234
touched down on planets, such as
NASA’s Viking landers on Mars,
carried experiments to test for
signs of life. To date, no indication
of life, either past or present,
has been found, although some
unexplored corners of the solar
system remain candidates for life,
such as the deep oceans thought
to lie beneath the frozen surface
of Jupiter’s moon Europa.
Continued silence
No reply has ever been received
to any of the 10 interstellar radio
messages sent since 1962 and no
communication has been detected.
However, there have been false
alarms. The most famous of these
came in 1977, when an inexplicably
powerful blast of radio signals was
recorded coming from the direction
of the Chi Sagittarii star system
by Jerry Ehman at Ohio State
University. He circled the signals
on the readout and wrote “Wow!”
next to them. The “Wow!” signal
was never found again, however,
and recent research suggests that
it may have come from a hydrogen
cloud surrounding a comet.
Given the vast distances
between stars, it is still early days,
however. The Arecibo message will
not reach its target stars for another
25,000 years. Neither the Pioneer
plaques nor the gold-plated disks
carried by Voyagers 1 and 2—
the Voyager Golden Record—are
headed toward any particularLIFE ON OTHER PLANETS
star system. Unless they are
intercepted, they are destined to
wander the Milky Way eternally.
Sagan, for his part, believed that
to find life or to fail was a win-win
scenario—either result would show
something important about the
nature of the universe.SETI in the modern age
NASA struggled to maintain its
SETI funding, and today SETI is
privately funded. Since the 1980s,
the mantle has been taken up
by the SETI Institute, based in
Mountain View, California. UCal,
Berkeley, through its SETI@home
initiative, harnesses a network
of volunteer computers to trawl
Arecibo Observatory data for
patterns that might indicate an
unnatural radio source. Meanwhile,
in 2016, China announced the
completion of the largest ever radio
telescope, the Five-hundred-meter
Aperture Spherical Telescope
(FAST). Among other things, FAST
will search for extraterrestrial
communications. It will eventually
be made available to researchers
from around the world.The SETI Institute’s Allen
Telescope Array in California is
used daily to search for possible
alien communications, as well
as for radio astronomy.
Carl Sagan stands next to a model
of the Viking 1 lander. The lander sent
back signals from the surface of Mars
from 1976 to 1982. Its instruments
found no sign of life.