Thick salt deposits have long been associated with evidence of ancient oceans on Earth. So when astronomers spotted quantities of salt on Mars, it caused them to question whether they meant Mars also once boasted oceans of its own. However, what these salt deposits really mean about the Martian climate has continued to elude scientists – until now.
Researchers have now offered a new method for testing what Mars’ water would have looked like.
Curiosity has an excellent instrument package, so it's possible we could get some very interesting data
Dr Mohit Melwani Daswani
Professor Edwin Kite, of the University of Chicago, the study’s author, 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.”
The salt in Martian deposits is different from the salt found in Earth’s oceans.
The Martian version actually resembles to Epsom salts, made from two ingredients: magnesium and sulphuric acid.
Life on Mars: NASA's Mars Curiosity rover will reach the salt deposits in 2020 (Image: NASA)
Understanding how those two chemicals combined tells scientist about the nature of early Mars’ climate.
One theory is Mars once had water that circulated deep underground, ferrying magnesium to the surface where it reacted with sulphuric acid.
This would have meant Mars would have once been warm enough to allow groundwater to flow freely.
Another theory posits the magnesium simply blew in as dirt, meaning the climate could have been as cold as the Antarctic.
The scientific analysis focussed on the fact there is too much Martian salt to have been deposited as a one-time dry-out.
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The water would have had to continually collect salts, evaporate and transition into liquid water.
Each time this cycle repeated, as the water drained into the ground, it would have carried particles of carbon dioxide from the atmosphere with it.
Curiously, while too much carbon dioxide in the atmosphere can warm a world, too little will freeze it.
If too much carbon was locked into the Martian 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.
Although this dents the groundwater theory, it does not disprove it, Professor Kite claims.
He added: ”Most of our model runs disfavoured 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 Mars Curiosity rover can test this theory when it arrives at a salt deposit next year.
“Curiosity has an excellent instrument package, so it’s possible we could get some very interesting data,” said study co-author Mohit Melwani Daswani, of the NASA Jet Propulsion Laboratory.