Henry and colleagues think that we limit our search for
extra-terrestrial intelligence to the ecliptic plane in which
our solar system's planets orbit. This ecliptic band comprises only
about 3 percent of the sky, which could make it easier for scientists
to effectively narrow their search for intelligent ET.
The logic behind it postulates that if there is another, perhaps more
advanced alien civilization in our galaxy out there; they may be trying
to contact us, as well. If this is the case, Henry says a search
focused on the ecliptic "should lead rapidly to the detection of other
Exoplanets in the ecliptic should be able to see Earth passing in front
of the Sun. These transits are what Earth astronomers rely on to
identify a variety of information about the transiting planets, such as
radius, density and composition. Transits also reveal the secret’s of a
planet's atmosphere, therefore any potential alien astronomers studying
the Earth's spectrum would theoretically find the indicators of life in
our atmospheric oxygen, letting them know—just as we long to know—that
they are not alone.
Henry, along with his colleagues, plan to search the ecliptic for these
advanced alien civilizations with the Allen Telescope Array, a set of
dozens of antennae in Hat Creek, California, US.
According to Greg Laughlin, an astronomer and extrasolar planet hunter
at the University of California, Santa Cruz, if there is a stargazing
civilization trying to make contact with us within 50 light years, its
inhabitants would see the Earth as a bluish dot. All they would need is
an 8-metre space-based telescope with a good coronagraph along with a
set of space-based infrared telescopes, which would enable them to
detect ozone and water vapor in our atmosphere.
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 concentrate.
"We have no idea how many – if any – other civilizations there are in
our galaxy,” Henry noted. “One critical factor is how long a
civilization – for example, our own – remains in existence. If, as 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."
Posted by Rebecca Sato
Source: Johns Hopkins University