Really Old Stars Perhaps Ideal for Advanced Civilizations
http://www.seti.org/site/apps/nl/content2.asp?c=ktJ2J9MMIsE&b=194993&ct=3760145

Really Old Stars Perhaps Ideal for Advanced Civilizations
by Edna DeVore, Director of Education and Public Outreach

Planets abound in the galaxy. Over the past decade, scientists have
discovered giant planets mostly by radial velocity techniques that
detect the spectral shift in a star's light caused by the to and fro tug
of an unseen planetary companion.
This method has detected more than 200 planets, dominantly large
close-in planets called "hot Jupiters" that are inhospitable to life as
we know it.
In the near future, with the launch of NASA's Kepler Mission in 2008,
we'll have the tools to seek evidence of Earth-size planets in the
habitable zone of distant stars.

The search for life beyond Earth is the search for a good place to live,
a habitable planet, in orbit about a long-lived star where life may
arise and evolve. The first place we looked was at stars like our own
Sun, a middle-sized, middle-aged star. G-Stars like the Sun are stable
for about 10 billion years, which is a good long time for planets to
form, and life to evolve. We also expected to find solar systems like
our own with small terrestrial planets near the star, and larger gaseous
planets farther out. This particular pre-conception was discarded with
the discovery of hot Jupiters on 4-day orbits about their stars.

The idea that other, less-massive, dimmer stars than the Sun could also
host habitable worlds has long been debated. A particular class,
M-Stars, are of interest simply because there are so many of them?they
are the most common star in the galaxy. They're the cool stars that
inhabit our neighborhood.
There's considerable interest in the question of whether M-Stars could
host habitable planets. Would the planets be tidally locked with one
face always directed toward the M-Star? Would flares wipe out life on
the local planet? If M-Stars could host habitable planets, life may be
much more widespread that we've previously thought. Thus, M-Stars are of
interest to astrobiologists including SETI scientists who are searching
for life beyond Earth.

In July 2005, a team of SETI institute scientists, as part of our NASA
Astrobiology Institute research program, brought together a diverse
group of scientists to consider?frankly reconsider?the possibility
of life on planets orbiting M-Stars. The results of this workshop are
now published as the current issue of "Astrobiology": Search for
Habitable Planets Outside Earth's Solar System.  According to the
publisher, "These reports present the preliminary results and
conclusions from recent studies on the habitability of M Star Planets,
which are planets about the size and mass of Earth that contain
sufficient amounts of carbon dioxide (CO2) in their atmosphere to
support a stable source of water on the planet's surface.

The habitability of terrestrial planets depends in large part on the
distance of their orbit from the nearest star. Most of the stars closest
to the Earth's Sun are characterized as M Stars, and planets orbiting M
Stars are of particular importance in the ongoing Darwin/Terrestrial
Planet Finder missions being developed jointly by the U.S. National
Aeronautics and Space Administration (NASA) and the European Space
Agency (ESA)."

The collected papers present the current understanding of M-stars,
explore various aspects of M Stars (including dwarf M Stars and low mass
M Stars), describe efforts to simulate Earth-like planets, consider the
possible greenhouse effects in the atmosphere of Earth-like planets, and
review the spectral signatures of photosynthesis.
"M stars are the most accessible, yet challenging, targets for habitable
zone terrestrial planet searches," says journal Editor-in-Chief, Sherry
L. Cady, Ph.D., Associate Professor in the Department of Geology at
Portland State University. "The potential for M Star habitable zone
planets to evolve biospheres and retain them are but two of the many
reasons to include M stars in the search for evidence of life beyond the
confines of Earth."

Why are SETI scientists interested in M-Stars? As Dr. Peter Backus,
Observing Programs Manager for SETI, concluded in a preliminary report
on the M-Stars workshop, "One?aspect of M dwarfs makes them intriguing
for SETI: they may be ideal hosts for advanced technological
civilizations because they live an extraordinarily long time. Stars like
the Sun live (i.e., they fuse hydrogen into helium) for only about 10
billion years. No M dwarf that ever formed has yet to die; no M dwarf
will die for more than another 100 billion years. With such long
lifetimes, there are big possibilities for these small stars."