Search for extraterrestrial life moves to forefront 
In S.F., space scientists agree on central theme for exploration 

David Perlman, Chronicle Science Editor   Monday, December 15, 2003 
  

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As NASA pursues unmanned missions throughout the solar system, the
quest for signs of life on distant planets -- more likely in the past
than in the present -- is gaining increased attention from space
agency planners.

The problems are formidable: They must increase their understanding of
how life originated and evolved on Earth; they must deduce the most
likely places where water could have existed on planets like Mars; and
they must develop new techniques for drilling many yards, and later
many miles, beneath the surface of such planets.

Finally, the scientists must be scrupulously careful with every
spacecraft and every tool that lands on any planet to make sure they
do not carry microbes from Earth that would contaminate whatever
extraterrestrial life might conceivably exist now or in the past.

At last week's annual meeting of the American Geophysical Union in San
Francisco, NASA-sponsored scientists from many research institutions
called their search for life on other planets and their moons "a
unifying theme'' for solar system exploration.

"Astrobiology is now the intellectual centerpiece of NASA's efforts in
space exploration," said Bruce M. Jakosky, professor of geology at the
University of Colorado, referring to the new field that integrates
astronomy with the study of life.

Mars and Europa, the ice-covered moon of Jupiter, "appear as
potentially habitable worlds, either today or in the past," he said.
"And the smoggy atmosphere of Saturn's moon Titan may well cover a
surface where intermittent water and organic chemicals might have
encouraged the evolution of living organisms."

As a result of recent discoveries of microbes living in freezing cold,
with no oxygen or light, and the profound pressures of deep
underground mines, Jakosky noted, the extreme diversity of life on
Earth makes it quite likely that life could be or have been widespread
in our solar system.

"We could probably pick up some bugs right now on Earth that would
find themselves quite happy in a Martian environment," he said.

For 30 years, scientists scanning images of Mars from spacecraft have
been tantalized by giant channels, broad basins and sinuous valleys on
the Martian surface that look exactly as if water had flooded and
flowed there billions of years ago.

In coming weeks, three spacecrafts -- one stationary lander operated
by the European Space Agency and two NASA rovers -- will set down on
the Red Planet and search for signs of past and present life, and
water.

In an even more ambitious mission, astronomers and astrobiologists
said at last week's AGU meeting that they have begun planning a voyage
to Europa to study what must be deep oceans -- and possibly life --
beneath the icy crust of the Jovian moon.

They envision sending a 300-foot-long, nuclear-powered craft -- called
JIMO, for Jupiter Icy Moons Orbiter -- to spend five years circling
Europa, plus two others, Callisto and Ganymede. Scientists have not
ruled out landing probes or instruments on the surface of Europa to
aid the search.

The mission will fly no earlier than 2010 and could cost as much as $8
billion.

As the space agency pursues missions to other planets, a major focus
is protecting those worlds and ourselves, said John D. Rummel, who
bears a unique title as NASA's "planetary protection officer'' in
Washington. "As we discover life out there, we don't want to find that
we've already killed it off."

International space treaties require space-faring nations to develop
foolproof techniques for rigorously sterilizing every object --
spacecraft or instrument -- that is designed to approach or land on a
planet, he said. Similarly, when spacecraft are planned to return to
Earth, they must be built so there is no possibility of unknowingly
bringing an alien organism back to Earth.

Back when the Apollo program was carrying astronauts to the moon,
their samples of lunar rock were quarantined for months, and their
instruments were sterilized. Because the job will be infinitely more
difficult for the robotic planetary explorers, teams of scientists are
already developing the crucial anti-contamination technology, Rummel
said.

NASA has created a major "Astrobiology Institute" with its
headquarters at the Ames Research Center in Mountain View, with some
20 universities and research institutions participating.

Geochemist David J. Des Marais, an astrobiology researcher at Ames,
noted the importance of understanding the evolution of life on Earth
if scientists are ever to understand how life might have developed on
planets elsewhere.

His own research into how life developed suggests that water must have
first rained down on the new-forming Earth from comets and meteors as
much as 4.9 billion years ago and that more massive impacts introduced
organic chemicals within an additional billion years.

"Proto-cells" then began to form on the warming Earth. And finally by
3.7 billion years ago, the first life appeared along the coasts of
small, new continents in the form of "biofilms" and layers of
microbial mats whose fossil forms have been discovered in recent
years.

Within a few hundred million years, those microbes had learned to use
sunlight for energy, growth and reproduction. After a few million
years, more advanced life forms emerged. And after that, the pace of
evolution and growth of diversity increased swiftly, he noted.

"Understanding the nature and timing of this ascent of life is crucial
for discerning our own beginnings," Des Marais said. "This
understanding also empowers our search for the origins, evolution and
distribution of life elsewhere in our solar system and beyond."