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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 1603 times)
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #15
on:
February 04, 2010, 01:21:12 pm »
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:
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #16
on:
February 04, 2010, 01:21:26 pm »
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
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #17
on:
February 04, 2010, 01:21:40 pm »
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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
communications between an ETC planet and possible space vehicles.
Vallee and Simard-Normandin (1985) carried out a search for these
Page 7
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Jennifer Murdoch
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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #18
on:
February 04, 2010, 01:21:57 pm »
kind of signals near the galactic center. Because one of the
characteristics of artificial 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.
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Jennifer Murdoch
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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #19
on:
February 04, 2010, 01:22:14 pm »
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.
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Jennifer Murdoch
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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #20
on:
February 04, 2010, 01:22:24 pm »
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.
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Jennifer Murdoch
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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #21
on:
February 04, 2010, 01:22:37 pm »
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)
Page 8
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Jennifer Murdoch
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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #22
on:
February 04, 2010, 01:22:50 pm »
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).
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #23
on:
February 04, 2010, 01:23:04 pm »
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).
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Jennifer Murdoch
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Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #24
on:
February 04, 2010, 01:23:14 pm »
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.
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #25
on:
February 04, 2010, 01:23:25 pm »
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.
Page 9
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #26
on:
February 04, 2010, 01:23:38 pm »
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.
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #27
on:
February 04, 2010, 01:23:50 pm »
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.
==================================================================
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #28
on:
February 04, 2010, 01:24:03 pm »
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.
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Jennifer Murdoch
Superhero Member
Posts: 5235
Re: Detectability of Extraterrestrial Technological Activities
«
Reply #29
on:
February 04, 2010, 01:24:13 pm »
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
Page 10
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