Rivers on Early Mars

Planetary researchers from the University of Texas at Austin and NASA’s Marshall Space Flight Center have used dry paleolakes and riverbeds to determine how much precipitation was present on Mars 3.5-4 billion years ago.

Open and closed lakes on early Mars. Image credit: University of Texas at Austin.

Open and closed lakes on early Mars. Image credit: University of Texas at Austin.

The climate of the ancient Mars is something of an enigma to scientists. To geologists, the existence of riverbeds and paleolakes paints a picture of a planet with significant rainfall or snowmelt.

But planetary scientists who specialize in computer climate models have been unable to reproduce an ancient climate with large amounts of liquid water present for 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,” said study lead author Dr. Gaia Stucky de Quay, a postdoctoral researcher in the Jackson School of Geosciences and the Center for Planetary Systems Habitability at the University of Texas at Austin.

“It had lots of rain or snowmelt to fill those channels and lakes.”

“Now it’s completely dry. We’re trying to understand how much water was there and where did it all go.”

In the study, Dr. Stucky de Quay and colleagues found that precipitation must have been between 4 to 159 m (13-520 feet) in a single episode to fill the Martian lakes and, in some cases, provide enough water to overflow and breach the lake basins.

“Although the range is large, it can be used to help understand which climate models are accurate,” Dr. Stucky de Quay said.

“Climate models have trouble accounting for that amount of liquid water at that time. It’s like, liquid water is not possible, but it happened. This is the knowledge gap that our work is trying to fill in.”

The scientists looked at 96 open-basin and closed-basin lakes and their watersheds, all thought to have formed between 3.5 billion and 4 billion years ago.

Using satellite images and topography, they measured lake and watershed areas, and lake volumes, and accounted for potential evaporation to figure out how much water was needed to fill the lakes.

By looking at ancient closed and open lakes, and the river valleys that fed them, they were able to determine a minimum and maximum precipitation.

In 13 cases, the authors discovered coupled basins — containing one closed and one open basin that were fed by the same river valleys — which offered key evidence of both maximum and minimum precipitation in one single event.

“Our study takes previously identified closed and open lake basins, but applies a clever new approach to constrain how much precipitation these lakes experienced,” said study co-author Dr. Tim Goudge, also from the Jackson School of Geosciences and the Center for Planetary Systems Habitability at the University of Texas at Austin.

“Not only do these results help us to refine our understanding of the ancient Mars climate, but they also will be a great resource for putting results from NASA’s Mars 2020 Perseverance rover into a more global context.”

A paper on the findings was published online in the journal Geology.

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Gaia Stucky de Quay et al. Precipitation and aridity constraints from paleolakes on early Mars. Geology, published online August 13, 2020; doi: 10.1130/G47886.1

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