Pale Blue Dot ( PDFDrive.com ) (1)

expect life on Mars, like life on Earth, to be organized around carbon-based molecules. To find no
such molecules at all was daunting for optimists among the exobiologists.
The apparently positive results of the life detection experiments is now generally attributed to
chemicals that oxidize the soil, deriving ultimately from ultraviolet sunlight (as discussed in the
previous chapter). There is still a handful of Viking scientists who wonder if there might be extremely
tough and competent organisms very thinly spread over the Martian soil—so their organic chemistry
could not be detected, but their metabolic processes could. Such scientists do not deny that
ultraviolet-generated oxidants are present in the Martian soil, but stress that no thorough explanation
of the liking life detection results from oxidants alone has been forthcoming. Tentative claims have
been made of organic matter in SNC meteorites, but they seem instead to be contaminants that have
entered the meteorite after its arrival on our world. So far, there are no claims of Martian microbes in
these rocks from the sky.
Perhaps because it seems to pander to public interest, NASA and most Viking scientists have been
very chary about pursuing the biological hypothesis. Even now, much more could be done in going
over the old data, in looking with Viking-type instruments at Antarctic and other soils that have few
microbes in them, in laboratory simulation of the role of oxidants in the Martian soil, and in designing
experiments to elucidate these matters—not excluding further searches for life—with future Mars
landers.
If indeed no unambiguous signatures of life were determined by a variety of sensitive experiments
at two sites 5,000 kilometers apart on a planet marked by global wind transport of fine particles, this
is at least suggestive that Mars may be, today at least, a lifeless planet. But if Mars is lifeless, we
have two planets, of virtually identical age and early conditions, evolving next door to one another in
the same polar system: Life evolves and proliferates on one, but not the other. Why?
Perhaps the chemical or fossil remains of early Martian life can still be found—subsurface, safely
protected from the ultraviolet radiation and its oxidation products that today fry the surface. Perhaps
in a rock face exposed by a landslide, or in the banks of an ancient river valley or dry lake bed, or in
the polar, laminated terrain, key evidence for life on another planet is waiting.
Despite its absence on the surface of Mars, the planet's two moons, Phobos and Deimos, seem to
be rich in complex organic matter dating back to the early history of the Solar System. The Soviet
Phobos 2 spacecraft found evidence of water vapor being out-gassed from Phobos, as if it has an icy
interior heated by radioactivity. The moons of Mars may have long ago been captured from
somewhere in the outer Solar System; conceivably, they are among the nearest available examples of
unaltered stuff from the earliest days of the Solar System. Phobos and Deimos are very small, each
roughly 10 kilometers across; the gravity they exert is nearly negligible. So it's comparatively easy to
rendezvous with them, land on them, examine them, use them as a base of operations to study Mars,
and then go home.
Mars calls, a storehouse of scientific information—important in its own right but also for the light
it casts on the environment of our own planet. There are mysteries waiting to be resolved about the
interior of Mars and its mode of origin, the nature of volcanos on a world without plate tectonics, the
sculpting of landforms on a planet with sandstorms undreamt of on Earth, glaciers and polar
landforms, the escape of planetary atmospheres, and the capture of moons—to mention a more or less