Research on clay formation could have implications for how to search for life on Mars

December 7, 2017 by David Rothery, The Conversation
The Wdowiak Ridge on Mars as seen by NASA’s Mars Exploration Rover Opportunity. Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

Today Mars has only a thin atmosphere, and its surface is very dry with the possible exception of some localised and temporary water seeps. However, ancient eroded valley networks that were discovered by orbiting spacecraft in the early days of exploration prove that water flowed across the surface in the remote past.

The branching nature of the oldest valleys, which have many tributaries, shows that the was most likely supplied by rainfall. This means the surface was very likely habitable for life back then.

When were detected from orbit and subsequently confirmed by surface rovers, it was taken as further evidence that Mars once had a wet surface environment, hospitable to life. This is because when most rocky minerals weather away under humid conditions they rot to form various kinds of .

Clay minerals cannot form unless there is water available – it is an essential ingredient in their microscopic crystalline structure. Clays are found virtually nowhere on the red planet except in Mars's most ancient terrains, dating back to an epoch about 3.7-4.1 billion years ago, called the Noachian.

Understanding these martian clays is difficult, because they can be seen only sparsely across the surface. Some of the detected clays are in bedrock that has been exposed by erosion, others have been washed downstream from such sources by the Noachian rivers.

Branching tributaries with ancient valleys seen in a 120km wide region of Mars. GoogleEarth . Credit: ESA/DLR/FU Berlin

On Earth, clay forms by weathering of mineral grains chemically attacked by water. Most scientists believe that a similar process took place on Mars during its wet, Noachian period. However, some researchers have suggested that most of the detected clay was not formed in this way at all. They argue instead it formed prior to that, while warm water was circulating through the bedrock in response to nearby volcanic and intrusive activity.

Heat and steam from the magma ocean

Now a new study by a group from Brown University, Rhode Island, published in Nature, further challenges the idea that clay on Mars formed just like that on Earth. The team has done experiments suggesting that the origin of most of Mars's clays was even earlier. They considered the likely conditions on the hot, infant Mars, 4.5 billion years ago. At that time, the primordial that once covered the planet was still cooling, and the first crystals had floated to the surface to grow Mars's original "primary crust".

At this time, Mars very likely had a hot and steamy atmosphere, which was still degassing from inside the planet and had not yet had a chance to escape to space. Conditions would have been perfect to make clays by between the atmosphere and the minerals within the warm and porous top of the crust.

Research on clay formation could have implications for how to search for life on Mars
Artist’s impression of very early Mars, with a steamy carbon dioxide-rich atmosphere above the surface of a cooling magma ocean. Credit: David A Rothery, Author provided

The team suggests that such clay formation would have pervaded a layer up to 10km thick. This, they say, was subsequently buried by material spread across the surface by asteroid impacts and by lava from volcanic eruptions. Surface traces of clay are rare today, because they depend on the buried layer having been re-exposed by later, smaller, impacts or erosional processes that have acted locally to strip away the cover.

Not like Earth?

The evidence for flowing water in the Noachian is robust, and has not been undermined. However, if the new study is right, Mars may not have experienced a prolonged period when the conditions were right for clays to be made by weathering under humid, Earth-like, conditions.

The next Mars landers, NASA's Mars 2020 and ESA's ExoMars 2020, are both targeted at sites where clays have been detected. That's precisely because these may mark sites where Earth-like habitable formerly prevailed, and may have once hosted microbial life just like Earth.

20km wide image showing the Jezero crater, a candidate landing site for NASA’s Mars 2020 mission. Areas of clay minerals appear green. Credit: NASA/JPL-Caltech/MSSS/JHU-APL

On the balance of probabilities, these are still good places to look for traces of . The new research suggests ancient life is unlikely to be found where the clays initially formed by chemical reactions with the atmosphere – it doesn't rule out habitability at the sites where clays have been deposited. Yet, one link in the chain of logic may just have have been at least partially severed.

Explore further: Clay minerals on Mars may have formed in primordial steam bath

Related Stories

Clay Studies Alter View of Early Mars Environment

July 18, 2007

A study of the thermodynamics of clays found on Mars suggests that little carbon dioxide could have been present during their formation, which contradicts a popular theory of the early Martian atmosphere and will send researchers ...

Study finds evidence for more recent clay formation on Mars

December 14, 2015

Recent orbital and rover missions to Mars have turned up ample evidence of clays and other hydrated minerals formed when rocks are altered by the presence of water. Most of that alteration is thought to have happened during ...

Martian clay minerals might have a much hotter origin

September 12, 2012

(Phys.org)—Ancient Mars, like Earth today, was a diverse planet shaped by many different geologic processes. So when scientists, using rovers or orbiting spacecraft, detect a particular mineral there, they must often consider ...

Potential habitats for early life on Mars

May 24, 2016

Recently discovered evidence of carbonates beneath the surface of Mars points to a warmer and wetter environment in that planet's past. The presence of liquid water could have fostered the emergence of life.

Recommended for you

Major space mystery solved using data from student satellite

December 13, 2017

A 60-year-old mystery regarding the source of some energetic and potentially damaging particles in Earth's radiation belts is now solved using data from a shoebox-sized satellite built and operated by University of Colorado ...

Bright areas on Ceres suggest geologic activity

December 13, 2017

If you could fly aboard NASA's Dawn spacecraft, the surface of dwarf planet Ceres would generally look quite dark, but with notable exceptions. These exceptions are the hundreds of bright areas that stand out in images Dawn ...

Spanning disciplines in the search for life beyond Earth

December 13, 2017

The search for life beyond Earth is riding a surge of creativity and innovation. Following a gold rush of exoplanet discovery over the past two decades, it is time to tackle the next step: determining which of the known exoplanets ...

0 comments

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

Click here to reset your password.
Sign in to get notified via email when new comments are made.