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Fwd = New CU-NASA Research Belies Previous Idea That Mars Was Once Warm, Wet

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  • Frits Westra
    Forwarded by: fwestra@hetnet.nl (Frits Westra) Originally from: NASA Jet Propulsion Laboratory Original Subject: New CU-NASA Research
    Message 1 of 1 , Dec 5, 2002
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      Forwarded by: fwestra@... (Frits Westra)
      Originally from: NASA Jet Propulsion Laboratory <info@...>
      Original Subject: New CU-NASA Research Belies Previous Idea That Mars Was Once Warm, Wet Planet
      Original Date: Thu, 5 Dec 2002 17:33:44 -0600

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      University of Colorado at Boulder
      Teresa Segura, (650) 604- 0321
      Owen B. Toon, (303) 492-1534
      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.


      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

      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

      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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