By revealing how much precipitation and snowmelt filled its lake beds and river basins 3.5 billion to 4 billion years ago, a recent study from The University of Texas at Austin is assisting scientists in reconstructing the ancient climate of Mars.
The Mars 2020 Perseverance rover is traveling to the red planet to land in one of the lake beds that are essential to this new research, and the study, which was published in Geology, marks the first time that researchers have quantified the precipitation that must have been present across the planet.
Scientists are rather perplexed by the old Mars environment. Geologists believe that ancient lake basins and riverbeds indicate a planet that saw major snowmelt or rainfall.
However, experts in computerized climate models of the planet’s climate have not been able to recreate an ancient climate with significant volumes of liquid water present for an extended period of time to explain the observed geology.
“This is extremely important because 3.5 to 4 billion years ago Mars was covered with water. It had lots of rain or snowmelt to fill those channels and lakes,” said lead author Gaia Stucky de Quay, a postdoctoral fellow at UT’s Jackson School of Geosciences. “Now it’s completely dry. We’re trying to understand how much water was there and where did it all go.”
Despite the fact that there is a lot of frozen water present on Mars, there is now very little liquid water there.
Gaia’s study takes previously identified closed and open lake basins, but applies a clever new approach to constrain how much precipitation these lakes experienced. 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 the Mars 2020 Perseverance Rover into a more global context.
Tim Goudge
In their investigation, researchers discovered that for the lakes to be filled and, in some circumstances, to have enough water to overflow and breach the lake basins, precipitation had to be between 13 and 520 feet (4 to 159 meters) in height in a single occurrence.
Although the range is large, it can be used to help understand which climate models are accurate, Stucky de Quay said.
“It’s a huge cognitive dissonance,” she 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 researchers examined 96 lakes with watersheds that were considered to have originated between 3.5 billion and 4 billion years ago, including both open-basin and closed-basin lakes. Closed lakes are undamaged, whereas open lakes have been torn by overflowing water.
They calculated the amount of water required to fill the lakes by measuring the areas and volumes of lakes and watersheds, taking into account probable evaporation, and using satellite pictures and topography.
The team was able to calculate a minimum and maximum precipitation by examining historical closed and open lakes, as well as the river valleys that supplied them. The dried-up lakes give an idea of how much water may have fallen in a single occurrence without exceeding the lake basin’s wall.
The open lakes depict the bare minimum of water necessary to fill the lake basin to the point where it ruptures and gushes out one side.
Researchers found connected basins in 13 instances that contained one closed and one open basin supplied by the same river valleys, providing crucial evidence of both the maximum and lowest precipitation in a single event.
Another great unknown is how long the rainfall or snowmelt episode must have lasted: days, years, or thousands of years. That’s the next step of the research, Stucky de Quay said.
As this research is published, NASA recently launched Mars 2020 Perseverance Rover to visit Jezero crater, which contains one of the open lake beds used in the study.
Co-author Tim Goudge, an assistant professor in the UT Jackson School Department of Geological Sciences, was the lead scientific advocate for the landing site. He said the data collected by the crater could be significant for determining how much water was on Mars and whether there are signs of past life.
“Gaia’s study takes previously identified closed and open lake basins, but applies a clever new approach to constrain how much precipitation these lakes experienced,” Goudge said. “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 the Mars 2020 Perseverance Rover into a more global context.”
This study was supported by a grant through NASA’s Mars Data Analysis Program.
