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In
1894 Percival Lowell with his 450mm
refractor telescope near Flagstaff Arizona described a network of
canals which he believed he could see and which he felt was a clear
sign of intelligent life on the planet Mars. And with H. G. Wells The
War of the Worlds published shortly after it was easy for the
general population to believe that an intelligent and possibly even
hostile alien civilization existed on the relatively near by red
planet.
By
the mid twentieth century while there was still optimistic hope that
there may be some kind of life on Mars, as Mars is the most Earth
like planet in the Solar System it was clearly not a highly
developed life and not an extraterrestrial civilization!
If
there is no other intelligent life on Mars and by extension within
our Solar System perhaps with there being somewhere between 200
to 400 billion stars in our Milky Way galaxy alone and perhaps with
a large percentage of these stars having planetary systems and with
the possibility of even a very small percentage of these planets harbouring
life, it is easy to imagine the possibility of thousands
of highly developed civilizations out there.
It
was clear from the start that we or they would find it near to
technically impossible to physically travel the enormous distance
too or from even the nearest stars. With nearest star to earth being
the faint Proxima Centauri at a distance
of 4.3 light-years and a light-year translating into about
9,460,000,000,000 kilometres, we will without some fundamental break
through in technology never traverse these distances physically.
The
obvious choice was not to go there personally, but instead send or
listen for a message from the distant
civilizations. With
the refinements in radio technology in particular sensitive VHF and
microwave technology developed for radar during World War II we had
a method.
How many
civilizations could really be out there? (The
Drake equation)
Astronomer Frank Drake penned an equation in 1960 as part of his preparation
for what was known as the Green Bank meeting: that established SETI
(Search for Extraterrestrial Intelligence). The equation aimed to
get handle on the odd of there being extraterrestrial
civilizations within our galaxy and to create some order to the
issues that needed to be discussed at the conference. The equation
has since taken on a life of its own and is quoted in most books and
web sites on the subject and is the corner stone of much scientific
discussion within SETI.
The equation is as follows:
Where:
is
the number of civilizations in our galaxy that may be capable of
contact.
 is the average rate of star formation in our galaxy.
is the fraction of those stars that have planets
is the average
number
of planets that can potentially support life per star that has
planets
 is the fraction of the above that actually go on to develop
life at some point.
 is the fraction of the above that actually go on to develop
intelligent life.
 is the fraction of the above that develop a technological
civilization that emits detectable signs of their existence into
space. i.e.
radio
 is the length of time such a civilization emits detectable
signals into space.
There is obviously great debate over what values should be
place in the equation as perhaps only
and
can
be estimated on the bases of real scientific observational data.
The values used by Drake and fellow scientist in 1960 were:
= 10/year (ten new stars are formed on average per year over
the life of the galaxy)
=
0.5 (half of all stars will have planets)
= 2
(stars with planets will have 2 capable of supporting life)
=
1
(100% of these planets will develop life)
=
0.01 (1% of which will develop intelligent life)
=
0.01 (1% of which will emit detectable signals into space)
=
10,000 (This civilization will emit signals for 10,000years)
The
galaxy is still big place and most or all of the 10 may still be
well out of radio range. The bottom line is that most of the numbers
are little more than a guess and you can get all sorts of results
from less than 1 to thousands subject to what you think the values
could be. We are certain that the number should be at least one!
The
most recent guestimation
has produced a result of two. Them and us would you believe!
What
is the call frequency?
The
radio spectrum is enormous if you are aiming to detect a very weak
and very narrow band signal.
Nature has determined that a band of frequencies from just
above 1000MHz to about 10,000MHz is galatically quiet and that
atmospheric absorption is low, this is the terrestrial microwave
window. This is also still a large amount of spectrum that is also
increasing be used for all sorts of human communications from mobile
phones to wireless broadband etc.
A
frequency known as the hydrogen line at 1420.40575 MHz has been
chosen as it is a frequency or call channel that is universal and
would be known by any technically advanced civilization. It is for
this reason that the frequency range from 1400.00MHz to 1427.00MHz
have been assigned exclusively to radio astronomy and no other
activity is allowed.
In April 1960 astronomer Frank Drake performed one of the first modern
experiments named "Project Ozma" used a 25-meter-diameter
radio telescope at Green Bank,
West Virginia
, to examine a small number of stars near the 1.420 gigahertz marker
frequency. A 400 kilohertz band pass was scanned around the marker
frequency, using a single-channel receiver with a bandwidth of 100
hertz. The information was stored on tape for off-line analysis. He
found nothing of interest.
A few years later during 1967 a large radio telescope was conducting
experimental observation at 81MHz of the effects of the Sun's
solar wind on distant Quasar radio sources. An odd radio signal was
identified and when plotted on a chart recorder revealing a
continuous series of pulses spaced perfectly every 1.337 seconds.
The signal was confirmed as coming from deep space, but nothing like
this had been seen before. It had to be seriously considered as a
message or perhaps an extraterrestrial beacon. The signal was
labeled LGM1 which stood for "Little Green Men" first contact.
Evidence including the fact that there was no Doppler shift that would have
be expected if the signal was coming from a planet of satellite
orbiting a distant star. The source was in fact coming from a star
its self, a rapidly rotating neutron star. A neutron star is the
remnant core of supernova, an exploding giant star. As the star
explodes throwing of massive amounts of material the core is driven
inward along with the collapse of the remaining star material. A
super dense object only several tens of km in diameter remains. As a
result the object spins up and can be rotating as much 50 times a
second. The highly compressed magnetic fields produced by the
neutron star channels light and radio waves like a rotating search
light. These object tuned out not to be an extraterrestrial radio
beacon, but rather the discovery of one of natures strangest
objects, the Pulsar. Over a thousand Pulsars have now been
identified.
The 'WOW' signal
On 15 August
1977 Dr Jerry Ehman a project volunteer for the Ohio State
University SETI project witnessed a startlingly strong signal from
the radio telescope. He circled the characters on the printout and
scribbled "Wow" in the margin. This lone signal is considered by
some as the most likely detection of an extraterrestrial signal ever
received, but has not been detected again.
The circled
character code on the print 6EQUJ5 represents the amplitude
variation of the signal. A space denotes amplitudes of between 0 and
0.999; the number 1 denotes the amplitude between 1 and 1.999, 2
represents 2 - 2.999 and so on. 10 and above are represented by
letters, 10 - 10.999 is displayed as A, 11 - 11.999 is displayed
B etc. The value of 'U' representing an intensity of between
30.0 and 30.999 and was the highest value recorded. The intensity is
a representation of the signal to general background noise.
The columns in
the print out correspond
to 10kHz-wide channels starting with channel 1 to the left and
channel 2 with the signal of interest. The general frequency is
around 1420.405MHz known as the hydrogen line.
I have plotted
the values on the below graph to give a clearer view of the rise and
fall of the signal.
Ohio
State
University's radio telescope known as Big
Ear was a fixed antenna and used the Earths rotation to scan the
sky. The beam width of the antenna and the rotation of the Earth
meant that the Big Ear could observe a given point in the sky for
only 72 seconds. An extraterrestrial signal would therefore be
expected last for exactly 72 seconds and peak after 36 seconds as
the signal past over the antenna's window and would then decay
over the remaining 36 seconds.
While the WOW
signal may have been an Earth-bound signal that simply got reflected
off a piece of space junk the duration and shape of the signal and
the fact that it was narrow band corresponds to what would be
expected of a signal of extraterrestrial origin.
The case for the WOW signal being real!
The 1420.405MHz
channel falls within the 1400-1427MHz protected allocation for radio
astronomy and should therefore be free of transmissions.
Unless it was a
fairly high orbiting piece of space junk the WOW signal should have
had a different duration. Longer if the piece of space junk was
tracking with the rotation of the earth or shorter if it were
tracking in most other directions with relation to the rotation of
the earth.
I have not been
able to find any reports of checks for known space junk orbits,
however as NORAD (North
American Aerospace Defence Command) actively tracks tens of
thousands of these objects I would have assumed that this would have
been a relatively easy task.
It
all hangs on this; the signal duration implies that it came from
space well beyond earth. The signal was very narrow band implying
that it was artificial. That's it!
The case for doubt for the WOW signal!
The two issues that cast serious
doubt on the WOW signal are first that despite being relatively
strong it has never been heard of again.
Second and
perhaps more serious is this; the Ohio State radio telescope uses
two focal points, situated side by side. Any cosmic radio source
would be seen first by one for 72 seconds and then about three
minutes later by the other for a period of 72 seconds.
The WOW signal
produced a whopping 60 Jansky signal level on the first antenna, but
was not detected by the second. While it is possible that the signal
simply went off the air within the 3 minute period, this would have
to seem bloody unlucky to say the least, but it is possible.
Incredibly the
WOW signal is after nearly 50 years of listening, the most
tantalizingly possible signal heard thus far.
Making ourselves known.
Every hour of
every day for more than half a century human civilization has been
accidentally sending highly visible radio signals into space. From
the viewpoint of a distant extraterrestrial
observer the rotating Earth radiates bright pulses of
electromagnetic energy across the radio spectrum. The flashes of
radio emissions are a result of the rising and setting of hundreds
of powerful radio stations, television transmitters, microwave links
etc peppered around the globe. Although these transmitters generally
radiate parallel to the surface of the Earth as these signals pass
beyond the horizon they ultimately radiate out into the cosmos. In
fact so much radiation is now leaking of into space that the Earth
is near as an intense a radio source as the Sun.
Therefore if
anyone is listening for as far as 50 light-years from us, they
already know what we're up to.
The big
question is will our new space friends interpret Big
Brother as a sign of intelligent life?
A more
conscious effort was made in the 1970s with the launched four probes
by the United States
to survey the outer planets of the Solar System with a trajectory
that has destined them to leave the Solar System and sail out
amongst the stars for the rest of eternity. More
an act of faith and symbolism the spacecraft have plaques that if
found would communicate something about us to the finder. There was
at the time some controversy about the information contained in the
plaques as it depicted were we are, the fear was that if found
something, possibly hostile would be able to locate us.
The probes
Pioneer 10 and 11 probes launched in 1972 and 1973 carried a plaque
depicting the location of the Earth and solar system within the
galaxy and the form of the human body.
The Voyager 1
and 2 probes launched in 1977 carry two gold records that depict
again the human form, our solar system and its location and also
included are recordings of pictures and sounds from Earth.
Something to
ponder is this; long after the human race is gone and the Earth its
self is dead and lifeless these probes could be the longest lived
indication that we ever existed.
As every
amateur knows, if every one is just listing potentially good DX
contacts will go unrealized, therefore in 1974 the Arecibo radio
telescope, the largest radio telescopes in the world transmitted a
series of messages in the form of digital images.
The
Arecibo
message was a 1679 pixel image with 73 rows and 23 columns. It shows
the numbers one through ten, the atomic numbers of hydrogen, carbon,
nitrogen, oxygen, and phosphorus, a figure of a human being and its
height, the population of Earth, our solar system, and an image of
the
Arecibo
telescope with its diameter.
What is happening now?
At
present the SETI Institute a now privately funded organization has
been focusing on a joint project with
University
of
California Berkeley
to building a SETI-dedicated array of telescopes that will equal a
100-meter radio telescope, the Allen Telescope Array. It is the
forerunner of other larger radio astronomy arrays planned for later
in the decade. It is possible that as the telescope and SETI
technology advances we may be able to detect intelligence not by
directed message but by the same kind of 'noise' we accidentally
broadcast to the cosmos via radio, television and radar signals.
It is likely that SETI and the like is a waist of money and
effort as the current best technology at our disposal requires that
the signal be in cosmic terms very close, say 100 light-years at a
stretch. This is only covering about 0.1% of our Milky Way galaxy.
Remember the
Drake equation that estimates between two and ten possible
extraterrestrial civilizations within our entire galaxy. The odds
are really stacked against success.
However
the implications of an extraterrestrial contact on human culture and the way we see ourselve would
be profound. Imagine if we were able to establish ongo radio contact
with an extraterrestrial civilization 20 light-years away. Think
about it, it would change everything!
For more information on the WOW Signal see: http://www.bigear.org/Wow30th/wow30th.htm
For more information on the SETI Institute see: http://www.seti.org/
For more information on SETI Australia see: http://seti.uws.edu.au/
For more information on Pioneer 10
& 11: http://nssdc.gsfc.nasa.gov/planetary/pioneer10-11.html
For more information on Voyager 1
& 2: http://nssdc.gsfc.nasa.gov/planetary/voyager.html
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