Sky & Telescope - May 2021 - 84

FOCAL POINT by Robert Gray

The " Wow " Now

After four decades, a mysterious radio signal from space remains excessively elusive.

at Ohio State University recorded the
so-called Wow signal (S&T: Oct. 2012,
p. 86). It was the best candidate for an
interstellar radio signal found during
the university's seven-year search for
extraterrestrial intelligence (ETI). It's
also one of the best ever reported and
the most well known.
In the more than four decades since,
I've searched for the Wow signal a
half-dozen times, because detecting it a
second time might mean the discovery
of ETI. I'm not a professional astronomer, but I know enough about radio
telescopes to use them in searches for
ETI, and I usually collaborate with a
trained astronomer.
Gerry Harp, some of his colleagues
at the SETI Institute, and I recently
had the longest listen ever for the
Wow signal - 100 hours using the
Allen Telescope Array in California.
We've reached a conclusion about that
enigmatic signal picked up so long ago.
Before sharing that, though, I'd like
to tell you about some of the possibilities that have been considered, to show
what a thorough job has been done.
Perhaps, I thought early on, the
signal just required patient observing
to detect again. The Ohio State radio
telescope could only " see " the spot on
the sky from which the signal may have
originated for a few minutes each day.
I built a 12-foot radio telescope and
looked at that spot for 15 minutes a
day for several years. But I didn't see a
repetition of the signal, possibly because
the antenna was too small.
Perhaps the Wow was an occasional
hailing signal intended to attract
attention to a similar but weaker
signal that's present all the time. With
Kevin Marvel (American Astronomical
Society), I looked for signals 100 times
weaker using the Very Large Array with
84

M AY 2 0 2 1 * S K Y & T E L E S C O P E

27 antennas each 82 feet in diameter.
But we found only feeble natural radio
sources in one hour of observing.
Perhaps it was a lighthouse-like signal that illuminates us for a few minutes every few hours. Simon Ellingsen
(University of Tasmania) and I observed
for 14-hour stretches using the Hobart
26-meter radio telescope in Tasmania.
But we found only the glow of hydrogen
and some obvious interference.
Perhaps it was a transmission from
the surface of a planet that pings us
" daily " as the planet rotates. The 100hour Allen search should have caught a
signal repeating as rarely as once every
terrestrial day or two. But we didn't ﬁnd
anything like the Ohio State signal in
the expected area of sky.
Failing to ﬁnd the Wow signal after
so many attempts, we conclude that
the signal was most likely humanmade,
maybe due to an aircraft or satellite,

although the 1420 MHz Wow frequency
is protected worldwide. That's disappointing, but following up on good
candidates is worthwhile. And it's just
possible that some sort of signal is present that these searches missed, such as
a very narrowband signal. Surprisingly,
nobody has ever looked for a narrowband signal with a modern SETI system.
Although the Wow signal hasn't
proved to be from ETI, there's still the
chance that, if ETI exists, we may be
able to detect its presence across the
void by looking for technosignatures
like radio signals and biosignatures in
atmospheric gases (see page 34). Finding
either one would be a historic discovery
and tell us something about our place
in the scheme of things.
ROBERT GRAY, a consultant based
in Chicago, authored The Elusive Wow:
Searching for Extraterrestrial Intelligence.

LE AH TISCIONE / S&T

IN 1977, THE BIG EAR radio telescope

Sky & Telescope - May 2021

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