Rivers raged on Mars late into its history

March 27, 2019

Long ago on Mars, water carved deep riverbeds into the planet's surface--but we still don't know what kind of weather fed them. Scientists aren't sure, because their understanding of the Martian climate billions of years ago remains incomplete.

A new study by University of Chicago scientists catalogued these rivers to conclude that significant river runoff persisted on Mars later into its history than previously thought. According to the study, published March 27 in Science Advances, the runoff was intense--rivers on Mars were wider than those on Earth today--and occurred at hundreds of locations on the red planet.

This complicates the picture for scientists trying to model the ancient Martian climate, said lead study author Edwin Kite, assistant professor of geophysical sciences and an expert in both the history of Mars and climates of other worlds. "It's already hard to explain rivers or lakes based on the information we have," he said. "This makes a difficult problem even more difficult."

But, he said, the constraints could be useful in winnowing the many theories researchers have proposed to explain the climate.

Mars is crisscrossed with the distinctive tracks of long-dead rivers. NASA's spacecraft have taken photos of hundreds of these rivers from orbit, and when the Mars rover Curiosity landed in 2012, it sent back images of pebbles that were rounded--tumbled for a long time in the bottom of a river.

It's a puzzle why ancient Mars had liquid water. Mars has an extremely thin atmosphere today, and early in the planet's history, it was also only receiving a third of the sunlight of present-day Earth, which shouldn't be enough heat to maintain liquid water "Indeed, even on ancient Mars, when it was wet enough for rivers some of the time, the rest of the data looks like Mars was extremely cold and dry most of the time," Kite said.

Seeking a better understanding of Martian precipitation, Kite and his colleagues analyzed photographs and elevation models for more than 200 ancient Martian riverbeds spanning over a billion years. These riverbeds are a rich source of clues about the water running through them and the climate that produced it. For example, the width and steepness of the riverbeds and the size of the gravel tell scientists about the force of the water flow, and the quantity of the gravel constrains the volume of water coming through.

Their analysis shows clear evidence for persistent, strong runoff that occurred well into the last stage of the wet climate, Kite said.

The results provide guidance for those trying to reconstruct the Martian climate, Kite said. For example, the size of the rivers implies the water was flowing continuously, not just at high noon, so climate modelers need to account for a strong greenhouse effect to keep the planet warm enough for average daytime temperatures above the freezing point of water.

The rivers also show strong flow up to the last geological minute before the wet climate dries up. "You would expect them to wane gradually over time, but that's not what we see," Kite said. The rivers get shorter--hundreds of kilometers rather than thousands--but discharge is still strong. "The wettest day of the year is still very wet."

It's possible the climate had a sort of "on/off" switch, Kite speculated, which tipped back and forth between dry and wet cycles.

"Our work answers some existing questions but raises a new one. Which is wrong: the climate models, the atmosphere evolution models, or our basic understanding of inner solar system chronology?" he said.
-end-
UChicago Planetary GIS/Data Specialist David Mayer, now at the United States Geologic Survey Astrogeology Program, and then-visiting student Gaia Stucky de Quay from Imperial College London, co-authored the study, as well as scientists with the Smithsonian Institution, the Natural History Museum in London and the Centre National de la Recherche Scientifique in Paris. The study used University of Chicago Research Computing Center resources.

University of Chicago

Related Mars Articles from Brightsurf:

Water on ancient Mars
A meteorite that originated on Mars billions of years ago reveals details of ancient impact events on the red planet.

Surprise on Mars
NASA's InSight mission provides data from the surface of Mars.

Going nuclear on the moon and Mars
It might sound like science fiction, but scientists are preparing to build colonies on the moon and, eventually, Mars.

Mars: Where mud flows like lava
An international research team including recreated martian conditions in a low-pressure chamber to observe the flow of mud.

What's Mars made of?
Earth-based experiments on iron-sulfur alloys thought to comprise the core of Mars reveal details about the planet's seismic properties for the first time.

The seismicity of Mars
Fifteen months after the successful landing of the NASA InSight mission on Mars, first scientific analyses of ETH Zurich researchers and their partners reveal that the planet is seismically active.

Journey to the center of Mars
While InSight's seismometer has been patiently waiting for the next big marsquake to illuminate its interior and define its crust-mantle-core structure, two scientists, have built a new compositional model for Mars.

Getting mac and cheese to Mars
Washington State University scientists have developed a way to triple the shelf life of ready-to-eat macaroni and cheese, a development that could have benefits for everything from space travel to military use.

Life on Mars?
Researchers from Hungary have discovered embedded organic material in a Martian meteorite found in the late 1970s.

New evidence of deep groundwater on Mars
Researchers at the USC Arid Climate and Water Research Center (AWARE) have published a study that suggests deep groundwater could still be active on Mars and could originate surface streams in some near-equatorial areas on Mars.

Read More: Mars News and Mars Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.