Wednesday, October 27, 2021

Astronomers Finally Know What Force Shaped Ancient River Valleys on Mars

It may be as dry as desert bones these days, but Mars was once so wet that entire landscapes were shaped by running water.

Wild floods caused thunderstorms in the Red Plains dug trenches in the Martian surface and dumped massive amounts of sediment that changed the shape of the landscape. And, unlike such landscape-changing water movement on Earth, they happened quickly, over a time span of just a few weeks.

According to a newly published study, these floods were caused by lakes filling craters on the surface of Mars, and were more common than we thought.

“If we think about how sediment was being transported across the landscape on ancient Mars, the lake break-up flood was a really important process globally,” says geoscientist Tim Gouz of the University of Texas at Austin.

“And this is a slightly surprising result because they have been treated as one-sided anomalies for so long.”

Compared to Earth, Mars is full of craters. This is because processes such as erosion and tectonic activity have eroded much of the impact crater from Earth’s surface; As a result, the surface profiles of the two planets are very different. On Mars, the abundance of ancient craters meant that, billions of years ago, when the Red Planet was still wet, crater lakes were very common.

We know that when these lakes fill up too much, they break down the walls of the craters and cause catastrophic flooding in the surrounding landscape. Previous research studying satellite imagery has revealed some of these ruptured craters, and their flooding in deep canyons, carved into the nearby landscape.

This time, Gauge and his team took a different approach. Instead of examining individual craters and their surroundings, their study includes 262 broken crater lakes, and how they globally shaped the surface of Mars.

Thanks to years of satellites orbiting the Red Planet, we have a lot of detailed imagery covering the surface of Mars. From this, we have existing maps of river basins around the world. The researchers took these maps and placed the river basins into two categories: those that were physically connected by a crater breach, and those that formed away from the crater, suggesting a more gradual formation process.

In addition, he calculated the volume of eroded valleys based on depth and width measurements obtained by satellite measurements – and made a surprising discovery.

The canyon system surrounded by crater breach floods only accounts for 3 percent of the length of the basins eroded by water on the Martian surface. But this 3 percent was much deeper than other river basins – the crater flood basins had an average depth of 170.5 m (559 ft), compared to the 77.5 m (254 ft) average depth of successive basins.

With all the data added up, crater flood basins account for at least 24 percent of the volume of river basins on Mars.

Because the impact was so rapid, the team found that it could have had a lasting effect on the surrounding landscape and river systems, despite the brief duration of the flood. The deep valleys carved by the flood would have dropped the local base level, setting new low levels for water flow. This will have a significant impact on the already existing river systems.

All of this could explain some features of Mars’ topography that are usually attributed to climate, such as convex river valleys, the researchers said. Instead this topography may be a response to disruption at the base level due to crater breach flooding.

It also highlights how important it is to assume that processes here on Earth will occur in the same way on other planets. Although the rocky worlds of the Solar System have many similarities, their differences can be enormous.

“When you fill [the craters] With water, that’s a lot of stored energy that has to be released,” Gauge said. “It makes sense that Mars could, in this case, point toward being shaped more catastrophically than Earth.”

research has been published in Nature.


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