Digest Number 52

> Truly alien life would definitely have an alien signature, it wouldn't
> have DNA, RNA, and probably wouldn't metabolize the same sugars
> we do.
Since we have never found alien life, this does not follow. It could
be that whenever life evolves from various organic but still dead
molecules, several forms of self-replicating molecules are formed, but
Earth-style RNA and DNA wins because it is the most efficient.

> Then there is the Panspermia theory, namely that a piece of Mars
> was knocked off by an asteroid impact and contaminated Earth, or
> a piece of Earth got knocked off by an asteroid and contaminated
> Mars.
If we land unsterilized probes on Mars and later find microbial life
with Earth-style nucleic acids and the same correspondence between
triplets and aminos, we won't easily know if the explanation is
panspermia or recent contamination. Unless we find it so far down that
it certainly couldn't have migrated that far down since the unsterilized
probe landed.

> In either case the life found on Mars wouldn't be truly alien
> although its likely that it would have evolved since the
> contamination began, in that case you could tell the native
> Martian life from those microbes brought by astronauts by the
> fact that the native martian life would be better adapted to the
> Martian environment than would be the case from recent Earth
> imports.
This also does not follow. Micro-organisms evolve rapidly, when put
under evolutionary stress. Probably more slowly, if they can survive on
Mars, than they do on Earth, because the harsh Martian climate will
cause them to grow much more slowly and so have longer between
generations. Still, if we find them ten or fifty years after the
contamination, in some environment more clement than in most places -
suppose there is liquid ground water saturated with minerals somewhere
reachable through micro-cracks from the surface - many thousand
microbial generations may have passed, and they may have adapted enough
to make it difficult to compare them with known Terran species.

> << Rather, I imagine the Mars exploration to go somewhat like this:
> First, orbital industries are established, with whatever
> combination of lunar and asteroidal resources we find best.
> Space habitats of increasing size are built. A space habitat has
> an engine tacked onto it, and is sent to Mars orbit. From this
> permanent orbital base, Mars is observed remotely and with
> sterilized landers, until we know with reasonable certainty
> whether there is Martian life. >>

> You want to send a city ship over to explore Mars for the first time
> with space probes? In maybe 50 to 75 years after the Island Threes
> are built? You might as well talk about exploring Alpha Centauri by
> spaceship, I'll be just as dead then as I would when we finally
> explore Mars by city ship under your plan.
Who says 50 to 75 years after Island Three?? Once a number of Ones
have been built, a miniature Stanford Torus may be built and sent, or an
unshielded Island One, to be shielded by rocks from Phobos or Deimos.
It may happen earlier than that - it's quite conceivable that the first
space habitat is much smaller than Island One, perhaps some sort of
"Skerry One" big enough to build "Skerry Two", which then builds "Skerry
Three", and while or before Island One is built, a replica of Skerry
Three is built and sent to Mars. Whatever. I certainly don't imagine
that most of a human lifetime since the first Island Three pass before
we start exploring the solar system with movable cities. A single
Island Three is a *country*. When we're capable enough to build a One,
we're capable enough to build a small torus and send it to Martian
orbit.

> We can only confirm the existance of life if there is any, not its
> absence if there isn't.
True. But we can search the surface and determine with reasonable
certainty that there is no life. I did not propose investigating Mars
until we're as sure that it is barren as we're as sure of the
Pythagorean Theorem.

Jon L. Beck.