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In 1971, Sagan approached NASA
with the idea of sending a message
on its Pioneer spacecraft. Sagan
and Drake worked on a design
that would advertise Earth’s
existence to alien civilizations
and help them locate Earth in
the cosmos. The graphics on the
Pioneer plaque establish a unit
of measurement using the 21-cm
hydrogen emission line. Units
defined by reference to Earth-based
phenomena, such as meters and
seconds, would be meaningless
to extraterrestrial scientists. By
choosing units from properties
of nature, the hope was that they
would be understood universally.
All the images on the plaque
were scaled in terms of these units.
A map of bright and distinctive
pulsars points the direction to
Earth, and Pioneer’s route is traced
on a simple pictogram of the solar
system. Images of a man and a
woman were drawn by Sagan’s
artist wife, Linda Salzmann Sagan.
Pioneer 10 and Pioneer 11,
launched in 1972 and 1973, were
fitted with Sagan’s plaque, etched
on a 6- by 9-in (152 x 199 mm) gold-
anodized aluminum plate. Critics
warned that it would attract the
unwanted attentions of power-
hungry (or just hungry) aliens.
Feminist groups were unhappy
that the man waved in greeting,
while the woman’s pose angled her
body (they thought) submissively
toward the male figure. Salzmann
responded that women are smaller,
on average; that having both figures
waving might be interpreted as it
being the natural arm position; and
that she merely wished to show how
the hips moved. Sagan had initially
wanted the man and woman to be
holding hands, but decided it might
make the Earthlings look like a
single creature with two heads.The Arecibo message
While the search continued for
beacons set up by intelligent
beings and likely star systems,
Drake and Sagan decided to send
planet Earth’s own “we are here”
signal. The 3-minute burst of
1,000 kW radio waves was designed
to cross distances separating stars.
Beamed out from the Arecibo radio
dish in Puerto Rico in November
1974, the interstellar message was
aimed at the globular cluster M13,
a group of about 300,000 stars
25,000 light-years from Earth.
Instead of pictograms, the
Arecibo message took the form
of densely packed mathematical
code, consisting of 1,679 binary
digits (chosen because 1,679 is
a product of two prime numbers,
73 and 23). The digital message
contained the numbers 1 to 10
and information about the identity
of the sender—details about DNA,
the overall shape and dimensions
of a human, and the position of
planet Earth.NEW WINDOWS ON THE UNIVERSE
The Arecibo message was broadcast
into space a single time in 1974. Coded
in binary, its message is arranged in
73 rows of 23 columns.One of the hopes that accompanied
the robotic explorers, as they were
dispatched across the solar system
from the 1960s onward, was
that they might uncover some
indication of extraterrestrial life
within the solar system itself,
even if it were only single-celled
organisms. The spacecraft that ❯❯We began as wanderers, and
we are wanderers still. We
have lingered long enough
on the shores of the cosmic
ocean. We are ready at last
to set sail for the stars.
Carl Sagan