Sky & Telescope - November 2024 - 84

GRAPH-PAPER DRAWING: COURTESY OF THE AUTHORS; ILLUSTRATION: BEATRIZ INGLESSIS / S&T
FOCAL POINT by Rich Isaacman and Linda French
At left is the Cornell
team's solution to Carl
Sagan's challenge,
drawn on graph paper
during the all-nighter
described below.
Message in a Molecule
Career scientists revisit a Carl Sagan challenge they undertook nearly half a century ago.
IN 1974, Arecibo Observatory was
about to begin a second life. The
world's largest radio telescope had just
undergone a major upgrade, sporting a
new, smoother surface and a powerful
1-megawatt radar transmitter.
That November - 50 years ago this
month - the observatory staff celebrated
the telescope's upgrade with the
symbolic transmission of what became
known as the " Arecibo Message, " a
23-by-73-bit raster image illustrating
some key facts about our species. Its
creators were Carl Sagan, observatory
director Frank Drake, staff scientist
James C. G. Walker, and one of us
(Rich, then a Cornell graduate student).
But Sagan's interest in alien intelligence
didn't end with transmitting
such a message. What would happen, he
wondered, if humanity were to receive
one? Would we be able to decode and
interpret it?
About a year later, Sagan got the
chance to perform the experiment
- albeit only with humans - while
producing a BBC TV documentary
about life on other worlds. Working
with a (to us) anonymous collaborator,
Sagan developed a binary message.
He then proposed to the BBC that he
would challenge a group of Cornell grad
students to interpret it. The director
84 NOVEMBER 2024 * SKY & TELESCOPE
and film crew would interview them
afterwards about their outcome.
Thus, late on a Friday in March 1976,
Sagan summoned six of us and presented
his challenge. The tight shooting
schedule required us to complete it
within 36 hours. Besides the two of us,
there were Richard French, Kathy Rages,
Edward Dunham, and David Pieri (all
of whom, like the two of us, went on to
successful careers in astronomy).
But what a challenge it was: a daunting,
19-page printout of ones and zeros
- 29,791 of them, as Sagan informed
us. With our calculators, we quickly
determined that to be the cube of 31.
During the all-nighter that followed,
we debated whether we were grappling
with a time sequence of 31 frames (each
31-by-31 pixels) or a 3D object. We
set to work with graph paper, coloring
squares for hours, then arranging them
to see if they suggested a sequence.
But each frame looked like a bunch of
circles; it made for a perplexing movie.
A 3D object, then. Kathy, endowed
with impressive visualization skills,
drew a perspective view of the stacked
images. The circles soon revealed
themselves to be cross sections of four
connected spheres floating in a cubical
frame: one large, with two small ones
on top and a medium-size one underneath.
It looked disturbingly like an
interstellar Mickey Mouse.
Maybe a molecule? Bingo. Linda said,
" It looks like formaldehyde, H2CO. " A
midnight run to the chemistry library
confirmed that suspicion, right down to
the bond angles.
But why waste so much data to
depict one simple molecule? Rich, the
radio astronomer, knew that H2CO
emitted a spectral line at a frequency
of 4.83 GHz, and the message became
clear: The " aliens " - Sagan's partner
turned out to be Nobel-laureate chemist
Linus Pauling - were telling us that
they could send vastly more information,
and that we should tune our
receivers to 4.83 GHz to get the goods.
We delivered our report in the
morning. Sagan was delighted, and the
film crew suitably awed. They called us
" bloody geniuses " ; he, in a public lecture
later that year, deemed us " reasonably
clever. " We like to think that was an
attempt at dry humor, and we're still
quite proud of the adventure.
¢ RICH ISAACMAN is a retired NASA
program manager. LINDA FRENCH is
Professor Emerita of Physics at Illinois
Wesleyan University. See Sagan and
the six-student team in this 1976 video:
https://is.gd/SaganChallenge.

https://www.is.gd/SaganChallenge

Sky & Telescope - November 2024

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