Salt deposits on Mars hold clues to sources of ancient water

The study offers a way to test whether water flowed deep underground on Red Planet.


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For decades, Mars has been tested with whispers of water’s presence. Scientists recently saw huge deposits of salt on Mars and wondered, regardless of whether it implied Mars, too, once had giant seas. However, it’s remained unclear what those deposits implied about the Red Planet’s climate.

In a new study, scientists at the University of Chicago shake up the image of Martian salt—and offer better approaches to test what Mars’ water would have resembled.

Study author Edwin Kite, assistant professor of geophysical sciences at the University of Chicago and an expert in both the history of Mars and climates of other worlds, said, “They’re not in the right places to mark the deaths of oceans, but they date from when Mars’ climate transitioned from the early era of rivers and overspilling lakes to the cold, desert planet we see today. So these salt deposits might tell us something about how and why Mars dried out.”

Scientists observed that the salt on Mars is not the same as the Earth’s oceans, instead, it is much more similar to Epsom salts, made out of two ingredients: magnesium and sulfuric acid.

Scientists noted, “Figuring out how those two chemicals combined can give us information about what Mars’ climate used to look like.”

One probability is that Mars had water that circulated deep underground, conveying magnesium to the surface, where it reacted with sulfuric acid. That implies the planet would have been warm enough to permit groundwater to flow. Another possibility is that the magnesium was blown in as dirt. In this case, the climate could be as cold as the coast of Antarctica.

To study the groundwater scenario, scientists built models to see whether their assumptions would be realistic. But, the analysis zeroed the fact that there’s so much Martian salt that it couldn’t be deposited as a one-time dry-out—the water would need to repeatedly get salts, evaporate, transform once more into liquid water, and repeat the cycle.

Each time this occurred, as the water depleted into the ground, it would have carried out a little bit of carbon dioxide from the atmosphere with it.

Professor Kite explained, “The problem is, while too much carbon dioxide in the atmosphere warms the planet—as we’re finding out on Earth—too little will freeze it. If too much carbon was locked into the ground and the resulting atmosphere was too thin to keep Mars warm, the groundwater movement would halt as the planet froze. And the analysis found the cycle would lock up a lot of carbon.”

“This doesn’t sound promising for the groundwater scenario, but it doesn’t disprove it. Most of our model runs disfavored groundwater, but we also found a few ‘loopholes’ that could allow Mars to keep enough carbon in the atmosphere.”

“Fortunately, there would be signals that NASA’s Curiosity rover (currently on Mars) could test when it arrives at a salt deposit—hopefully in 2020.”