UChicago News
Rivers raged on Mars late into its history
By Louise Lerner <https://news.uchicago.edu/taxonomy/term/49911>
Mar 27, 2019
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UChicago scientists find substantial runoff fed rivers for more than a billion
years
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<http://advances.sciencemag.org/content/5/3/eaav7710>, 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<https://news.uchicago.edu/story/rain-or-snow-likely-formed-martian-rivers>
and climates of other
worlds<https://news.uchicago.edu/story/water-worlds-could-support-life-study-says>.
“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.
“It’s already hard to explain rivers or lakes based on the information we have.
This makes a difficult problem even more difficult.”
—Asst. Prof. Edwin Kite
BR Note: This is one of several photos in the story. The lighter colors show
river valleys
and high concentrations of water in the past. Reminds me of some place like
the US Southwest.
[River in Mars]
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.
But 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.
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.
Citation: “Persistence of intense, climate-driven runoff late in Mars history.”
Kite, et al, Science Advances, March 27, 2019. Doi:
10.1126/sciadv.aav7710<http://advances.sciencemag.org/content/5/3/eaav7710>
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