[meteorite-list] New CU-NASA Research Belies Previous Idea That Mars Was Once Warm, Wet Planet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:53:33 2004
Message-ID: <200212052309.PAA18877_at_zagami.jpl.nasa.gov>

http://www.colorado.edu/NewsServices/NewsReleases/2002/2092.html

Contact:
University of Colorado at Boulder
Teresa Segura, (650) 604- 0321
segurat_at_colorado.edu
Owen B. Toon, (303) 492-1534
toon_at_lasp.colorado.edu
Jim Scott, (303) 492-3114

Dec. 3, 2002

Note Editors: Contents embargoed for use until 2 p.m. EST on Thursday, Dec.
5. The phone number to contact Segura or Toon after Dec. 5 is (415) 905-1007
at AGU.

NEW CU-NASA RESEARCH BELIES PREVIOUS IDEA
THAT MARS WAS ONCE WARM, WET PLANET

A new study led by University of Colorado at Boulder researchers indicates
Mars has been primarily a cold, dry planet following its formation some 4
billion years ago, making the possibility of the evolution of life there
challenging at best.

Led by CU-Boulder doctoral candidate Teresa Segura and her adviser,
Professor Owen B. Toon, the team used Mars photos and computer models to
show that large asteroids or comets hit the planet some 3.5 billion years
ago. These impacts apparently occurred about the time major river channels
were formed on the Red Planet, said Segura.

According to the available evidence, roughly 25 huge impactors, each about
60 miles to 150 miles in diameter, slammed into Mars roughly every 10
million to 20 million years during the period, blowing a volume of debris
equivalent to a global blanket hundreds of yards thick into the atmosphere.
The material is believed to have melted portions of subsurface and polar
ice, creating steam and scalding water that rained back on Mars at some six
feet per year for decades or centuries, causing rivers to form and flow,
according to the study.

But the study belies the warm, wet, Mars theory of rivers and oceans
embraced by many planetary scientists, since such impactors were so
infrequent. "There apparently were some brief warm and wet periods on Mars,
but we believe that through most of its history, Mars has been a cold, dry
planet," said Segura, currently a visiting researcher at NASA-Ames in
California.

A paper by Segura, Toon, CU-Boulder graduate Anthony Colaprete -- now at
NASA-Ames -- and Kevin Zahnle of NASA-Ames, will appear in the Dec. 6 issue
of Science.

"When the river valleys on Mars were confirmed in the 1970s, many scientists
believed there once was an Earth-like period with warmth, rivers and
oceans," said Toon, director of CU-Boulder's Program in Oceanic and
Atmospheric Sciences and a professor at the University's Laboratory for
Astrophysics and Space Physics. "What sparked our interest was that the
large craters and river valleys appeared to be about the same age."

In between such catastrophic events, the planet was likely very cold, dry
and inhospitable to any life forms, said Toon. "We definitely see river
valleys but not tributaries, indicating the rivers were not as mature as
those on Earth."

The rare, hot rains pelting Mars that likely came from water in asteroids
and comets hitting the planets and the evaporation of some ice from polar
caps and ice beneath the impacts would have been spectacular, said Segura.
"We believe these events caused short periods of a warm and wet climate, but
overall, we think Mars has been cold and dry for the majority of its
history."

According to Toon, previous theories that carbon dioxide gas and clouds
warmed Mars during its early history "just have not worked out
quantitatively." There is no evidence on Mars of large limestone deposits
from the first billion years, which would be directly linked to large
amounts of C02, a greenhouse gas, he said.

There also is no evidence that another greenhouse gas, methane -- which can
be created naturally by volcanic eruptions or produced by primitive life --
was present in the Martian atmosphere. But even CO2 and methane combined
would not be enough to warm the planet as greenhouse gases did on Earth and
Venus in their early histories, Toon said.

"Hypotheses of a warm, wet Mars, based on the presumption that the valley
networks formed in a long-lasting greenhouse climate, imply that Mars may
once have been teeming with life," wrote the authors in Science. "In
contrast, we envision a cold and dry planet, an almost endless winter broken
by episodes of scalding rains followed by flash floods.

"Only during the brief years or decades after the impact events would Mars
have been temperate, and only then might it have bloomed with life as we
know it," they wrote. Although temperatures in the subsurface of Martian
soil may have exceeded the boiling point during the impact period and
provided a possible refuge for life underground, the short duration of warm
periods predicted by the researchers would have made it difficult for life
to ever establish itself on Mars, the team concluded.

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Received on Thu 05 Dec 2002 06:09:20 PM PST