Water - or Not? New Study Suggests Mars Gullies Are Dry

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Mars Gullies Contian ' No Water' According to New Study

Months after scientists announced "the strongest evidence yet" of liquid water on Mars, a study released Monday said there was none at least in the valleys carved into numerous Red Planet slopes.

Mars gullies, for the most part, are dry.​

A pair of French scientists, Francois Forget and Cedric Pilorget, of the French national research institute CNRS, believe these flows were likely created by the defrosting of dry ice.

As they wrote in the journal Nature Geoscience, which was released this last Monday:

The role of liquid water in gully formation should... be reconsidered, raising the question of the importance of its occurrence in Mars' recent past.

Their findings, they clarified, have no impact on the announcement in September that dark lines running down slopes in the tropics of Mars in summer, may be streaks of super-salty brine.

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The reason --  their study focused on completely unrelated geological features in a different part of the planet, mainly in the mid-latitude range between 30 and 60 degrees, on pole-facing cold slopes.

Mars gullies are dry

The intent had been to study and explain the origins of small channels carved into crater walls, hills and other martian protrusions. When first discovered, these gullies were interpreted as runoff from melting water ice or groundwater leaks that occurred hundreds of thousands of years ago.

In recent years, however, it was discovered that gully formation was ongoing, in spite of Mars being too cold for liquid water to exist.

The French team, Pilorget and Forget,  looked for answers in a thin layer of frozen carbon dioxide (CO2) that was observed when the gullies were formed -- the dry ice, in other words.

Through computer simulations, the team showed that the CO2 gas trapped beneath the surface ice layer would thaw during warm periods and build up enough pressure to break through the soil and trigger flows of gas and debris.

There's nothing like it on Earth.

Pilorget, an astrophysicist, said dry ice melt may not be responsible for all gully formation on Mars, but in cold areas with very young gullies, the gassy theory "must be favoured."

Other, complimentary, processes may also be at work, he added, so nothing should be excluded. As Pilorget explained:

For example, gullies have been detected in regions closer to the equator which are probably created by different mechanisms.

But what about those "briny flows" announced last September -- those "recurring slope linaea"?

In those announcements, NASA scientists announced they had found evidence of hydrated salt minerals, which they said implied liquid water was present, even as others cautioned against reading too much into the results.

But, again, Forget, a planetologist, said their study did not contradict those findings.

Our findings show that at least some gullies, maybe all, do not have liquid water and that the areas where they are found are not conducive to hosting liquid water, or life.

So, while it is widely accepted that the Red Planet once had plentiful water in liquid form, and still has some today, the results of this study on these Mars gullies prove one thing ...

... Mars has a lot to teach us.​

What do you think of this new study? Leave your comments below.​

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