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  • Frits Westra
    Forwarded by: fwestra@hetnet.nl (Frits Westra) URL: http://www.space.com/searchforlife/lifesigns_spots_020103.html Original Date: Thu, 3 Jan
    Message 1 of 1 , Jan 3, 2002
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      Forwarded by: fwestra@... (Frits Westra)
      URL: http://www.space.com/searchforlife/lifesigns_spots_020103.html
      Original Date: Thu, 3 Jan 2002 11:31:47 -0800

      ========================== Forwarded message begins ======================

      Signs of Life: On the Lookout for
      Extraterrestrial Sweet Spots
      By Leonard David
      Senior Space Writer
      posted: 07:00 am ET
      03 January 2002

      BOULDER, COLORADO - Looking for life elsewhere is a tough task for
      human or robot. The good news is that the scientific skill and tools
      to search for, detect and inspect extraterrestrial life are advancing
      rapidly.

      A revolution in the field of microbiology is afoot, along with
      extraordinary progress in understanding the "geobiological" history of
      Earth. And then there's growing amazement about life on this planet
      and how it can survive and thrive even in the most extreme and
      bizarre of environments. For example, within the last ten years
      alone, more than 1,500 new species of microorganisms have been
      discovered and genetically sequenced.

      In a just issued report, Signs of Life, a multidisciplinary group of
      scientists grappled with techniques and technologies to detect
      evidence for extraterrestrial life - either on the spot on other
      worlds, or within prime pickings hauled back to Earth by robotic
      spacecraft.

      Spurred largely by an April 2000 workshop held in Washington, D.C.,
      report findings and conclusions were pulled together by the National
      Research Council (NRC) Committee on the Origins and Evolution of Life.

      "The report is based on a workshop that brought together a healthy
      spectrum of senior experts and young researchers," says Jonathan
      Lunine, co-chair of the committee and professor of planetary science
      and physics at the University of Arizona in Tucson. Many of the
      workshop attendees are developing techniques to detect life, and
      modeling the environments in which such techniques might be used on
      other planets, he explains.

      John Baross, associate professor of oceanography at the University of
      Washington in Seattle, also co-chairs the committee.

      "The discussion was vigorous and exciting. This is a different world
      of life detection than that in 1976, at the time of Viking," Lunine
      told SPACE.com.

      Lunine feels the key to success in life detection in the field is to
      try a range of techniques that vary in their specificity and need for
      prior assumptions about the nature of life. Doing so will maximize the
      chances for success in searches at the planet itself.

      "With returned samples, of course, one should throw everything
      possible at the effort," Lunine explains.

      The Committee on the Origins and Evolution of Life, Lunine adds, is
      continuing its efforts with a study on the potential nature of life
      that might be very different from terrestrial...and how one would go
      about detecting such life.

      Elusive answers

      Since the 1976 landings of two Viking landers on Mars, the
      technological ability to spot life on celestial bodies has made
      impressive strides. Furthermore, understanding the nature of life and
      the concomitant power of analytical tools in the biological sciences
      are viewed together as "one of the most dramatic changes since
      Viking," the NRC report states.

      In coming to grips with the central question of what is life, the
      committee assumed that if life exists on other planets or moons, it
      will be carbon based and dependent on liquid water. Also, it will be
      self-replicating and capable of evolving.

      The quest to find life beyond Earth involves answers to several tough
      questions. For instance, how does one determine if there are living
      organisms in a returned sample? Secondly, can living organisms leave
      tell tale traces from earlier times that can be found in a returned
      sample? Lastly, how does one determine whether there are living
      organisms or fossils in samples examined robotically on another solar
      system body?

      Lessons from the "Mars rock"

      Firm answers to these questions are elusive, reports the study group.
      There are great uncertainties regarding the possible range of
      chemistry and morphology that could constitute life.

      The committee found that "there is a disconnect between those
      techniques that have been developed to an exquisite degree of
      sensitivity to identify terrestrial organisms and those that could
      provide the greatest probability of detecting exotic life forms from
      another planet."

      "Given the extreme difficulty (or impossibility) of inductively
      describing all possible living processes based on terrestrial
      biochemistry, no single approach, or even combination of approaches,
      will guarantee success on a given sample."

      That view has been brought home, quite literally, by the ongoing
      research of the often called "Mars rock" - the infamous ALH84001
      meteorite. The claim of evidence for biological processes in that rock
      of ages from the red planet remains controversial and unresolved.

      ALH84001 offers an important lesson in the fundamental complexity of
      identifying the faint traces of present biology or Martian life that
      is long gone.

      "Perhaps even more difficult, if life or its remains is detected in a
      sample, will be the determination of whether it is a terrestrial
      containment from Earth, and if so, whether it was delivered by the
      spacecraft or in the natural process of cross-contamination via
      asteroidal or cometary impact," the committee report adds.

      Sterile approach

      Dispatching high-tech gear to scout for life -- and not drag along
      hitchhiking terrestrial microorganisms in the process -- is a
      difficult challenge, the committee notes. Spacecraft must be
      sterilized to avoid tainting other planetary bodies with Earth biology
      - a situation tagged as "forward contamination."

      There remains, however, "intense debate", the NRC report observes,
      over the level to which spacecraft sterilization should be achieved
      for missions to particular solar system bodies.

      Firstly, sterilization must be done in such a way as to avoid damaging
      spacecraft components.

      One procedure -- sterilization via dry heating in an oven -- was
      performed on the two Viking landers that searched for life on the red
      planet. However, that approach puts harsh demands on spacecraft
      components and leads to a substantial increase in mission cost and,
      possibly, the chances of mission failure, the report states.

      Sterilization by particle irradiation of a space probe is an
      alternative. Yet this technique may not reach all spacecraft
      subsystems, particularly when the mission design dictates shielding
      electronic components from ambient sources of radiation. That type
      environment, for example, is found in the Jupiter system.

      Another worry is that radiation-tolerant bacteria may dictate that
      irradiation levels exceed even the extraordinary levels to be
      experienced during the prime mission phase of, say, a mission to
      Jupiter's moon, Europa.

      Titan: cold soak

      Regaining access to all parts of a spacecraft before launch to assure
      that sterilization has taken place is an unsolved problem, the
      committee reports.

      Flagged in the report is the very compact Huygens probe now en route
      to Saturn. The lander is to be dropped off on that planet's mysterious
      moon,
      Titan, by the Cassini interplanetary spacecraft after arrival
      in 2004.

      The European Space Agency-built probe was not sterilized to a high
      standard on the grounds that the profoundly cold Titan environment
      would sterilize the lander soon after landing. "Yet Titan is itself a
      target for investigating advanced stages of organic chemistry that on
      Earth might have led to life," the report notes.

      In the area of spacecraft cleanliness, the committee encourages
      further work to refine sterilization approaches, with an eye toward
      minimizing impacts on spacecraft cost and mission success.

      Hauling back the goods

      Another hotly debated topic is that of back contamination, whereby
      extraterrestrial samples brought back might harm biological processes
      here on Earth.

      At issue is whether organisms "out there" might exist that are
      sufficiently different from terrestrial organisms "down here" to
      escape laboratory detection, yet similar enough to pose a threat to
      the health of our biosphere.

      "In the debates about life detection and back contamination, this
      'niche' has not been explored to the extent that it should be - in
      part because of the difficulties in answering the question," the
      committee report states.

      The committee recommends that a focused study be done in the near
      future to address the detection of microorganisms with varying degrees
      of nonterrestrial biochemistry, and the possible threat that such
      organisms might pose to terrestrial organisms.

      Similar in view from past studies on back contamination, the committee
      report states that there are practical and societal reasons for
      ensuring planetary protection for all interplanetary missions.

      "Although the probability that an extraterrestrial life form could be
      pathogenic to humans, or even viable at all in the terrestrial
      environment, is very low, it cannot be shown to be zero," the report
      says.

      Back in the lab

      Due to the myriad of technical woes to overcome in returning samples
      back to Earth, much of the search for life elsewhere may initially be
      done "in situ", that is, on the spot, by robots.

      One problem.

      Many of the powerful and sensitive techniques for detecting life in
      laboratories here on Earth are not yet "space rated". That is, they
      are far too big, complex, and not ready for prime time flight. That
      condition may remain so, at least in the near future.

      Because of the continuing rapid improvements in technology, the
      committee reports, it is not appropriate to recommend a specific set
      of techniques for in situ life detection at this time. Pressing on
      with the design of innovative and "miniaturizable" techniques for in
      situ life detection is encouraged.

      It is an almost certainly that the most interesting locales from the
      point of view of the search for life will not be the easiest to get
      to. Finding those comfy niches that could be just right for life
      today, or were in the past, suggests the committee, is likely to mean
      landing in less-than-totally-safe sites.

      "It remains unclear as to which environments in our solar system
      should be searched for signs of life," the committee found, beyond the
      general identification of planetary targets - such as Mars, Europa,
      and Titan. "In large measure, we yet do not known enough about these
      bodies to target searches in particular locations."

      Picking those extraterrestrial sweet spots will require a series of
      missions, including orbital reconnaissance, followed by
      up-close-and-personal perusals using landed vehicles.
      _________________________________________________________________

      �1999 - 2002 SPACE.com, inc. ALL RIGHTS RESERVED.

      ========================== Forwarded message ends ========================
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