Here Be Dragons

HERE BE DRAGONS
ration of Mars will require the return of samples to Earth rather than
analysis on Mars, and NASA has made plans accordingly. There's a
mission planned for the year 2003 that will collect samples with a
rover. The rover will deliver the samples to a lander, which will fire
them into orbit. Another mission in 2006 will do the same thing
somewhere else on Mars. Then a French-built sample return vehicle,
launched in 2006, will rendezvous with one or both of the orbiting
caches and return them to Earth by 2008.
We ask McKay why we should be going to Mars for rocks when
Mars has already sent us a bunch. "All the Martian meteorites come
from volcanic terrains," he says. "That's maybe because only volcanic
rocks have enough integrity that when they're hit by a comet they stay
intact and launch off into space. A block of sandstone would just turn
to sand, and it will never make it. But volcanic rocks are not ideal for
searching for fossils. If you wanted to find fossils on Earth, landing on
Kilauea and taking samples would not be the ideal way. It would be
better to land on the Bonneville salt flats and take a sedimentary core."
On Earth, 3.5-billion-year-old fossils, such as Bill Schopf has found,
are extremely rare. But that's in large part because 3.5-billion-year-old
rocks are themselves rare, thanks to the constant recycling of the
Earth's lithosphere. In addition, when such rocks are found, they usually
turn out to have been altered by exposure to high temperature and
pressure within the Earth. "On Mars there's no tectonics or mountain
building or erosion," McKay reminds us. "We can see surfaces that are
3.8 billion years old—half the planet is that old. That doesn't mean
that it's going to be easy to find fossils, of course. It may be hard in a
different way."
If fossil microorganisms are found, that would still leave unresolved
the question of whether they belonged to an independent Life, or were
cousins to Schopf s terrestrial microbes. "We need the organic bodies,"
says McKay. To get them, he thinks, the most promising strategy
would be to drill about a kilometer into the ancient permafrost surrounding
the south polar cap. The idea would not be to get all the way
down to liquid water but to find ancient frozen sediments that could
harbor the remains of organisms dating from a more clement era.
"They'd be dead," he says, "but we'd be able to see if they used the
same twenty left-handed amino acids as we do, and DNA, and compare
it to Woese's tree of life." With the DNA, of course, one would be
halfway to a "Noachian Park." But given all the trouble that cloning dinosaurs
led to, NASA may think twice about cloning Martians.
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