Download 15 Aug 2009

MODERN TIMES
Art Hobson
[email protected]
NWA Times 15 August 2009
On the trail of life in the universe
For at least 2000 years, humankind has speculated on the question "Are we
alone?" In the first century BCE, the Roman poet and philosopher Lucretius
suggested that, just as life originated by blind, spontaneous chemical interactions
on Earth, "we must acknowledge that such combinations of other atoms happen
elsewhere in the universe to make worlds such as this one …with races of different
men and different animals."
I expect we will discover extraterrestrial life within 15 years, although it's
highly unlikely to involve intelligent life and will probably be single-celled
microbial life, like simple algae or bacteria. It will be a landmark in human
history.
You live in the heroic age of exoplanet (planets around stars other than the
sun) discovery. Since all other stars can be seen only as a single point of
light, even the discovery of a single such planet is an awsome feat. The first
exoplanet was discovered in 1995, and 340 are now known. Encouragingly for
those of us who would be thrilled to find that the universe is filled with life, most
of the discovered planets lie in their star's "habitable zone" within which the star's
radiation has an intensity similar to the intensity of sunlight on Earth. So these
planets are candidates for having water in the liquid state rather than as steam or
ice. Life on Earth came from the oceans and is still made mostly of
water. Laboratory experiments suggest that, given an Earth-sized rocky planet plus
water, life is highly likely to develop through natural chemical processes. This is
probably how life developed on Earth.
To date, astronomers have discovered most exoplanets by detecting a star's
subtle wobbling in response to an orbiting planet. A star that wobbles sends out
light whose spectrum (or colors) wobble first toward violet and then toward red,
for the same reason (known as the Doppler effect) that an ambulance's siren
wobbles toward higher and then toward lower pitches as it approaches and then
recedes from you. Most such discoveries have been of large, Jupiter-like planets,
because high-mass planets cause big wobbles of the central star and so are easiest
to detect. These large planets are not so likely to harbor life. But the discoveries
indicate that the actual number of (mostly still undetected) planets rises steeply
with decreasing planet mass, making Earth-like planets highly likely. Most known
exoplanets orbit sun-like stars and smaller, cooler stars known as "red
dwarfs." Red dwarfs seem more likely than sun-like stars to be hosts for life, since
they comprise 80 percent of the stars near Earth and they give off their dim red
light steadily for far longer than our sun's 10-billion year lifetime (of which 5
billion years have now passed). Massachusetts Institute of Technology astronomer
Sara Seeger thinks that "infrared astronomy," based on invisible light whose
wavelength is a little longer than visible light's wavelength, might find signs of life
around a red dwarf within a few years.
A second method for detecting exoplanets concentrates only on those planets
that happen to orbit their star in such a way as to cross directly in front of the star
as seen from Earth. These "transiting" planets, while they are in front of their star,
reveal their presence by temporarily reducing slightly the light arriving at Earth
from the star. Careful monitoring of the reduced starlight, combined with
information from the star's Doppler effect, tells astronomers both the radius and
mass of the exoplanet and can reveal small rocky planets similar to ours. Sixty
transiting planets are known to date. A space-based transit survey by the European
Space Agency's Corot satellite has detected planets as small as two Earth
diameters. NASA's Kepler mission, launched this past March and named for the
great German astronomer who deciphered our solar (sun) system's architecture,
will monitor 100,000 sun-like stars. About 1 percent of these stars are expected to
have transiting Earth-like planets in their star's habitable zone.
A third method is the most technically difficult but offers the greatest
prospect for revealing life. It is the direct detection of an exoplanet's light--directly
seeing the planet. It's not easy to detect a planet's dim light in the many billion
times more intense glare of light from the planet's nearby star. To combat this
glare, astronomers must place a screen either inside or outside their telescope to
block the star's light while allowing the planet's light to enter the telescope. This
method will be perfected before long and can, by studying the precise frequencies
(or colors) of light from the planet, reveal the chemical signs of life.
The prospects are anybody's guess, but most of us who love to ponder this
question think that astronomers will find evidence that single-celled microbial life
exists around millions to billions of stars in our Milky Way galaxy alone. Because
our galaxy is only a tiny part of the universe, this would mean that the number of
instances of life in the universe is unimaginably large. But the prospects for
complex multi-cellular life are far more dim.
And the prospects for intelligent life are dimmer still. Here's one of the
reasons why: Judging from Earth's history, intelligent life requires billions of years
of evolution. Animal instincts develop during this period, and these primitive
instincts can be destructive in intelligent lifeforms unless they are rationally
controlled. Judging from humankind's destruction of our own environment, our
superstitious belief systems, and our uncontrolled violence, the prospects for such
rational control here and on other planets are not promising. Thus there might be
few if any surviving intelligent civilizations out there.