Mars gullies likely contain 'no water', study says

This NASA/JPL/University of Arizona image obtained June 7, 2015 shows a close-up of a "fresh" impact crater in the Sir
This NASA/JPL/University of Arizona image obtained June 7, 2015 shows a close-up of a "fresh" impact crater in the Sirenum Fossae region of Mars captured by the High Resolution Imaging Science Experiment camera on March 30, 2015

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

Rather than water flows like those on Earth, these Martian gullies were likely created by defrosting, a duo of French scientists wrote in the journal Nature Geoscience.

"The role of in gully formation should... be reconsidered, raising the question of the importance of its occurrence in Mars' recent past," wrote Francois Forget and Cedric Pilorget of the French national research institute CNRS.

They said their findings held no implications for the headline-making announcement in September that dark lines running down slopes in the tropics of Mars in summer, may be streaks of super-salty brine—hinting at the presence of life-sustaining water.

Monday's paper dealt with 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, said the French team.

They had set out to 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.

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

Image captured by NASA's Hubble Space Telescope shows a close-up of the Red Planet Mars when it was just 34,648,840 miles away
Image captured by NASA's Hubble Space Telescope shows a close-up of the Red Planet Mars when it was just 34,648,840 miles away

Pilorget and Forget looked for answers in a thin layer of frozen carbon dioxide (CO2) observed to be present in periods that gullies were being formed.

They used computer simulations to show that thawed and trapped CO2 gas building up beneath the surface ice layer would eventually break through the soil and trigger flows of gas and debris.

No similar processes are known to occur 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."

Nothing could be excluded, though, and "other complimentary processes may be at work," he said.

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

This NASA image obtained October 9, 2015 shows a view from the "Kimberley" formation on Mars taken by NASA's Curiosity
This NASA image obtained October 9, 2015 shows a view from the "Kimberley" formation on Mars taken by NASA's Curiosity rover

In September, scientists said seasonal streaks on Mars dubbed "recurring slope linaea" may be briny flows.

They found evidence of hydrated salt minerals in the lines, which they said implied liquid water was present, even as others cautioned against reading too much into the results.

"Our study has no link to the announcements made in September," said Forget, a planetologist.

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

It is widely accepted that the Red Planet once had plentiful water in liquid form, and still has some today—albeit frozen in ice underground.

Earlier this year, NASA said almost half of Mars' northern hemisphere had once been an ocean, reaching depths greater than 1.6 kilometres (one mile).


Explore further

What have we learned from the discovery of liquid water on Mars?

More information: Nature Geoscience, DOI: 10.1038/ngeo2619
Journal information: Nature Geoscience

© 2015 AFP

Citation: Mars gullies likely contain 'no water', study says (2015, December 21) retrieved 17 July 2019 from https://phys.org/news/2015-12-mars-gullies.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
1089 shares

Feedback to editors

User comments

Dec 21, 2015
Next in the series of papers; How to tax the gullies for their reckless use of CO2.

Dec 21, 2015
Oh look, the remnants of a ROMAN road on Mars!!!! ;-)

Dec 21, 2015
How many more ideas do they have to discard before they will possibly, maybe, begrudgingly, consider electrical/plasma processes?


Dec 22, 2015
How many more ideas do they have to discard before they will possibly, maybe, begrudgingly, consider electrical/plasma processes?


Loads, including the possibility that they are unicorn tracks. It has just as much evidence in favour of it.

Dec 22, 2015
While Pilorget and Forget may have done a good job simulating the conditions on Mars, it does not appear that explains the visual features of the recurring slope linea (RSL). The clearly defined edges of RSL imply a substance with significant cohesiveness and inertia, i.e., a liquid flowing downhill. Unlike liquid water with dissolved solutes, liquid carbon dioxide vaporizes immediately on Mars (and Earth) because it requires at least 5.1 atmospheres of pressure. Vaporizing carbon dioxide would probably produce a more generalized pattern of leaking gas and liquid carbon dioxide can't exist anywhere near the surface of Mars in any routine way. If one takes into account that the average relative humidity on Mars is nearly 100% (near the triple point), it is less surprising that occasionally conditions allow for liquid water to flow on Mars. Looking at the article, NASA already concluded that liquid water is key.

Dec 22, 2015
How many more ideas do they have to discard before they will possibly, maybe, begrudgingly, consider electrical/plasma processes?


Loads, including the possibility that they are unicorn tracks. It has just as much evidence in favour of it.

This comment coming from a rube who is not aware of electrochemistry in plasmas. This is the type of guy who continued to believe " heavier than air flight" was impossible years after it was accomplished. Needless to say, commentary from a pulpit of ignorance is less than worthless, same as jd himself.

Dec 25, 2015
D'uh, 'complimentary' is a freebie. 'Complementary', they meant...

Still, despite their spiel-chequer's gaffe, it is nice work.

Dec 25, 2015
Looks like the propagandists for NOT exploring Mars have been hard at work again in this 'dis-information' article. Question is just what hostile state or salafist actor hired this chap.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more