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Venus inferno due to 'runaway greenhouse effect', say scientists

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  • mtneuman@juno.com
    by Staff Writers Paris (AFP) Nov 28, 2007 Once styled as Earth s twin, Venus was transformed from a haven for water to a fiery hell by an unstoppable
    Message 1 of 1 , Nov 28, 2007
      by Staff Writers
      Paris (AFP) Nov 28, 2007
      Once styled as Earth's twin, Venus was transformed from a haven for water
      to a fiery hell by an unstoppable greenhouse effect, according to an
      investigation by the first space probe to visit our closest neighbour in
      more than a decade.
      Like peas in a cosmic pod, the second and third rocks from the Sun came
      into being 4.5 billion years ago with nearly the same radius, mass,
      density and chemical composition.

      But only one, Earth, developed an atmosphere conducive to life. The
      other, named with unwitting irony after the Roman goddess of love, is an
      inferno of carbon dioxide (CO2), its bone-dry surface hot enough to melt
      lead or zinc.

      The European Space Agency's (ESA) Venus Express, orbiting its prey since
      April 2006, seeks to explain this astonishing divergence.

      Preliminary data from the probe reveal a Venus that is more Earth-like
      than once thought -- but not in ways that are reassuring.

      "The basic physics of the greenhouse effect are the same on Venus as on
      Earth," said Venus Express scientist David Grinspoon. "Perhaps the same
      fate will await the water on Earth."

      At first blush, the two worlds, 42 million kilometres (26 million miles)
      apart at their closest points, could hardly be more different.
      Venus inferno due to 'runaway greenhouse effect', say scientists
      by Staff Writers
      Paris (AFP) Nov 28, 2007

      Earth's temperature range has remained largely stable and its atmosphere
      has maintained a balance of gases -- and this, with the precious water
      covering two-thirds of its surface, has allowed riotous biodiversity to

      Venus' atmosphere, though, overwhelming comprises suffocating CO2 and a
      permanent blanket of clouds laced with sulphuric acid. Oxygen is nowhere
      to be found, nor is any water except in atmospheric traces.

      Its surface hovers at 457 degrees Celsius (855 degrees Fahrenheit) and
      has a pressure equivalent, on Earth, to being a kilometer (3,250 feet)
      under the sea.

      But this was not always so, says Hakan Svedhem, an ESA scientist and lead
      author of one of eight studies published on Wednesday in the British
      journal Nature.

      Venus, he believes, was partially covered with water before it became
      doomed by global warming.

      "Probably because Venus was closer to the Sun, the atmosphere was a
      little bit warmer and you got more water very high up," he told AFP.

      As water vapour is a greenhouse gas, this further trapped solar heat,
      causing the planet to heat up even more. So more surface water
      evaporated, and eventually dissipated into space.

      It was a "positive feedback" -- a vicious circle of self-reinforcing
      warming which slowly dessicated the planet.

      "Eventually the oceans begin to boil," said Grinspoon. "We believe this
      is what happened on Venus."

      Even today, Earth and Venus have roughly the same amount of CO2. But
      whereas most of Earth's store remains locked up in the soil, rocks and
      oceans, on Venus the extreme heat pushed the gas into the air.

      "You wound up with what we call a runaway greenhouse effect," Svedhem
      told AFP in an interview. "(It) reminds us of pressing problems caused by
      similar physics on Earth."

      Venus Express, the first dedicated mission since the US Magellan Orbiter
      mapped the planet's surface in the early 1990s, is equipped with an
      arsenal of sensors to peer through the dense clouds across the entire
      light spectrum.

      One surprise already turned up by the 600-kilo (1,320-pound) probe is a
      30-40 C (55-70 F) variation between daytime and nighttime temperatures at
      an altitude of 60 kilometres (40 miles).

      At this height, violent winds three times stronger than hurricanes on
      Earth should even out differences, or so it had been thought.

      There are many questions yet to be answered during the mission, which is
      scheduled to last through 2013.

      One is whether there is lightning on Venus. Given the kind of clouds
      covering the planet, there simply should not be any, Andrew Ingersoll, a
      professor at Caltech University in Pasadena, California, said in a
      commentary, also published in Nature.

      But Venus Express has detected "whistlers," low-frequency electromagnetic
      waves that last a fraction of a second and are normally a sure sign of
      electrical discharges.

      "We consider this to be the first definitive evidence of abundant
      lightning on Venus," said Grinspoon. A powerful source of energy,
      lightning changes the chemistry of any planet with a dynamic atmosphere,
      such as Earth or Venus, he added.

      Another enigma: sometime within the last 700 to 900 million years, the
      planet seems to have lost its skin, its topography resculpted by some
      giant force.

      "Venus has quite recently completely changed its surface," said Svedhem.
      "Some event completely changed everything -- this is a strange process we
      do not completely understand."
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