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Detectability of Extraterrestrial Technological Activities

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Author Topic: Detectability of Extraterrestrial Technological Activities  (Read 339 times)
Jennifer Murdoch
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« Reply #30 on: February 04, 2010, 01:24:40 pm »

for interstellar communications  have been performed by Betz (1986),
       Kingsley (1992), Ross (1980), and Rather (1991).

       The first international  SETI  in   the   Optical  Spectrum  (OSETI)
       Conference was organized by Stuart Kingsley, under  the  sponsorship
       of The International   Society   for  Optical  Engineering,  at  Los
       Angeles, California, in January of 1993.

       There have also been independent suggestions by Drake and Shklovskii
       (Sagan and Shklovskii,  1966)  that  the  presence  of  a  technical
       civilization could be  announced  by  the dumping of  a  short-lived
       isotope, one which  would  not  ordinarily  be expected in the local
       stellar spectrum, into the atmosphere of a star.  Drake suggested an
       atom with a  strong, resonant absorption  line,  which  may  scatter
       about 10exp8 photons  sec  -1  in  the stellar radiation  field.   A
       photon at optical  frequencies has an energy of about 10exp(-12) erg
       or 0.6 eV, so each atom will scatter  about  10exp(-4)  erg sec-1 in
       the resonance line.  If we consider that the typical  spectral  line
       width might be  about  1  ^O,  and  if  we assume that a ten percent
       absorption will be  detectable, then  this  "artificial  smog"  will
       scatter about (1A/5000A)x10exp(-1)  =  2x10exp(-5)   of   the  total
       stellar flux.

       Sagan and Shklovskii  (1966) considered that if the central star has
       a typical solar flux of 4x10exp33  erg  sec-1, it must scatter about
       8x10exp28 erg sec-1  for  the line to be detected.   Thus,  the  ETC
       would need (8x10exp28)/10exp(-4)  =  8x10exp32 atoms.  The weight of
       the hydrogen atom (mH) is 1.66x10exp(-24)  g,  so  the  weight of an
       atom of atomic weight n is nxmH grams.
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Jennifer Murdoch
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« Reply #31 on: February 04, 2010, 01:24:55 pm »

Drake proposed the used of Technetium (Tc) for this  purpose.   This
       element is not  found  on  Earth  and  its presence is observed very
       weakly in the Sun, in part because  it  is  short-lived.   Tc's most
       stable form decays  radioactively  within  an  average   of   twenty
       thousand years.  Thus,  for  the  case  of Tc, we need to distribute
       some 1.3x10exp11 grams, or 1.3x10exp5 tons, of this element into the
       stellar spectrum.  However, technetium  lines have not been found in
       stars of solar spectral type, but rather only in peculiar ones known
       as S stars.   We  must know more than we do about  both  normal  and
       peculiar stellar spectra  before we can reasonably conclude that the
       presence of an unusual atom in an  stellar  spectrum  is  a  sign of
       extraterrestrial intelligence.

       Whitmire and Wright  (1980)  considered  the possible  observational
       consequences of galactic  civilizations  which  utilize  their local
       star as a repository for radioactive  fissile  waste material.  If a
       relatively small fraction  of  the nuclear sources  present  in  the
       crust of a   terrestrial-type  planet  were  processed  via  breeder
       reactors, the resulting  stellar   spectrum   would  be  selectively
       modified over geological time periods, provided that  the star has a
       sufficiently shallow outer  convective  zone.   They  have estimated
       that the abundance anomalies resulting from the slow neutron fission
       of plutonium-239 and uranium-233 could  be duplicated (compared with
       the natural nucleosynthesis processes), if this process takes place.
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Jennifer Murdoch
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« Reply #32 on: February 04, 2010, 01:25:06 pm »

Since there are no known natural nucleosynthesis mechanisms that can
       qualitatively duplicate the   asymptotic  fission  abundances,   the
       predicted observational characteristics   (if  observed)  could  not
       easily be interpreted as a natural phenomenon.  They have suggested

                                      Page 11





       making a survey of A5-F2 stars for (1) an anomalous overabundance of
       the elements of praseodymium and neodymium, (2) the presence, at any
       level, of technetium or plutonium, and (3) an anomalously high ratio
       of barium to   zirconium.    Of  course,  if  a  candidate  star  is
       identified, a more detailed spectral analysis could be performed and
       compared with the predicted ratios.

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Jennifer Murdoch
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« Reply #33 on: February 04, 2010, 01:25:21 pm »

Following the same  kind  of  ideas,   Philip   Morrison   discussed
       (Sullivan, 1964) converting one's sun into a signaling light by
       placing a cloud of particles in orbit around it.   The  cloud  would
       cut enough light  to  make  the  sun appear to be flashing when seen
       from a distance, so long as the viewer was close to the plane of the
       cloud orbit.  Particles about one  micron in size, he thought, would
       be comparatively resistant  to disruption.  The mass  of  the  cloud
       would be comparable  to  that of a comet covering an area of the sky
       five degrees wide, as seen from  the  sun.   Every  few  months, the
       cloud would be shifted to constitute a slow form of  signaling,  the
       changes perhaps designed to represent algebraic equations.

       Reeves (1985) speculated  on  the  origin of mysterious stars called
       blue stragglers.  This class of star was first identified by Sandage
       (1952).  Since that time, no clear  consensus upon their origins has
       emerged.  This is  not,  however,  due to a paucity  of  theoretical
       models being devised.   Indeed,  a  wealth of explanations have been
       presented to explain the origins of  this star class.  The essential
       characteristic of the blue stragglers is that they  lie on, or near,
       the Main Sequence,  but  at  surface  temperatures  and luminosities
       higher than those stars which define the cluster turnoff.
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Jennifer Murdoch
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« Reply #34 on: February 04, 2010, 01:25:41 pm »

Reeves (1985) suggested the intervention  of  the  inhabitants  that
       depend on these  stars  for  light and heat.  According  to  Reeves,
       these inhabitants could  have  found  a  way  of keeping the stellar
       cores well-mixed with hydrogen,  thus  delaying  the  Main  Sequence
       turn-off and the ultimately destructive, red giant phase.

       Beech (1990) made a more detailed analysis of Reeves' hypothesis and
       suggested an interesting  list  of  mechanisms for  mixing  envelope
       material into the core of the star.  Some of them are as follows:

         o  Creating a "hot spot" between the stellar core and surface
            through the detonation of a series of hydrogen bombs.  This
            process may alternately be achieved by aiming "a powerful,
            extremely concentrated laser beam" at the stellar surface.

         o  Enhanced stellar rotation and/or enhanced magnetic fields.
            Abt (1985) suggested from his studies of blue stragglers that
            meridional mixing in rapidly rotating stars may enhance their
            Main Sequence lifetime.

       If some of  these  processes  can  be  achieved,  the  Main Sequence
       lifetime may be greatly extended by  factors  of ten or more.  It is
       far too early to establish, however, whether all the blue stragglers
       are the result of astroengineering activities.

       Editor's Note:  References to this paper will be published in Part 2
                       in the January 1994 issue of the EJASA.




                                      Page 12


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Jennifer Murdoch
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« Reply #35 on: February 04, 2010, 01:25:54 pm »

       Related EJASA Articles -

         "Does Extraterrestrial Life Exist?", by Angie Feazel
          - November 1989

         "Suggestions for an Intragalactic Information Exchange System",
          by Lars W. Holm - November 1989

         "Radio Astronomy: A Historical Perspective",
          by David J.  Babulski - February 1990

         "Getting Started in Amateur Radio Astronomy",
          by Jeffrey M.  Lichtman - February 1990

         "A Comparison of Optical and Radio Astronomy",
          by David J.  Babulski - June 1990

         "The Search   for  Extraterrestrial  Intelligence  (SETI)  in  the
          Optical Spectrum, Parts A-F",
          by Dr. Stuart A. Kingsley - January 1992

         "History of the Ohio SETI Program", by Robert S. Dixon
          - June 1992

         "New Ears on the Sky: The NASA SETI Microwave Observing Project",
          by Bob Arnold, the ARC, and JPL SETI Project - July 1992

         "First International Conference on Optical SETI",
          by Dr.  Stuart A.  Kingsley - October 1992

         "Conference Preview: The Search for Extraterrestrial Intelligence
          (SETI) in the Optical Spectrum",
          by Dr. Stuart A. Kingsley - January 1993

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Jennifer Murdoch
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« Reply #36 on: February 04, 2010, 01:26:08 pm »

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