The Allen Telescope Array operated by the SETI institute.
The "Wow!" Signal
picked up by a SETI experiment at Ohio State University in 1977 often gets
mentioned, as it was the first time an ambiguous and still unexplained signal was picked up by at SETI experiment.
The signal was not witnessed in real time but rather was picked up over night while the experiment was running. Radio Astronomer Jerry R. Ehman saw
the signal on a computer printout the next morning and circled it with the word "Wow!" next to it:
The area which the "Wow!" signal of 1977 came from was not centered on any particular star.
It also never repeated. That area of sky has been searched several times since then and nothing was ever found.
(SIDENOTE: There was even a 72 second reply mimicking the original signal sent to the area of sky "Wow!" originated. This
was done in 2012
by the mostly useless "Chasing UFOs
program on NatGeo.)
That was then..... Fast forward to present day...
(click to enlarge)
In 2010 SETI picked up a new "Wow!" type signal, unlike the 1977 signal this one was not from that fairly blank area of sky.
This time the signal seemed to be from the vicinity of a star called TYC 1220-91-1 (An yellow G2V star around 100 light years away, almost identical
to our Sun but older) on the frequency of the number Pi multiplied by the Hydrogen line frequency (4462.3 *1420 Mhz) = ~4462.3 Mhz
And unlike the 1977 signal this one was detected and tracked in realtime. It only lasted 10 seconds but exhibited the characteristics an interstellar
beacon signal might be expected to, with the exception that it did not repeat. (I have my theory on why that is and how it may be recovered which I'll
get into later.)
That incident is mentioned on page 12 of the following paper on a new theoretical type of alien beacon:
"A new class of SETI beacons that contain information"
- G. R. Harp, R. F. Ackermann, Samantha K. Blair,
J. Arbunich, P. R. Backus, J. C. Tarter, - (Aug 22, 2010)
Here is an excerpt:
Figure 4 for example shows a result obtained in a narrowband SETI search near
the PiHI frequency (the number π times the HI observing line of 1420.4 MHz). This (extremely
powerful) ~10 second pulse of narrowband radiation appeared in one 50 second observation
period but was never re-observed. This pulse has interesting features: It is observed at a magic
frequency in the direction of a nearby and potentially habitable star. Yet we cannot be sure this
signal was created intentionally or unintentionally by some transmitter on Earth. Hence after
multiple observations over 2 weeks and no re-detection, we gave up (although this direction is
added to a catalogue of directions to re-observe as time permits).
Figure 4: A pulse with maximum power >300σ above the noise background was observed on a nearby
star (~100 LY, (J2000 RA, Dec) = (32.211809⁰, 22.441734⁰)) in the HabCat Catalog (Turnbull, 2003).
This pulse is interesting since it appears to arrive from the direction of a potentially habitable star and
because it appears very close (within the expected Doppler shift tolerance caused by relative motion)
to the “magic” PiHI frequency of 4462.3 MHz, this signal appeared in only one observation and never
thereafter. Given the proximity of this source, we do not expect substantial fading in the ISM; hence the
signal is really not present, most of the time.
(click to enlarge)...
So what happened essentially is SETI tuned to a "magic frequency" which an intelligent species might presumably place a beacon, and detected a loud
10 second signal which did not repeat, presumably from 100 light years away. The signal exhibited the Doppler shift that would be expected from an
interstellar signal rather than terrestrial interference and the signal source was close enough that SETI did not expect substantial fading due to
passage through the InterStellar Medium (ISM) which are clouds of gas and dust which can fade a continuous signal in and out. So SETI does not think
the signal is continuous or present most of the time.
My theory is that if this signal was in fact from a transmitter 100 light years away, that transmitter was not being used as a beacon for us but
rather was being used in a similar way as we use the Arecibo planetary radar, which by the way, can also be detected 100 light years away.
We use Arecibo and other such radars take pictures of near Earth asteroids.
When we do this we are not intending to signal anyone and the transmissions are typically a one time affair as different asteroids have different
trajectories so we aren't repeating these transmissions to the same areas of sky.
SETI essentially could have picked up a blip of another planet's asteroid avoidance radar. If that were the case, SETI would likely never see it
However it's also possible that such a transmission was some other type of radar which only sweeps that area of sky on an infrequent basis. An example
of this would be our radar studies of Venus or Mars.
Powerful facilities in the US (Arecibo, Goldstone Deep Space Communications Complex) and the Ukraine (RT-70 and Pluton) have been used to study
Mercury, Venus and Mars, including in some cases mapping their surfaces.
If the signal detected was from a planetary radar being used to study another body in the same vicinity as the transmitter such as a planet with a
regular orbit, then there is a long shot possibility that 24 hr a day/365 days a year monitoring of that section of sky on 4462 Mhz and other nearby
frequencies could produce a repeated observation at some point.
Arecibo at 100 light years away could be detected by a similar set up as the Allen Telescope Array.
The Square Kilometer Array
that is being built in the next decade or so will be able to detect the signal from an airport
radar tens of light years away and something like planetary radar perhaps hundreds of light years away:
So seeing a repeat is not out of the question if it really was some form of radar.
Unfortunately, it is impractical for professional SETI astronomers to simply sit on that frequency, stay fixated on TYC 1220-91-1 and look for that
signal to repeat. After all, there are plenty of other places and frequencies that need to be covered.
However, a sufficiently equipped amateur radio astronomer with a big enough dish could perhaps do nothing but look for a repeat of that signal from
the vicinity of that star and if the stars aligned (to use a pun) perhaps make the discovery of the ages.
One thing to note from the above information is that SETI did two things upon detecting such a signal:
1 - They published a paper which included all the relevant information on it.
2 - They never claimed the signal to be definitive evidence of aliens, though it looked from their perspective to be a signal of extraterrestrial
Instead they took a cautious approach, as they should. They didn't scream "aliens".
edit on 2-3-2014 by JadeStar because: (no reason