investigating the environmental conditions at various stages of Martian history.
Water could also, of course, help support a future human mission to Mars. You can read more from NASA on their mission plans, or enjoy the speculation at the movies (the latest being The Martian with Matt Damon).
