Evidence grows for liquid water on Mars

Example of recurring slope lineae (RSL) in Horowitz crater on Mars. Credit: NASA/JPL/University of Arizona

Is there still liquid water on Mars? That has been one of the longest-running and most debated questions about the Red Planet. Mars has tons of water, but it is frozen in the polar ice caps and in extensive regions of permafrost underground around the planet. The thin atmosphere does contain water vapour – enough for clouds, fog, frost and snow, but it is too thin and cold for liquid water to exist on the surface.

There might be one exception however. It’s been postulated that small amounts of salty liquid water brines could persist on the surface for short periods of time. The salts allow the water to remain liquid despite the thin atmosphere (and less atmospheric pressure) and cold temperatures. Experiments on Earth have supported this idea.

They may have even been observed directly by the Phoenix lander which landed in the Martian arctic near the north pole – small droplets were seen forming on one of the lander’s legs after landing which had the appearance of water droplets. They grew, merged and slowly moved down the leg before sublimating. Phoenix wasn’t able to analyze them directly, but they looked and behaved like briny water droplets, and the soil, like in other places on Mars, was found to contain both water ice and salts. The theory is that heat from the spacecraft caused the droplets to form, possibly from the exhaust during the landing itself.

Last year, other possible evidence for such brines was found in photographs taken from orbit by the Mars Reconnaissance Orbiter spacecraft. Dark linear markings on slopes which looked a lot like liquid flowing downhill. Unlike some other streaks which might be explained by dry processes such as landslides, these ones appear during warmer months on slopes which face the equator and recur seasonally. They move downhill as dark streaks before eventually fading, as water would be expected to do.

Last week, scientists provided an update on these tantalizing features at the Lunar and Planetary Science Conference in Texas; they have not been able to come up with an explanation that doesn’t involve briny water. The number of known locations of these “recurring slope lineae” (RSL) has more than doubled, up to 15 from the previous seven. There are also currently 23 other candidates, although they haven’t yet been shown to recur; that will require further observations.

On Earth, there are similar features in Antarctica, where salty groundwater seeps downhill through the soil. According to Joe Levy of Oregon State University, “The RSL and the [Antarctic] water tracks are both flowing like water through sediment. If it moves like water, it may very well be water.”

The evidence suggests that water may indeed still flow on Mars, albeit in small amounts. If true, it adds to our understanding of how Mars is similar to Earth in some ways (and, based on other evidence, used to be much more so in the past).

This article was first published on Examiner.com.