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Detectability of Extraterrestrial Technological Activities
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Detectability of Extraterrestrial Technological Activities
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Topic: Detectability of Extraterrestrial Technological Activities (Read 1565 times)
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
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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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
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
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
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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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
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
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
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
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
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
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #36
on:
February 04, 2010, 01:26:08 pm »
==================================================================
Guillermo A. Lemarchand
Universidad de Buenos Aires
POSTAL ADDRESS: C.C.8 - Suc.25,
1425-Buenos Aires,
ARGENTINA
E-MAIL:
lemar@seti.edu.ar
PHONE: 54-1-774-0667 FAX: 54-1-786-8114
==================================================================
THE ELECTRONIC JOURNAL OF THE ASTRONOMICAL SOCIETY OF THE ATLANTIC
December 1993 - Vol. 5, No. 5
Copyright (c) 1993 - ASA
--------------------------------------------------------------------
If you have comments or other information relating to such topics
as this paper covers, please upload to KeelyNet or send to the
Vangard Sciences address as listed on the first page.
Thank you for your consideration, interest and support.
Jerry W. Decker.........Ron Barker...........Chuck Henderson
Vangard Sciences/KeelyNet
--------------------------------------------------------------------
If we can be of service, you may contact
Jerry at (214) 324-8741 or Ron at (214) 242-9346
--------------------------------------------------------------------
Page 13
--------------------------------------------------------------------------------
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