Re: Oxygen on exoplanets

>"Seán Hennessy" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> I've been reading lately about the proposed OWL telescope, which would
> have sufficient resolution to make direct observations of exoplanets. This
> would enable scientists to analyse their atmospheres spectroscopically and
> determine their composition.
>
> Now I understand that the presence of a gas like oxygen would be a strong
> indicator of the presence of life, since oxygen is very reactive and won't
> last in the atmosphere unless there is some process constantly
> replenishing it. Life is obviously such a process, but does anyone know if
> there are others, already known or speculative? Would the presence of
> oxygen be enough to allow us to safely infer the presence of life?

Well, oxygen and all the other elements of life too are detected within
stars,
but stars have no life (as we understand it anyway :-).

Oxygen detected on a planet would be very interesting though and
suggestive of life! However, oxygen (in my opinion) would not be the
definitive indicator of the presence of life. For example the planet may
have
water but no life (either never or "as yet"), but the ultraviolet light from
the
parent star could break down water into hydrogen and oxygen so one
would detect oxygen (but there would be no life present). After a time
the oxygen would disappear of course (as it has on Venus) ...

I think one would need to detect other molecules inorder to be absolutely
(or nearly so) certain that life as we know it was present on the planet.

Ozone for example would indicate that the oxygen was being not just
expended but formed by something on the planet to reach some
stable or steady-state condition (as on Earth).

Also, detection of methane in a more or less stable state (Carl Sagan
suggested this: "Pale Blue Dot" is one reference) in the presence of
oxygen would be another indicator of life present as we know it ...

Having these additional indicators would probably get scientists very
excited :-)

Al

>
> Thanks,
> Seán
>
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