Since yesterday's posting went down so well, I thought that I would go ahead
and post this one as well. Although I received this notice yesterday
afternoon, I didn't have time to copy it here then.

I thought that the experiment described below was an extremely clever one. At
the NASA Institute of Advanced Concepts meeting that I mentioned I attended
last week, the keynote speaker was Seth Shostak of the SETI Institute in the
Bay Area. Shostak gives about four public talks a month. He's an enormously
enjoyable speaker to listen to and if you get the chance, don't miss him.

But my opinions regarding the probablility of our detecting another
civilization in space haven't changed since we first discussed the
possibility here in regards to [log in to unmask] We really aren't talking about
discovering intelligent life in the various SETI projects; we're talking
about discovering civilizations who are at the same point in time in their
evolutionary development as we are: builders of radio. Abraham Lincoln and
Charlemagne were as intelligent as anyone alive today, but neither of them
could build radio transmitters or even gave much thought to the process.

The question of greatest interest is then: in the 10-15 billion year
histories of the most Sun-like, stable stars, what percentage of time will
radio-transmitting civilizations exist? In our case, the answer (so far) is
100/4,650,000,000 or 1 chance in 46500000.

When Shostak asked how many people in the audience believed that we would
discover intelligent life in the universe, everyone in the audience save one
enthusiastically raised their hands. Then he asked how many people didn't
think we would. I was the only one. All probability is against the
likelihood.

On the other hand, life should be nearly ubiquitous. It began here on earth
virtually as soon as it possibly could, within the first half billion years
of the planet's existence. What the experiment mentioned below has done is
verify that life's signature -- as evidenced by the atmospheric presence of
oxygen, water and methane -- is detectable in the faint reflectance of
earthshine off of the darkened portion of the new moon. Carl Sagan used to
like to talk about the fact that life's surest signature is a non-equilibrium
atmospheric chemistry. The presence of atmospheric oxygen is among the surest
signs of than non-equilibrium chemistry, especially at earth temperatures.
Without the presence of life on the surface of the earth to constantly
replenish that oxygen, all oxygen in the atmosphere would almost immediately
disappear.

The basic experiment described below is going to be one of the keys to the
Terrestrial Planet Finder spacecraft that will be launched sometime in the
next 20 to 40 years. At that time, we really are going to find out how common
life is -- rather than continue to merely believe that it should be as common
as warm mud.

Wirt Atmar

=======================================
<A HREF="http://cfa-www.harvard.edu/press/pr0223.html">
http://cfa-www.harvard.edu/press/pr0223.html</A>


 Harvard-Smithsonian Center for Astrophysics
 Release No.: 02-23
 For Release: October 30, 2002

                       ASTRONOMERS FIND LIFE ON EARTH

 Cambridge, MA - Now that the discovery of extrasolar planets, or planets
 around distant stars, has become relatively routine, scientists are now
 tackling the next step: finding life-bearing worlds. To do this, observers
 must know what signs to look for in the feeble light from these faraway
 planets.

 Astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA), in
 collaboration with researchers at the University of Arizona's Steward
 Observatory, have identified key signatures of life by studying
 Earthshine-the light of the Earth reflected off the dark side of the Moon.
 They found clear signs of water and an oxygen atmosphere, as well as
 tentative signs of plant life. Their findings give a clear indication of
 what "fingerprints" to search for when seeking life on Earth-like worlds
 orbiting distant stars.

 "Our research is paving the way for future missions like the Terrestrial
 Planet Finder," says Smithsonian astronomer Wes Traub. "Hopefully, within
 the next 10 years astronomers will be able to confidently say that some
 as-yet-undiscovered planet is a living world like our own."

 Archetypal Earth

 So far, astronomers can only detect Jupiter-like planets around other
 stars because such planets are large and create strong gravitational
 signals. However, as technology continues to improve, astronomers soon
 will be able to locate Earth-like extrasolar planets and study their dim
 light to search for signs of life. To know what to look for, they must use
 the example of the one planet where life is known to exist: the Earth.

 To replicate the view that a distant astronomer would have if studying the
 Earth from another planet, Traub and his colleagues used the nearby Moon
 as a mirror. Using the Steward Observatory 90-inch telescope at Kitt Peak,
 Arizona, they measured both the light of Earthshine from the Moon and the
 light of the Moon itself, then corrected the Earthshine to determine how
 the Earth would appear to a faraway observer. They compared this measured
 spectrum to a model created by Traub and CfA's Ken Jucks.

 The team found that Earthlight shows strong evidence for water - a
 necessary ingredient for life as we know it - and for molecular oxygen,
 which must be continually replenished by the processes of life to remain
 in the atmosphere. They also found features that suggested the presence of
 chlorophyll, indicating the existence of land plants.

 The latter showed up as bright reflections in the far-red region of the
 visible spectrum. This "red edge" is a well-known signature of
 chlorophyll, which appears green to us only because our eyes aren't very
 sensitive at the red end of the visible spectrum.

 The team also suggests that changes for finding life-bearing worlds are
 improved because the signatures can develop early in a planet's history
 and last for a long time. Our home planet has maintained an oxygen
 atmosphere for the past two billion years, and has shown a "red edge"
 since the first land plants evolved 500 million years ago.

 "If someone out there is watching our solar system," Traub points out,
 "they could have detected plant life here long before any intelligent life
 appeared."

 Findings Match Galileo

 These measurements complement those made by the Galileo spacecraft during
 a 1990 fly-by of Earth. As reported in the October 21, 1993 issue of
 Nature, instruments aboard the spacecraft also found evidence of gaseous
 oxygen and land plants.

 However, the Galileo measurements were made while it was close to the
 Earth and show conditions only in limited areas of the planet's surface.
 Studying Earthlight, on the other hand, yields a spectrum integrated over
 the entire visible surface of the planet, which matches the view that
 would be available to a distant astronomer in another star system.

 The measurements by Traub and his colleagues, reported in the July 20,
 2002 issue of The Astrophysical Journal, were taken over two nights. The
 astronomers suggest that follow-up studies be conducted over a longer
 period of time to see how Earthlight changes as different areas of the
 planet rotate into view, and as cloud cover changes.

 NOTE TO EDITORS: An artist's depiction of our world when the Earthshine
 measurements were taken, enhanced to show the "red edge" from vegetation,
 is online at <A
HREF="http://cfa-www.harvard.edu/ep/pressrel/pr0223_image.html">
http://cfa-www.harvard.edu/ep/pressrel/pr0223_image.html</A>

 Headquartered in Cambridge, Massachusetts, the Harvard-Smithsonian Center
 for Astrophysics (CfA) is a joint collaboration between the Smithsonian
 Astrophysical Observatory and the Harvard College Observatory. CfA
 scientists organized into seven research divisions study the origin,
 evolution, and ultimate fate of the universe.

 For more information, contact: David A. Aguilar
 Director of Public Affairs
 Harvard-Smithsonian Center for Astrophysics
 617-495-7462
 [log in to unmask]

 Christine Lafon
 Public Affairs Specialist
 Harvard-Smithsonian Center for Astrophysics
 Phone: 617-495-7463, Fax: 617-495-7016
 [log in to unmask]

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