Giant map reveals ancient traces of water on Mars everywhere we look

A new map, compiled for years, reveals where to find ancient traces of water on Mars.

Using data collected over the past decade by ESA’s Mars Express and NASA’s Mars Reconnaissance Orbiter, both currently orbiting the Red Planet, scientists have created the most comprehensive map to date of the specific Martian mineral deposits.

Deposits are aqueous minerals – those that have been weathered by the presence of water, such as clays.

We know there are clays on Mars; we’ve even seen some up close, or as close as we can get, via the Curiosity rover. However, a larger map of where they can be found gives us a fuller picture of Mars’ water history and will help plan future exploration of the now dry and dusty world.

And, contrary to expectations, the map shows that wherever we go on Mars, we are bound to find something interesting.

Map of traces of water detected on Mars
The new world map of aqueous minerals on Mars. (ESA/Mars Express (OMEGA) and NASA/Mars Reconnaissance Orbiter (CRISM))

Before the survey began, there were about a thousand known aqueous mineral deposits on Mars. The new work, led by planetary scientist John Carter (er, that’s scary) of the University of Paris-Saclay and the University of Aix Marseille in France, has identified many more.

The new map shows that there are at least hundreds of thousands of aqueous mineral deposits on Mars, particularly in some of the oldest parts of the planet’s surface.

“I think we’ve collectively oversimplified Mars,” Carter says.

“This work has now established that when you study ancient terrains in detail, not seeing these minerals is actually an oddity.”

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The more detailed study of these minerals can reveal the amount of water historically present on Mars.

For example, here on Earth, clays form when water and another mineral interact, resulting in a different mineral.

Vermiculites, smectites and chlorites form when water interacts with iron and/or magnesium. Al-smectites and kaolins are formed from the interactions of water with aluminum.

But the amount of water also plays a role.

The more water there is, the more the final mineral is altered. Thus, scientists can examine different mineral deposits and estimate the amount of water present when the mineral was formed.

The work of Carter and his colleagues revealed the presence of the minerals mentioned above as well as sulfate and carbonate salts through spectrometric data. It is the measurement of the light reflected by an object; the two orbiters are equipped with spectrometers whose data complement each other on the mineralogy of the Martian surface.

The resulting map suggests that there isn’t much of Mars that hasn’t been weathered by water at some point in its history. The planet may be a fairly dry place now, but evidence suggests it was never a stranger to dampness.

It also suggests that the previous reconstruction of its water history – that water formed the clays, then salts appeared as the waters dried up – might be a bit too simplistic.

Some of the salts in the new map appear to be older than some of the clays, and in some areas the two are mixed in a way that suggests they may be contemporary.

Unraveling the implications of these results will require a significant amount of analysis.

“The evolution from lots of water to no water isn’t as clear as we thought, water didn’t stop overnight. We see a great diversity of geological settings, so that no single process or timeline can explain the evolution of Mars’ mineralogy,” Carter explains.

“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.”

Another question that remains is whether the water was persistent or episodic. Was it there for a long period of time, or did it disappear and reappear periodically?

Not much can be gleaned simply from a map showing where the minerals are… but, in another article, a team led by planetary scientist Lucie Riu, then at JAXA and now at ESA , quantified the abundance of aqueous minerals as seen on the world map. .

“If we know where and in what percentage each mineral is present, it gives us a better idea of ​​how these minerals could have formed,” says Riu.

Together, the two documents constitute an important groundwork that needed to be established before answering these questions.

And, perhaps, identify the most interesting places to send future missions, crewed or uncrewed, in the quest to understand how Mars became a dry world – which, in turn, might have answers about how the Earth did not.

Both articles were published in Icarus. They can be found here and here.

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