Caitlin: People have been talking about Mars a lot lately, and for good reason. Water on Mars is super exciting, but Mars used to have way more water in the form of huge lakes and rushing rivers, and two recent discoveries are teaching us more about what that world would have looked like.

The Curiosity rover has been roaming around Mars's Gale Crater since 2012 collecting data on what the rocks in the crater are made of. When mission scientists analyzed the data in 2013, they found that the rocks contain minerals that could only have come from ancient freshwater lakes, which probably existed more than 3 billion years ago.

Now, in a new study published last week in the journal Science, scientists looked at the layers of rock making up the base of Mount Sharp, a mountain smack in the middle of the crater. And based on how the layers of rocks were arranged, they found that the ancient lakes in Gale Crater were probably a few meters deep. That's definitely deep enough for Mark Watney to snorkel in.

The group also used the data to estimate the lake would've stuck around for 100 to 10,000 years at a time, freezing and melting over the course of 10,000 to ten million years as the martian climate changed. The researchers pointed out that even though the above ground lakes disappeared every so often, the groundwater table below the surface was probably there the whole time, rising and falling depending on the conditions.

So why is this so exciting? The longer the water was around, the more likely it is that some type of life had time to evolve. Now on another paper published this week in the journal Nature, a group of American and Hungarian scientists also looked at some of Curiosity's data on the sediment in Gale crater, but this time they were trying to figure out what ancient Martian rivers looked like.

Part of what makes Gale Crater so fascinating is that it has an Alluvial fan, a pattern of sediment that develops as streams and rivers deposit layers of rock in the shape of a cone, and some of those rocks are round pebbles which got smoothed out as they were carried along the riverbed by the rushing Martian water.

When the scientists first compared the rocks Curiosity found with similar-looking round rocks here on Earth, they originally thought it probably took at least a few kilometers of river to smooth them out. But the group behind the new study wanted a more specific estimate, to get a better sense of how a big a river could have made such smooth river rocks. 

So they stuck eighty rocks in a rotating drum, stirred them with a paddle and measured how much they changed over time. They then ran the numbers that came out of that experiment on the Martian pebbles and it turns out Mars's rivers might have been much longer than we thought.

The pebbles probably came from north of Gale crater, just like earlier studies suggested, but the river probably moved the rocks about fifty kilometers, opposed to previous estimates of around twenty. The team points out that beyond just showing us what ancient Martian rivers might have looked like, this model could be used to learn about rocks in other places, like on Saturn's moon Titan or even on asteroids.

So no potato plants on Mars to report but at one point, there definitely would have been enough water on Mars to support them.

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