Evidence of ancient water on Mars is a big deal, as it bolsters the theory that, at one point in the Red Planet’s past, it was capable of supporting life. This naturally prompted further investigation, so Curiosity targeted Gale Crater, which showed signs of having been a lake on Mars billions of years ago.

Now, a new theory suggests that acid rain and erosion may be responsible for much of Gale’s geological makeup, which raises an interesting question: Water we going to do about it?

Water, Water … Somewhere?

There’s no doubt that Mars once had water. What’s less certain is exactly how much water it had and how it got there. Finding these answers will be tricky since we’re looking at the end result and trying to interpret what led up to the current conditions. Sure, it was wet, but when and how did Mars dry up?

Unsurprisingly, there’s no clear consensus here. For example, the Mars Ocean Hypothesis suggests that four billion years ago the planet had enough water to create a massive ocean 100 to 1,500 meters deep. Low Martian gravity made it possible for much of this water to escape into space, and the planet eventually dried out as a result. But another theory suggests that off-planet evaporation wasn’t enough to account for all of Mars’ water, and some of it — between 30% and 99% — remains trapped in the crust.

As NPR notes, a new study from Washington University in St. Louis suggests that the Red Planet’s size and mass (one-half and one-tenth of Earth’s, respectively) made it impossible for oceans to form. Instead, the escape of elements into space happened rapidly enough that oceans were out of the question. If this is true, it challenges the notion that primordial conditions for life on Earth may have once been mirrored on Mars.

Martian lakes, however, seemed relatively safe from this scientific back-and-forth — until now.

Don’t Rain on My Parade

Existing interpretations of data suggest that Gale Crater once held massive amounts of water, possibly as one giant lake on Mars or as a series of smaller lakes and rivers. It’s part of why Curiosity went exploring Gale Crater. Given its position straddling the “hot” and “cold” sides of Mars, the crater could have been a primordial cauldron of life.

According to a new study from the University of Hong Kong, however, the amount of water present may have been much smaller than originally thought. Instead of deep lakes and rivers, the study’s authors suggest that wind, acid rain and erosion are responsible for currently observed conditions.

While there’s no disputing the presence of mineral-rich sediment, the Hong Kong study challenges the notion that the hardened sediment that now makes up Mount Sharp in the middle of Gale Crater is the result of slowly evaporating lakes. Instead, it suggests that the metrics used to study sediment deposits on Earth don’t account for Martian conditions.

As a result, the Hong Kong team says it’s more likely that minerals were carried by Martian winds to the site and then weathered over time by acid rain. They don’t deny the existence of water in Gale Crater but, rather, point to a landscape dotted with small ponds instead of one covered by deep, dark lakes.

Curiosity, Perseverance and the Future of the Mystery

While the new theory offers a new interpretation of existing data, it’s by no means a sure thing. Professor Paul Byrne, associate professor of planetary science at North Carolina State University, notes that, “There seems to be a great amount of evidence for water having been ponded in Gale Crater for substantially long time scales.” If so, a complete accounting of the minerologies and morphologies of existing sediments would be required to offer more substantial support.

Curiosity led the way with its collection of Gale Crater data. Now, Perseverance is headed for Jezero Crater — which is similar to Gale in many respects — on a hunt for more data about the interaction of rivers, lakes and rain on Mars.

NASA’s newest rover may offer a way to solve one of the biggest challenges in off-planet science: data at distance. Without samples in hand, researchers can only interpret information rather than directly confirm observations. Perseverance, however, will not only analyze Martian sediment but also collect samples that will eventually be brought back to Earth, enabling researchers to finally get their hands on a piece of the Red Planet.

Although it’s unlikely that a small amount of dirt and rocks will crack open the water mystery of Mars immediately, they could offer the opportunity for more in-depth analysis and hopefully help settle the question of whether massive lakes on Mars were the historical norm, or whether acid and erosion reigned supreme.

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