New Mars water map will prove invaluable for future exploration

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A new map of Mars changes the way we think about the planet’s aquatic past and shows where we should land in the future.

The map shows mineral deposits across the planet and was painstakingly created over the past decade using data from the Mars Express Observatory for Mineralogy, Water, Ice and Activity (OMEGA) from ESA and NASA’s Mars Reconnaissance Orbiter compact reconnaissance imagery. Spectrometer instrument for Mars (CRISM).

Specifically, the map shows the locations and abundances of aqueous minerals. These come from rocks that have been chemically altered by the action of water in the past and have generally been transformed into clays and salts.

Global map of hydrated minerals on Mars

On Earth, clays form when water interacts with rocks, with different conditions giving rise to different types of clays. For example, clay minerals such as smectite and vermiculite form when relatively small amounts of water interact with rock and thus retain mostly the same chemical elements as the original volcanic rocks. In the case of smectite and vermiculite, these elements are iron and magnesium. When the amount of water is relatively high, the rocks can be further weathered. Soluble elements tend to be washed away leaving behind aluminum-rich clays like kaolin.

The big surprise is the prevalence of these minerals. Ten years ago, planetary scientists knew about 1,000 outcrops on Mars. This made them interesting as geological curiosities. However, the new map has reversed the situation, revealing hundreds of thousands of these areas in the oldest parts of the planet.

“This work has now established that when you study ancient terrains in detail, not seeing these minerals is actually an oddity,” says John Carter, Institut d’Astrophysique Spatiale (IAS) and Laboratoire d’Astrophysique de Marseille (LAM) , Paris-Saclay University and Aix Marseille University, France.

It is a paradigm shift for our understanding of the history of the red planet. From the smallest number of aqueous minerals we knew before, it was possible that water was limited in extent and duration. Now, there is no doubt that water has played a huge role in shaping geology all around the planet.

Now the big question is whether the water was persistent or confined to shorter, more intense episodes. While they don’t yet provide a definitive answer, the new results certainly give researchers a better tool to search for the answer.

“I think we’ve collectively oversimplified Mars,” says John. He explains that planetary scientists have tended to think that only a few types of clay minerals on Mars were created during its wet period, and then as water gradually dried up, salts were produced across the planet.

This new map shows that it’s more complicated than previously thought. While many Martian salts probably formed later than the clays, the map shows many exceptions where there is an intimate mixture of salts and clays, and some salts which are presumed to be older than some clays.

“The evolution from lots of water to no water isn’t as clear as we thought, the water didn’t stop overnight. We see a great diversity of geological settings, so no single process or timeline can explain the evolution of the mineralogy of Mars. This is the first result of our study. The second is that if you exclude life processes on Earth, Mars exhibits a diversity of mineralogy in geological contexts, just like Earth,” he says.

In other words, the closer we look, the more complex Mars’ past becomes.

Water-rich minerals at Jezero Crater

The OMEGA and CRISM instruments are perfectly suited to this investigation. Their datasets are highly complementary, working on the same wavelength range and sensitive to the same minerals. CRISM uniquely provides high resolution spectral surface imagery (up to 15 m/pixel) for very localized patches of Mars, and makes it best suited for mapping small regions of interest, such as the rover landing sites. For example, mapping shows that Jezero Crater, where NASA’s Perseverance 2020 rover is currently exploring, displays a rich variety of hydrated minerals.

OMEGA, on the other hand, provides global coverage of Mars at higher spectral resolution and with better signal-to-noise ratio. This makes it better suited for global and regional mapping and for distinguishing between different weathering minerals.

The results are presented in a pair of articles, written by John, Lucie Riu and their colleagues. Lucie was at the Institute of Space and Astronautical Science (ISAS), Japanese Aerospace eXploration Agency (JAXA), Sagamihara, Japan, when some of the work was done, but is now an ESA researcher at the European Center for Space Astronomy (ESAC) of ESA in Madrid.

With the basic detections in hand, Lucie decided to take the next step and quantify the quantities of minerals present. “If we know where and in what percentage each mineral is present, it gives us a better idea of ​​how those minerals could have formed,” she says.

This work also gives mission planners excellent candidates for future landing sites – for two reasons. First, aqueous minerals still contain water molecules. Together with the known locations of buried water ice, this provides possible locations to extract water for in situ resource use, key to establishing human bases on Mars. Clays and salts are also common building materials on Earth.

Water-rich minerals in Oxia Planum

Second, even before humans got to Mars, aqueous minerals provide fantastic places to do science. As part of this mineral mapping campaign, the clay-rich site of Oxia Planum was discovered. These ancient clays include the iron- and magnesium-rich minerals of smectite and vermiculite. Not only can they help unlock the planet’s past climate, but they’re perfect sites for determining whether life began on Mars. As such, Oxia Planum was proposed and ultimately selected as the landing site for ESA’s Rosalind Franklin rover.

“That’s what interests me, and I think this kind of mapping work will help open up these studies in the future,” says Lucie.

As always when it comes to Mars, the more we learn about the planet, the more fascinating it becomes.

Notes for Editors

A Mars orbital catalog of aqueous weathering signatures (MOCAAS) by J. Carter et al is in press in Icarus.

The M3 project: 3 – Global distribution of the abundance of hydrated silicates on Mars by L. Riu et al is published in IcarusVolume 374, 2022.

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