archive: SETI An Astrophysical Journal article

SETI An Astrophysical Journal article

Alfred A. Aburto Jr. ( (no email) )
Fri, 18 Dec 1998 07:49:17 -0800

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Hi, sorry about the text attachment (I keep forgetting
how to do the cut and paste procedures...). Interesting
article though ...

Al Aburto

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Date: Thu, 10 Dec 1998 09:26:47 -0500
From: Cheryl Gundy <>
Organization: Space Telescope Science Institute, Baltimore, MD 21218
Newsgroups: local.opo,local.tute,local.classifieds,sci.astro,

EMBARGOED UNTIL: 9 a.m. (EST) December 10, 1998

CONTACT: Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone: 410-338-4514)

Mario Livio
Space Telescope Science Institute, Baltimore, MD
(Phone: 410-338-4439)



If civilizations exist around other stars they are likely to be just
emerging across our Galaxy right now: like an apple orchard suddenly
maturing and ripening in the autumn sun.

So concludes Space Telescope Science Institute theorist Mario Livio,
in a paper to be published in the Astrophysical Journal.

Livio emphasizes that his theoretical work doesn't necessarily mean
extraterrestrial civilizations really do exist, but it shows they
cannot be dismissed either.

We would be a lonely, isolated quirk of cosmic evolution if
intelligent life forms appear on a planet at some random time in the
parent star's life, say some theorists.

Instead, Livio makes the case for a possible causal link between the
sun's lifetime and the appearance of intelligent life on earth. This
link should hold true for sun-like stars elsewhere in the universe:
offering an equal opportunity for intelligent life to arise elsewhere
in space.

The second part of his case is based on the possibility that carbon --
the fundamental building block of life as we know it -- may not have
been widely available until the universe was about 1/2 its present age.

This means that, given the added billions of years more required for
biological evolution, intelligent carbon-based life didn't make an
appearance any earlier than roughly 3 billion years ago.

He points out that before the universe could make life like us, it has
to make carbon atoms. The carbon was created by nuclear fusion in the
hearts of early stars, and then ejected when the stars lost their outer
gas layers and left their cores behind as white dwarfs.

Livio calculates that carbon production may have peaked only two
billion years before the sun and earth formed, based on estimates of
the star formation rate made with Hubble Telescope and other
ground-based telescopes.

Though life first emerged on earth a few hundred million years after
its formation, it took a vastly longer time - nearly 3 billion years --
for the first multi-celled organisms to appear. It took almost another
billion years before life emerged from the sea onto the land.

The earliest humans appeared less than 4 million years ago - at about
the halfway point in our sun's lifetime. If this were purely
coincidental, other theoreticians have argued, then it would take much
longer than the life of a star for most civilizations to arise. And so
it would be unlikely extraterrestrial civilization would come about at
all. We would be alone in the universe: reduced to a novelty - or
accident - of the cosmos.

Because sunlight provides far more energy for life than other chemical
processes, biological evolution is intimately linked to the sun's
behavior, Livio maintains. For example, the complex evolution of our
atmosphere is interrelated with the sun. Our planet's atmosphere had
to develop ozone to block out destructive UV radiation from the sun
before animals could emerge on the land

Likewise, he says, other civilizations should have emerged not much
sooner or later than about halfway through their parent star's life
cycle. That is, around stars like our sun, or slightly cooler, that
live healthy long stable lives and release enough energy to nurture
life on accompanying planets.

If Livio is correct, and the Galaxy may be blooming with new
civilizations, then where are they? Why haven't they visited us?

Livio cautions that his work does not prove the existence of
extraterrestrial civilizations, but points out that earlier
conclusions that they do not exist may be premature.

He says that that it's also risky to think civilizations would
colonize the Galaxy. "This assumes we have even the vaguest
understanding of the psychology of extraterrestrial civilizations."

He adds: "It's impossible to imagine the thinking of a civilization
which might have evolved a million of years ahead of humans. We
could be about as uninteresting to them as an amoeba is to us.
Actual proof will have to await advances in biology and astronomy."


The Space Telescope Science Institute is operated by the Association
of Universities for Research in Astronomy, Inc. (AURA) for NASA,
under contract with NASA's Goddard Space Flight Center, Greenbelt,
MD. The Hubble Space Telescope is a project of international
cooperation between NASA and the European Space Agency (ESA).

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