SETI
The general usage of radio telescopes to monitor possible signals from extraterrestrial intelligence
has come to be known as the Search for Extraterrestrial Intelligence or SETI. There have
been some small government funded projects, but unfortunately SETI is an easy target for political demagogues
who decry the "frivolous" use of the taxpayer's money to search for intelligence among the
stars.
(In reality, the cost of a year of significant SETI research is less than that of a single advanced military
aircraft.)
Project Phoenix
Funding for the NASA SETI project was killed in 1993, but it continues as a privately funded endeavor called
Project Phoenix.
The movie Contact, based on the book by astronomer Carl Sagan,
was patterned loosely after portions of Project Phoenix. Here is a
discussion of the relation between real SETI and the one depicted in Contact
(see also the right panel).
An Extraterrestrial Signal
Project Phoenix has actually detected signals from
intelligent beings that come from
beyond the Solar System!
However, in this case, we are
the intelligent beings. The Pioneer 10 spacecraft, which
was launched by NASA in 1972,
is presently
about twice the
distance to Pluto and is thus very far
outside the planetary part of the Solar System
(headed in the general direction of the star Aldebaran, the Eye of the Bull,
with arrival scheduled in about 2 million years!).
The transmitter on Pioneer 10
was still functional until early 2003,
broadcasting a very weak signal of only a
few watts power. Therefore, it is a good example
of what a weak radio signal from a distant civilization might look like.
The top right figure shows a test of the Phoenix detection system.
The faint line across the
middle represents the frequency drift of the Pioneer 10 radio signal over time.
The Project Phoenix detection system does not
compensate for the motion of Earth during
observations. This means that ground-based radio
signals will have a constant frequency, but
signals from deep space will exhibit a drift in
frequency because of the changing relative
velocity between the source of the signal and the
Phoenix detectors fixed to Earth.