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                           THE ELECTRONIC JOURNAL OF
                   THE ASTRONOMICAL SOCIETY OF THE ATLANTIC

                      Volume 5, Number 5 - December 1993

                         ###########################

                              TABLE OF CONTENTS

                         ###########################

          * ASA Membership and Article Submission Information

          * Detectability of Extraterrestrial Technological Activities,
             Part 1 - Guillermo A. Lemarchand

                         ###########################

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          DETECTABILITY OF EXTRATERRESTRIAL TECHNOLOGICAL ACTIVITIES    

                           Guillermo A. Lemarchand [1]

                  Center for Radiophysics and Space Research
                  Cornell University, Ithaca, New York, 14853

      ==================================================================
      1 - Visiting Fellow under ICSC World Laboratory scholarship. 
      Present address:  University of Buenos Aires, C.C.8-Suc.25, 1425-
      Buenos Aires, Argentina
      ==================================================================

      ==================================================================
                   This paper was originally presented at the
              Second United Nations/European Space Agency Workshop
                             on Basic Space Science

        Co-organized by The Planetary Society in cooperation with the
         Governments of Costa Rica and Colombia, 2-13 November 1992,   
                   San Jose, Costa Rica - Bogota, Colombia

      ==================================================================

        Introduction

        If we want to find evidence for the existence of extraterrestrial
    civilizations (ETC), we must work out an observational strategy for
    detecting this evidence in order to establish the various physical
    quantities in which it involves.  This information must be carefully
    analyzed so that it is neither over-interpreted nor overlooked and 
    can be checked by independent researchers. 

        The physical laws that govern the Universe are the same
    everywhere, so we can use our knowledge of these laws to search for
    evidence that would finally lead us to an ETC.  In general, the
    experimentalist studies a system by imposing constraints and observing
    the system's response to a controlled stimulus.  The variety of these
    constraints and stimuli may be extended at will, and experiments can
    become arbitrarily complex.  In the problem of the Search for
    Extraterrestrial Intelligence (SETI), as well as in conventional
    astronomy, the mean distances are so huge that the "researcher" can
    only observe what is received.  He or she is entirely dependent on the
    carriers of information that transmit to him or her all he or she may
    learn about the Universe. 

        Information carriers, however, are not infinite in variety.
    All information we currently have about the Universe beyond our 
    solar system has been transmitted to us by means of electromagnetic
    radiation (radio, infrared, optical, ultraviolet, X-rays, and gamma
    rays), cosmic ray particles (electrons and atomic nuclei), and more
    recently by neutrinos.  There is another possible physical carrier,
    gravitational waves, but they are extremely difficult to detect. 

        For the long future of humanity, there have also been specula-
    tions about interstellar automatic probes that could be sent for the
    detection of extrasolar life forms around the nearby stars.  Another
    set of possibilities could be the detection of extraterrestrial
    artifacts in our solar system, left here by alien intelligences that
    want to reveal their visits to us. 

        Table 1 summarizes the possible "information carriers" that 
    may let us find the evidence of an extraterrestrial civilization,
    according to our knowledge of the laws of physics.  The classification
    of techniques in Table 1 is not intended to be complete in all respects.  
    Thus, only a few fundamental particles have been listed.  No attempt 
    has been made to include any antiparticles.  This classification, like 
    any such scheme, is also quite arbitrary.  Groupings could be made 
    into different "astronomies". 

                        TABLE 1: Information Carriers

                                 |-
                                 | Radio Waves
                                 | Infrared Rays
               |-                | Optical Rays
               | Photon Astronomy| Ultraviolet Rays
               |                 | X-Rays
    Boson      |                 | Gamma Rays
    Astronomy  |                 |-
               | Graviton Astronomy: Gravity Waves
               |-                     |-
                                      | Neutrinos
             |-           |-  Fermions| Electrons   |-
             | Atomic     |           | Protons     | Cosmic
             | Microscopic|           |-            | Rays
             | Particles  |   Heavy Particles       |-
   Particle  |            |-
   Astronomy |                      |-
             | Macroscopic Particles|       Meteors, meteorites,
             | or objects           |       meteoritic dust
             |-                     |-
                 |-
                 | Space Probes
    Direct       | Manned Exploration
    Techniques   | ET Astroengineering Activities in the Solar System
                 |-

        The methods of collecting this information as it arrives at the
    planet Earth make it immediately obvious that it is impossible to gather
    all of it and measure all its components.  Each observation technique
    acts as an information filter.  Only a fraction (usually small) of the
    complete information can be gathered.  The diversity of these filters
    is considerable.  They strongly depend on the available technology at
    the time. 

        In this paper a review of the advantages and disadvantages of each
    "physical carrier" is examined, including the case that the possible
    ETCs are using them for interstellar communication purposes, as well
    as the possibility of detection activities of extraterrestrial
    technologies. 

        Classification of Extraterrestrial Civilizations

        The analysis of the use of each information carrier are deeply
    connected with the assumption of the level of technology of the other
    civilization. 

        Kardashev (1964) established a general criteria regarding the
    types of activities of extraterrestrial civilizations which can be
    detected at the present level of development.  The most general
    parameters of these activities are apparently ultra-powerful energy
    sources, harnessing of enormous solid masses, and the transmission 
    of large quantities of information of different kinds through space.  
    According to Kardashev, the first two parameters are a prerequisite 
    for any activity of a supercivilization.  In this way, he suggested the 
    following classification of energetically extravagant civilizations: 

        TYPE I:  A level "near" contemporary terrestrial civilization
                 with an energy capability equivalent to the solar 
                 insolation on Earth, between 10exp16 and 10exp17 Watts. 

        TYPE II:  A civilization capable of utilizing and channeling the
                  entire radiation output of its star.  The energy 
                  utilization would then be comparable to the luminosity 
                  of our Sun, about 4x1026 Watts. 

        TYPE III:  A civilization with access to the power comparable
                   to the luminosity of the entire Milky Way galaxy, 
                   about 4x10exp37 Watts. 

        Kardashev also examined the possibilities in cosmic communica-
    tion which attend the investment of most of the available power into
    communication.  A Type II civilization could transmit the contents of
    one hundred thousand average-sized books across the galaxy, a distance
    of one hundred thousand light years, in a total transmitting time
    of one hundred seconds.  The transmission of the same information
    intended for a target ten million light years distant, a typical
    intergalactic distance, would take a transmission time of a few weeks.
    A Type III civilization could transmit the same information over a
    distance of ten billion light years, approximately the radius of the
    observable Universe, with a transmission time of just three seconds. 

        Kardashev and Zhuravlev (1992) considered that the highest level
    of development corresponds to the highest level of utilization of
    solid space structures and the highest level of energy consumption. 
    For this assumption, they considered the temperature of solid space
    structures in the range 3 Kelvin s T s 300 K, the consumption of energy 
    in the range 1 Luminosity (Sun) s L s 10exp12 L(Sun), structures with 
    sizes up to 100 kiloparsecs (kpc), and distances up to Dw 1000 mega-
    parsecs (mpc).  One parsec equals 3.26 light years. 

        Searching for these structures is the domain of millimeter wave
    astronomy.  For the 300 Kelvin technology, the maximum emission 
    occurs in the infrared region (15-20 micrometers) and searching is
    accomplished with infrared observations from Earth and space.  The
    existing radio surveys of the sky (lambda = 6 centimeters (cm) on the
    ground and lambda = 3 millimeters (mm) for the Cosmic Background
    Explorer (COBE) satellite) place an essential limit on the abundance
    of ETC 3 Kelvin technology.  The analyzes of the Infrared Astronomical
    Satellite (IRAS) catalog of infrared sources sets limitations on the
    abundance of 300 Kelvin technology. 

        Information Carriers and the Manifestations of Advanced 
        Technological Civilizations

        Boson and Photon Astronomy

        Electromagnetic radiation carries virtually all the information on
    which modern astrophysics is built.  The production of electromagnetic
    radiation is directly related to the physical conditions prevailing 
    in the emitter.  The propagation of the information carried by
    electromagnetic waves (photons) is affected by the conditions along
    its path.  The trajectories it follows depend on the local curvature
    of the Universe, and thus on the local distribution of matter
    (gravitational lenses), extinction affecting different wavelengths
    unequally, neutral hydrogen absorbing all radiation below the Lyman
    limit (91.3 mm), and absorption and scattering by interstellar dust,
    which is more severe at short wavelengths. 

        Interstellar plasma absorbs radio wavelengths of kilometers and
    above, while the scintillations caused by them become a very important
    effect for the case of ETC radio messages (Cordes and Lazio, 1991). 
    The inverse Compton effect lifts low-energy photons to high energies
    in collisions with relativistic electrons, while gamma and X-ray
    photons lose energy by the direct Compton effect.  The radiation
    reaching the observer thus bears the imprint of both the source and 
    the accidents of its passage though space. 

        The Universe observable with electromagnetic radiation is five-
    dimensional.  Within this phase, four dimensions - frequency coverage 
    plus spatial, spectral, and temporal resolutions - should properly be 
    measured logarithmically with each unit corresponding to one decade 
    (Tarter, 1984).  The fifth dimension is polarization, which has four 
    possible states:  Circular, linear, elliptical, and unpolarized.
    This increases the volume of logarithmic phase space fourfold. 

        It is useful to attempt to estimate the volume of the search space
    which may need to be explored to detect an ETC signal.  For the case
    of electromagnetic waves, we have a "Cosmic Haystack" with an eight-
    dimensional phase space.  Three spatial dimensions (coordinates of the 
    source), one dimension for the frequency of emission, two dimensions 
    for the polarization, one temporal dimension to synchronize trans-
    missions with receptions, and one dimension for the sensitivity of 
    the receiver or the transmission power. 

        If we consider only the microwave region of the spectrum (300
    megahertz (MHz) to 300 gigahertz (GHz)), it is easy to show that this
    Cosmic Haystack has roughly 10exp29 cells, each of 0.1 Hz bandwidth,
    per the number of directions in the sky in which an Arecibo (305-
    meter) radio telescope would need to be pointed to conduct an all-sky
    survey, per a sensitivity between 10exp(-20) and 10exp(-30) [W m-2],
    per two polarizations.  The temporal dimension (synchronization
    between transmission and reception) was not considered in the
    calculation.  The number of cells increase dramatically if we expand
    our search to other regions of the electromagnetic spectrum.  Until
    now, only a small fraction of the whole Haystack has been explored 
    (w 10exp(-15) - 10exp(-16)). 

        TABLE 2: Characteristics of the Electromagnetic Spectrum

          (All the numbers that follows each 10 are exponents.)       
    ==================================================================
    Spectrum      Frequency          Wavelength        Minimum Energy
    Region        Region [Hz]        Region [m]        per photon [eV]
    ==================================================================
    Radio         3x106-3x1010       100-0.01          10-8 - 10-6 
    Millimeter    3x1010-3x1012      0.01-10-4         10-6 - 10-4 
    Infrared      3x1012-3x1014      10-4-10-6         10-4 - 10-2 
    Optical       3x1014-1015        10-6-3x10-7       10-2 - 5 
    Ultraviolet   1015-3x1016        3x10-7-10-8       5 - 102
    X-rays        3x1016-3x1019      10-8-10-11        102 - 105
    Gamma-rays    r3x1019            s10-11            r105         
    ==================================================================

        Radio Waves

        In the last thirty years, most of the SETI projects have been
    developed in the radio region of the electromagnetic spectrum.  A
    complete description of the techniques that all the present and
    near-future SETI programs are using for detecting extraterrestrial
    intelligence radio beacons can be found elsewhere (e.g., Horowitz and
    Sagan, 1993).  The general hypothesis for this kind of search is that
    there are several civilizations in the galaxy that are transmitting
    omnidirectional radio signals (civilization Type II), or that these
    civilizations are beaming these kind of messages to Earth.  In this
    section we will discuss only the detectability of extraterrestrial
    technological manifestations in the radio spectrum. 

        Domestic Radio Signals

        Sullivan et al (1978) and Sullivan (1981) considered the
    possibility of eavesdropping on radio emissions inadvertently
    "leaking" from other technical civilizations.  To better understand
    the information which might be derived from radio leakage, the case of
    our planet Earth was analyzed.  As an example, they showed that the
    United States Naval Space Surveillance System (Breetz, 1968) has an
    effective radiated power of 1.4x10exp (10) watts into a bandwidth of
    only 0.1 Hz.  Its beam is such that any eavesdropper in the declination 
    range of zero to 33 degrees (28 percent of the sky) will be illuminated 
    daily for a period of roughly seven seconds.  This radar has a detecta-
    bility range of leaking terrestrial signals to sixty light years for 
    an Arecibo-type (305-meter) antenna at the receiving end, or six
    hundred light years for a Cyclops array (one thousand dishes of 100-
    meter size each). 

        Recently Billingham and Tarter (1992) estimated the maximum range
    at which radar signals from Earth could be detected by a search similar 
    to the NASA High Resolution Microwave Survey (HRMS) assumed to be 
    operating somewhere in the Milky Way galaxy.  They examined the trans-
    mission of the planetary radar of Arecibo and the ballistic missile 
    early warning systems (BMEWS).  For the calculation of maximum range 
    R, the standard range equation is: 

        R=(EIRP/(4PI PHImin))exp(1/2)

        Where PHImin is the sensitivity of the search system in [W m-2].
    For the NASA HRMS Target Search PHImin = 10exp (-27) and for the 
    NASA HRMS Sky Survey PHImin w 10exp(-23) (f)exp(1/2), where f is the
    frequency in GHz.  Table 3 shows the distances where the Arecibo and
    BMEWS transmissions could be detected by a similar NASA HRMS
    spectrometer. 

    TABLE 3: HRMS Sensitivity for Earth's Most Powerful Transmissions:

    ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

                          ARECIBO PLANETARY RADAR                     

    (1) TARGETED SEARCH                   MAXIMUM RANGE (light years)

          Unswitched               
            With CW detector               4217
            With pulse detector            2371
          Switched
            With CW detector               94
            With pulse detector            290

    (2) SKY SURVEY                  

          Unswitched
            CW detector                    77
          Switched
            CW detector                    9


                                  BMEWS

    (1) TARGETED SEARCH
          Pulse transmit CW detector       6
          Pulse transmit pulse detector    19

    (2) SKY SURVEY
          Pulse transmit CW detector       0.7

    ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

        All these calculations assumed that the transmitting civilization
    is at the same level of technological evolution as ours on Earth. 

        Von Hoerner (1961) classified the possible nature of the ETC
    signals into three general possibilities:  Local communication on
    the other planet, interstellar communication with certain distinct
    partners, and a desire to attract the attention of unknown future
    partners.  Thus he named them as local broadcast, long-distance calls,
    and contacting signals (beacons).  In most of the past fifty SETI
    radio projects, the strategy was with the hypothesis that there are
    several civilizations transmitting omnidirectional beacon signals. 
    Unfortunately, no one has been able to show any positive evidence 
    of this kind of beacon signal. 

        Another possibility is the radio detection of interstellar communi-
    cations between an ETC planet and possible space vehicles.  Vallee and 
    Simard-Normandin (1985) carried out a search for these kind of signals 
    near the galactic center.  Because one of the characteristics of arti-
    ficial transmitters (television, radar, etc.) is the highly polarized 
    signal (Sullivan et al, 1978), these researchers made seven observing 
    runs of roughly three days each in a program to scan for strongly 
    polarized radio signals at the wavelength of lambda=2.82 cm. 

        Radar Warning Signals

        Assuming that there is a certain number N of civilizations in 
    the galaxy at or beyond our own level of technical facility, and
    considering that each civilization is on or near a planet of a Main
    Sequence star where the planetoid and comet impact hazards are
    considered as serious as here, Lemarchand and Sagan (1993) considered
    the possibility for detecting some of these "intelligent activities"
    developed to warn of these potentially dangerous impacts. 

        Because line-of-sight radar astrometric measurements have much
    finer intrinsic fractional precision than their optical plane-of-sight
    counterparts, they are potentially valuable for refining the knowledge
    of planetoid and comet orbits.  Radar is an essential astrometric
    tool, yielding both a direct range to a nearby object and the radial
    velocity (with respect to the observer) from the Doppler shifted echo
    (Yeomans et al, 1987, Ostro et al, 1991, and Yeomans et al, 1992). 

        Since in our solar system, most of Earth's nearby planetoids are
    discovered as a result of their rapid motion across the sky, radar
    observations are therefore often immediately possible and appropriate.
    A single radar detection yields astronomy with a fractional precision
    that is several hundred times better than that of optical astrometry.
    The inclusion of radar with the optical data in the orbit solution 
    can quickly and dramatically reduce future ephemeris uncertainty.  It
    provides both impact parameter and impact ellipse estimates.  This
    kind of radar research gives a clearer picture of the object to be
    intercepted and the orientation of asymmetric bodies prior to
    interception.  This is particularly important for eccentric or
    multiple objects. 

        Radar is also the unique tool capable for making a survey of such
    small objects at all angles with respect to the central star.  It can
    also measure reflectivity and polarization to obtain physical
    characteristics and composition. 

        For this case, we can assume that each of the extraterrestrial
    civilizations in the galaxy maintains as good a radar planetoid and/or
    comet detection and analysis facility as is needed, either on the
    surface of their planet, in orbit, or on one of their possible moons. 

        The threshold for the Equivalent Isotropic Radiated Power (EIRP)
    of the radar signal could be roughly estimated by the size of the
    object (D) that they want to detect (according to the impact hazard)
    and the distance to the inhabited planet (R), in order to have enough
    time to avoid the collision. 

        One of the most important issues for the success of SETI
    observations on Earth is the ability of an observer to detect an ETC
    signal.  This factor is proportional to the received spectral flux
    density of the radiation.  That is, the power per unit area per unit
    frequency interval.  The flux density will be proportional to the EIRP
    divided by the spectral bandwidth of the transmitting radar signals B.

        The EIRP is defined as the product of the transmitted power and
    directive antenna gain in the direction of the receiver as EIRP =
    PT.G, where PT is the transmitting power and G the antenna gain.  
    This quantity has units of [W/Hz]. 

        According to the kind of object that the ETC wants to detect
    (nearby planetoids, comets, spacecraft, etc.), the distance from the
    radar system and the selected wavelength, a galactic civilization that
    wants to finish a full-sky survey in only one year, will arise from a
    modest "Type 0" (w10exp13 W/Hz, Rw0.4 A.U., Dw5000 m, and lambdaw1 m)
    to the transition from "Type I" to "Type II" (w2x10exp24 W/Hz, Rw0.4
    A.U., Dw10 m, lambdaw1 mm). 

        Lemarchand and Sagan (1993) also presented a detailed description
    of the expected signal characteristics, as well as the most favorable
    positions in the sky to find one of these signals.  They also have
    compared the capability of detection of these transmissions by each
    present and near future SETI projects. 

        Infrared Waves

        There have been some proposals to search in the infrared region
    for beacon signals beamed at us (Lawton, 1971, and Townes, 1983). 
    Basically, the higher gain available from antennas at shorter
    wavelengths (up to 10exp14 Hz) compensates for the higher quantum
    noise in the receiver and wider noise bandwidth at higher frequencies.
    One concludes that for the same transmitter powers and directed
    transmission which takes advantage of the high gain, the detectable
    signal-to-noise ratio is comparable at 10 micro-m and 21 cm.  Since
    non-thermal carbon dioxide (CO2) emissions have been detected in the
    atmospheres of both Venus and Mars (Demming and Mumma, 1983), Rather
    (1991) suggested the possibility that an advanced society could
    construct transmitters of enormous power by orbiting large mirrors to
    create a high-gain maser from the natural amplification provided by
    the inverted atmospheric lines. 

        An observation program around three hundred nearby solar-type
    stars has just begun (Tarter, 1992) by Albert Betz (University of
    Colorado) and Charles Townes (University of California at Berkeley).
    These observations are currently being made on one of the two 1.7-
    meter elements of an IR interferometer at Mount Wilson observatory. 
    On average, 21 hours of observing time per month is available for 
    searching for evidence of technological signals. 

        Dyson (1959, 1966) proposed the search for huge artificial
    biospheres created around a star by an intelligent species as part
    of its technological growth and expansion within a planetary system. 
    This giant structure would most likely be formed by a swarm of
    artificial habitats and mini-planets capable of intercepting
    essentially all the radiant energy from the parent star. 

        According to Dyson (1966), the mass of a planet like Jupiter could
    be used to construct an immense shell which could surround the central
    star, having a radius of one Astronomical Unit (A.U.).  The volume of
    such a sphere would be 4cr2S, where r is the radius of the sphere (1
    A.U.) and S the thickness.  He imagined a shell or layer of rigidly
    built objects Dw10exp6 kilometers in diameter arranged to move in
    orbits around the star.  The minimum number of objects required to
    form a complete spherical shell [2] is about N=4 PIrexp2/Dexp2w2x10exp5 
    objects. 

        This kind of object, known as a "Dyson Sphere", would be a very
    powerful source of infrared radiation.  Dyson predicted the peak of
    the radiation at ten micrometers. 

        The Dyson Sphere is certainly a grand, far-reaching concept. 
    There have been some investigations to find them in the IRAS database
    (V. I. Slysh, 1984; Jugaku and Nishimura, 1991; and Kardashev and
    Zhuravlev, 1992). 

    ==================================================================
    2 - The concept of this extraterrestrial construct was first 
    described in the science fiction novel STAR MAKER by Olaf 
    Stapledon in 1937.
    ==================================================================

        Optical Waves

        In the radio domain, there have been several proposals to use the
    visible region of the spectrum for interstellar communications.  Since
    the first proposal by Schwartz and Townes (1961), intensive research 
    has been performed on the possible use of lasers for interstellar 
    communication. 

        Ross (1979) examined the great advantages of using short pulses in
    the nanosecond regime at high energy per pulse at very low duty cycle.
    This proposal was  experimentally explored by Shvartsman (1987) and
    Beskin (1993), using a Multichannel Analyzer of Nanosecond Intensity
    Alterations (MANIA), from the six-meter telescope in Russia.  This
    equipment allows photon arrival times to be determined with an
    accuracy of 5x10exp(-8) seconds, the dead time being 3x10exp(-7)
    seconds and the maximum intensity of the incoming photon flux is
    2x10exp4 counts/seconds. 

        In 1993, MANIA was used from the 2.15-meter telescope of the
    Complejo Astronomico El Leoncito in Argentina, to examine fifty nearby
    solar-type stars for the presence of laser pulses (Lemarchand et al,
    1993). 

        Other interesting proposals and analysis of the advantages of
    lasers 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 , 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. 

        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 rela-
    tively 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 geolo-
    gical time periods, provided that the star has a sufficiently shallow 
    outer convective zone.  They have estimated that the abundance anoma-
    lies resulting from the slow neutron fission of plutonium-239 and
    uranium-233 could be duplicated (compared with the natural nucleosyn-
    thesis processes), if this process takes place. 

        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 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. 

        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 character-
    istic 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.  

        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.

        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

        The Author -

      ==================================================================
      |                 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

