The National Aeronautics and Space Administration (Nasa), the US space agency, announced last week that flowing water almost certainly exists on Mars today. From high-resolution images, scientists have discovered evidence of hydrated salts that are produced by salt, or briny, water. The images were gathered by the Compact Reconnaissance Imaging Spectrometer for Mars (Crism) onboard the Mars Reconnaissance Orbiter (MRO) spacecraft. Images were taken of four separate locations.

The phenomena that were targeted were dark streaks, known as slope lineae. These are narrow streaks, which are less reflective of light than the surrounding terrain, which occur on Martian slopes during warmer months. They appear and grow slowly, down the slope, in these periods.

In the abstract of their paper published in the journal Nature Geoscience, the research team (led by Lujendra Ojha of the Georgia Institute of Technology), who made the discovery, stated that they found “evidence of hydrated salts in all four locations in the seasons when recurring slope lineae are most extensive, which suggests that the source of hydration is recurring slope lineae activity”. The salts detected are magnesium perchlorate, magnesium chlorate and sodium perchlorate. “Our findings strongly support the hypothesis that recurring slope lineae form as a result of contemporary water activity on Mars,” concluded the abstract. However, the source of the briny water is not yet known.

At the Nasa press conference announcing the discovery, the agency’s director of planetary science, Jim Green, observed that “Mars is not the dry, arid, planet we thought of in the past.” Nasa Mars Exploration Programme lead scientist Michael Meyer pointed out that “[i]t took multiple spacecraft over several years to solve this mystery, and now we know there is liquid water in the surface of this cold, desert planet. It seems that the more we study Mars, the more we learn how life could be supported and where there are resources to support life in the future.

“These observations are giving us a much better view that Mars has resources that are useful to future travellers . . . ,” said Nasa associate administrator (and former astronaut) John Grunsfeld. “I think we will send humans in the near future to Mars . . . to be able to live on the surface, the resources are there.” In the Nasa press release that followed the briefing, he noted that “[o]ur quest on Mars has been to ‘follow the water’, in our search for life in the universe and now we have convincing science that validates what we’ve long suspected. This is a significant development, as it appears to confirm that water – albeit briny – is flowing today on the surface of Mars.”

Ojha originally observed the slope lineae in 2010 when he was an undergraduate student at the University of Arizona. He was studying images from the High Resolution Imaging Science Experiment (Hirise) carried by the MRO. Hirise has since detected slope lineae at many places on Mars. What Ojha’s team of eight researchers did was to combine Hirise images with mineral mapping images from Crism.

Perchlorates can prevent water from freezing in temperatures as low as –70° C. They had already been identified in Martian soil by two other Nasa probes, the Phoenix lander and the Curiosity rover. However, this latest study is the first in which they have been identified in their hydrated form and the first time they have been detected from orbit.

The MRO was launched in August 2005 and has been orbiting and observing the Red Planet since March 2006. It has already exceeded its original intended life span and, even including major manoeuvres executed in July and planned for September 2016, October 2016 and April 2017, is expected to have enough fuel to operate until 2036. It is equipped with six instruments, with which it studies the Martian atmosphere, surface and subsurface.