[meteorite-list] Valley Networks on Mars Formed During Long Periods of Episodic Flooding, Study Finds

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 11 Sep 2008 17:04:38 -0700 (PDT)
Message-ID: <200809120004.RAA10504_at_zagami.jpl.nasa.gov>


Valley networks on Mars formed during long period of episodic
flooding, study finds

By Tim Stephens (831) 459-2495; stephens at ucsc.edu
University of California-Santa Cruz
September 8, 2008

A new study suggests that ancient features on the surface of Mars called
valley networks were carved by recurrent floods during a long period
when the martian climate may have been much like that of some arid or
semiarid regions on Earth. An alternative theory that the valleys were
carved by catastrophic flooding over a relatively short time is not
supported by the new results.

Often cited as evidence that Mars once had a warm environment with
liquid water on the surface, valley networks are distinctive features of
the martian landscape. In the new study, researchers used sophisticated
computer models to simulate the processes that formed these features.

"Our results argue for liquid water being stable at the surface of Mars
for prolonged periods in the past," said Charles Barnhart, a graduate
student in Earth and planetary sciences at the University of California,
Santa Cruz.

Barnhart conducted the study as a Graduate Student Research Program
scholar at NASA Ames Research Center, working with NASA planetary
scientist Jeffrey Moore and Alan Howard of the University of Virginia. A
paper describing their findings has been accepted for publication in the
Journal of Geophysical Research--Planets and is currently available online.

"For several decades, scientists worked to determine whether or not
there had ever been precipitation on Mars. Only in the last 10 years has
NASA acquired high-resolution topographic data that cinched the case for
massive ancient erosion from precipitation and runoff," Moore said.

Scientists estimate that the valley networks on Mars were carved out
more than 3.5 billion years ago. Studies based on climate models have
suggested that catastrophic events such as asteroid impacts could have
created warm, wet conditions on Mars, causing massive deluges and
flooding for periods of hundreds to thousands of years.

But the new study shows that those conditions would result in features
not seen in the martian landscape, because water would accumulate inside
craters and overflow, carving exit breaches that cut through the crater
walls, Barnhart said.

"Our research finds that these catastrophic anomalies would be so humid
and wet there would be breaching of the craters, which we don't see on
Mars," he said. "The precipitation needs to be seasonal or periodic, so
that there are periods of evaporation and infiltration. Otherwise the
craters overflow."

The researchers used a landform evolution model to simulate how the
surface of Mars would evolve under different climate conditions. They
ran more than 70 simulations under varied conditions and performed
statistical analyses to determine which yielded the best match to the
observed topography of martian valleys.

The results suggest that valley networks formed on Mars during a
semiarid to arid climate that persisted for tens of thousands to
hundreds of thousands of years. Episodic flooding alternated with long
dry periods when water could evaporate or soak into the ground. Rainfall
may have been seasonal, or wet intervals may have occurred over longer
cycles. But conditions that allowed for the presence of liquid water on
the surface of Mars must have lasted for at least 10,000 years, Barnhart

"Precipitation on Mars lasted a long time--it wasn't a brief interval of
massive deluges," he said.


Note to reporters: You may contact Barnhart at (831) 459-1784 or
barnhart at es.ucsc.edu.


Received on Thu 11 Sep 2008 08:04:38 PM PDT

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