A Johns Hopkins astronomer is a member of a team that
last week briefed fellow scientists
about plans to use new technology to take advantage of
recent, promising ideas on where to search for
possible extraterrestrial intelligence in our galaxy.
Richard Conn Henry, a professor in the Krieger
School's Henry A.
Rowland Department of
Physics and Astronomy, is joining forces with Seth
Shostak of the SETI Institute and Steven Kilston
of the Henry Foundation Inc., a Silver Spring, Md., think
tank, to search a swath of the sky known as
the ecliptic plane. The three propose to use the new Allen
Telescope Array, operated as a partnership
between the SETI Institute in Mountain View, Calif., and
the Radio Astronomy Laboratory at the
University of California, Berkeley.
Comprising hundreds of specially produced small dishes
that marry modern, miniaturized
electronics and innovative technologies with computer
processing, the ATA provides researchers with
the capability to search for possible signals from
technologically advanced civilizations elsewhere in
our galaxy — if, in fact, such civilizations exist
and are transmitting in this direction.
Employing this new equipment in a unique, targeted
search for possible civilizations enhances
the chances of finding one, in the same way that a search
for a needle in a haystack is made easier if
one knows at least approximately where the needle was
dropped, said Henry, who spoke about the
proposal at the American Astronomical Society annual
meeting in St. Louis.
According to the researchers, the critical place to
look is in the ecliptic, a great circle around
the sky that represents the plane of Earth's orbit and
comprises only about 3 percent of the sky. The
sun, as viewed from Earth, appears to pass annually along
this circle; any civilization that lies within a
fraction of a degree of the ecliptic could detect Earth
passing in front of the sun.
"If those civilizations are out there — and we
don't know that they are — those that inhabit star
systems that lie close to the plane of the Earth's orbit
around the sun will be the most motivated to
send communication signals toward Earth," Henry said,
"because those civilizations will surely have
detected our annual transit across the face of the sun,
telling them that Earth lies in a habitable
zone, where liquid water is stable. Through spectroscopic
analysis of our atmosphere, they will know
that Earth likely bears life.
"Knowing where to look tremendously reduces the amount
of radio telescope time we will need
to conduct the search," he said.
Most of the 100 billion stars in our Milky Way galaxy
are located in the galactic plane, forming
another great circle around the sky. The two great circles
intersect near Taurus and Sagittarius, two
constellations opposite each other in the Earth's sky
— areas where the search will initially
Kilston said, "The crucial implication is that this
targeted search in a favored part of the sky —
the ecliptic stripe, if you will — may provide us
with significantly better prospects for detecting
extraterrestrials than has any previous search effort."
Ray Villard of the Space Telescope Science Institute,
who will join the team in its observations,
said that in November 2001, STScI publicized Hubble Space
Telescope observations of a transiting
planet and "it occurred to me that alien civilizations
along the ecliptic would likely be doing similar
observations of Earth.
"Once they had determined Earth to be habitable, they
might initiate sending signals," Villard
Shostak of SETI notes that the Allen Telescope Array
is ideal for the team's plans to search
the entire ecliptic over time, and not just the
intersections of the ecliptic and galactic planes.
The team's presentation at the AAS meeting also
explored possible scenarios for the
appearance of civilizations in our galaxy.
"These models are nothing but pure speculation. But
hey É it is educational to explore
possibilities," Henry said. "We have no idea how many, if
any, other civilizations there are in our
galaxy. One critical factor is how long a civilization
— for example, our own — remains in existence.
we dearly hope, the answer is many millions of years, then
even if civilizations are fairly rare, those in
our ecliptic plane will have learned of our existence. They
will know that life exists on Earth, and they
will have the patience to beam easily detectable radio, or
optical, signals in our direction, if necessary,
for millions of years in the hope, now realized, that a
technological civilization will appear on Earth."