Space Forum / SETI / March 2007

It takes little difference in chemistry and histories and environments to produce different base chemistries which last quite a
while. Its
a little wierd to say it but its like baking a cake vs muffins vs bread
vs pastas! They all use flour. A pinch of this or that, presence of
soda or no soda, different cooking temps and viola! A different
planetary chemistry. Once the environment has cooled the chemistries set and become stable for the long term. Not unlike
how a few atoms made everything & diversity. Maybe not unlike
how the very Laws of Physics were set in stone for the long term
after initial competition and sorting out, as Oppenheimer thought.
The implication is, there were other options but a selection
process occurrs, and this determines the final outcomes....

As for Titan's methane, current thought says its of geological
origin vs organic. Critics of that theory say that only an organic
process could account for the methane replacement necessary to
keep Titan in a methane steady state very long, because methane
would dissapate quickly, on the geological clock. The issue
is unsresolved.

But the landing was very real! Awesome. A triumph.

Best to you -

KLM

RD> But what I am curious about is where this methane came
RD> from. Anyone ?  What are the anorganic processes that create
RD> methane (in the super cooled environment of Titan) ?

Methane is CH_4.  Hydrogen is the most abundant element, carbon is the
fourth-most abundant element (after helium and oxygen).  Thus, methane
is easy to create.

RD> And why is there so much on Titan, while other moons of Saturn
RD> have none of the stuff ??

How do you reach that conclusion?  Note that very often when people
describe a moon as "icy," they mean not only water ice but frozen
methane and ammonia as well.

RD> In general, I am amazed how different the composition is between
RD> the various planets in the solar system and even between moons
RD> around the gas giants.  Why does Titan have an atmosphere of
RD> nitrogen, while Ganymede have virtually no atmosphere at all.  Why
RD> does Venus have a very dense antmosphere of almost only CO2, Earth
RD> has almost all nitrogen, while Mars has no atmosphere to speak of.
RD> Does anyone have any plausible explanation for where all this
RD> diversity originates from ?

For the terrestrial planets, I believe that this is some hint of
understanding.  First, Mars is a lot smaller than either Earth or
Venus, which means it has less gravity and more difficulty holding
onto an atmosphere.  Also, it has no magnetic field, so its atmosphere
gets blasted by the solar wind.

In the case of Venus and Earth, my dim recollection is that they have
the same amount of carbon.  The difference is that Earth's oceans
allow the carbon to be absorbed and incorporated into rocks.  Because
Venus is closer to the Sun, its oceans evaporated long ago.  (There's
indirect evidence for Venus having had oceans by the
hydrogen/deuterium ratio in its atmosphere.)  In Venus' case, once in
the atmosphere, there's no way for the carbon to be recycled into
rocks.