Home' Technology Review : May June 2008 Contents ESSAY
TECHNOLOGY REVIEW MAY/JUNE
NASA, ESA, AND THE HUBBLE HERITAGE (STSCI/AURA)-ESA/HUBBLE COLLABORATION
People got very excited in 2004 when NASA's rover
Opportunity discovered evidence that Mars had
once been wet. Where there is water, there may be
life. After more than 40 years of human exploration,
culminating in the ongoing Mars Exploration Rover mis-
sion, scientists are planning still more missions to study the
planet. The Phoenix, an interagency scientific probe led by the
Lunar and Planetary Laboratory at the University of Arizona,
is scheduled to land in late May on Mars's frigid northern arc-
tic, where it will search for soils and ice that might be suitable
for microbial life (see "Mission to Mars," November/December
2007, and at TechnologyReview.com). The next decade might
see a Mars Sample Return mission, which would use robotic
systems to collect samples of Martian rocks, soils, and atmo-
sphere and return them to Earth. We could then analyze the
samples to see if they contain any traces of life, whether extinct
or still active.
Such a discovery would be of tremendous scientific signifi-
cance. What could be more fascinating than discovering life
that had evolved entirely independently of life here on Earth?
Many people would also find it heartening to learn that we are
not entirely alone in this vast, cold cosmos.
But I hope that our Mars probes discover nothing. It would
be good news if we find Mars to be sterile. Dead rocks and
lifeless sands would lift my spirit.
Conversely, if we discovered traces of some simple, extinct
life-form---some bacteria, some algae---it would be bad news.
If we found fossils of something more advanced, perhaps
something that looked like the remnants of a trilobite or even
the skeleton of a small mammal, it would be very bad news.
The more complex the life-form we found, the more depress-
ing the news would be. I would find it interesting, certainly---
but a bad omen for the future of the human race.
How do I arrive at this conclusion? I begin by reflecting
on a well-known fact. UFO spotters, Raëlian cultists, and
self-certified alien abductees notwithstanding, humans
have, to date, seen no sign of any extraterrestrial civiliza-
tion. We have not received any visitors from space, nor have
our radio telescopes detected any signals transmitted by any
extraterrestrial civilization. The Search for Extra-Terrestrial
Intelligence (SETI) has been going for nearly half a century,
employing increasingly powerful telescopes and data-mining
techniques; so far, it has consistently corroborated the null
hypothesis. As best we have been able to determine, the night
sky is empty and silent. The question "Where are they?" is
thus at least as pertinent today as it was when the physicist
Enrico Fermi first posed it during a lunch discussion with
some of his colleagues at the Los Alamos National Labora-
tory back in 1950.
Here is another fact: the observable universe contains on
the order of 100 billion galaxies, and there are on the order
of 100 billion stars in our galaxy alone. In the last couple of
decades, we have learned that many of these stars have planets
circling them; several hundred such "exoplanets" have been
discovered to date. Most of these are gigantic, since it is very
di cult to detect smaller exoplanets using current methods.
(In most cases, the planets cannot be directly observed. Their
existence is inferred from their gravitational influence on
their parent suns, which wobble slightly when pulled toward
large orbiting planets, or from slight fluctuations in luminos-
ity when the planets partially eclipse their suns.) We have
every reason to believe that the observable universe contains
vast numbers of solar systems, including many with planets
that are Earth-like, at least in the sense of having masses and
temperatures similar to those of our own orb. We also know
that many of these solar systems are older than ours.
From these two facts it follows that the evolutionary path
to life-forms capable of space colonization leads through a
"Great Filter," which can be thought of as a probability bar-
rier. (I borrow this term from Robin Hanson, an economist
at George Mason University.) The filter consists of one or
more evolutionary transitions or steps that must be traversed
WHY I HOPE THE SEARCH FOR EXTRA
TERRESTRIAL LIFE FINDS NOTHING.
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