Water flowing on Mars, NASA images suggest

Images taken by NASA's Mars Reconnaissance Orbiter have provided the best evidence to date that flowing, liquid water could exist on the planet.

The images, reported in Thursday's edition of the journal Science, show dark markings on the sides of Martian mountains during the warmer months of the 700-day Martian year, which appear to fade in winter and return again in the spring.

"The best explanation for these observations so far is the flow of briny water," said Alfred McEwen of the University of Arizona.

McEwen, an author of the report, added that the darkness of the markings is still a mystery.

"The flows are not dark because of being wet," he said. "They are dark for some other reason."

A possible explanation, according to researchers, is that the briny water could reorder grains of sand in a way that seems to darken their appearance, but this wouldn't explain why they brighten in lower temperatures.

NASA administrator Charles Bolden said the program, "keeps bringing us closer to determining whether the Red Planet could harbour life in some form.… and it reaffirms Mars as an important future destination for human exploration."