On ancient Mars, sustained planetary storms may have filled lakes and rivers

New study from the University of Texas at Austin helps scientists reconstruct the ancient climate of March by revealing how much precipitation and snowmelt filled its lake beds and river valleys 3.5 billion to 4 billion years ago.

The study, published in Geology, represents the first time that researchers have quantified the precipitation that must have been present on the planet, and it comes under the name of Perseverance of Mars 2020 rover is heading towards the red planet to land in one of the lake beds crucial for this new research.

The ancient climate of Mars is an enigma for scientists. For geologists, the existence of river beds and paleolakes – secular lake basins – paints a picture of a planet with significant precipitation or snowmelt. But scientists who specialize in computer models of the planet’s climate have been unable to reproduce an ancient climate with large amounts of liquid water present long enough to account for the observed geology.

“This is extremely important because 3.5 to 4 billion years ago, Mars was covered with water. There was a lot of rain or snowmelt to fill these canals and lakes, ”said lead author Gaia Stucky de Quay, postdoctoral fellow at UT’s Jackson School of Geosciences. “Now it’s completely dry. We’re trying to figure out how much water was there and where it all went. “

Although scientists have found large amounts of frozen water on Mars, there is currently no significant amount of liquid water.

In the study, the researchers found that precipitation had to be between 4 and 159 meters (13 and 520 feet) in a single episode to fill the lakes and in some cases provide enough water to overflow and pierce the lakes. lake basins. While the range is wide, it can be used to help understand which climate models are accurate, said Stucky of Quay.

“It’s a huge cognitive dissonance,” she says. “Climate models have trouble accounting for this amount of liquid water at this time. It’s as if liquid water is not possible, but it has happened. It is the knowledge gap that our work attempts to fill. “

Scientists examined 96 open and closed basin lakes and their watersheds, all thought to have formed between 3.5 billion and 4 billion years ago. Open lakes are those that are ruptured by water overflows; those closed, on the other hand, are intact. Using satellite imagery and topography, they measured the areas of lakes and watersheds, as well as lake volumes, and took into account potential evaporation to determine the amount of water needed for fill the lakes.

By examining the ancient closed and open lakes, and the river valleys that fed them, the team was able to determine minimum and maximum precipitation. The closed lakes offer a glimpse of the maximum amount of water that could have fallen in a single event without piercing the basin side of the lake. Open lakes show the minimum amount of water needed to pass the lake basin, causing water to break to one side and precipitate.

In 13 cases, the researchers found paired basins – containing a closed basin and an open basin fed by the same river valleys – that offered key evidence of maximum and minimum precipitation in a single event.

Another big unknown is the duration of the episode of rain or snowmelt: days, years or thousands of years. This is the next step in the research, said Stucky of Quay.

As this research is published, NASA recently launched March 2020 Perseverance Rover to visit Jezero Crater, which contains one of the open lake beds used in the study. Co-author Tim Goudge, assistant professor in the Department of Geological Sciences at UT Jackson School, was the main scientific advocate for the landing site. He said the data collected by the crater could be important in determining how much water is on Mars and whether there are any signs of past life.

“Gaia’s study takes previously identified closed and open lake basins, but applies a smart new approach to limiting the amount of precipitation experienced by those lakes,” Goudge said. “Not only will these results help us refine our understanding of the ancient climate of Mars, but they will also be a great resource for bringing the results for March 2020 Perseverance Rover in a more global context. “

Reference: “Precipitation and Aridity Constraints of Paleolocons at the Beginning of March” by Gaia Stucky de Quay, Timothy A. Goudge and Caleb I. Fassett, August 13, 2020, Geology.
DOI: 10.1130 / G47886.1

This study was funded by a grant from NASA’s Mars Data Analysis Program.