If an organic molecule can only survive a few hundred years (I guess it should be much shorter in time) in space, then it is a much much shorter time period than which is needed to form a denser clouds. How much time is needed for a diluted mass of gases to condense into a denser gas mass in space so that gas molecules at the center of the mass could be protected from the destruction of cosmic rays? Is hundreds of years long enough for that? I don't think so.
The sentence I quoted from
The Physics of the Interstellar Medium was '
Ultraviolet photodissociation occurs for most molecules
unshielded by grains in a few hundred years.' (Notice the emphases.) Molecules shielded by grains in dense opaque interstellar clouds survive much longer than molecules in the diffuse interstellar medium.
By the way, you can buy
The Physics of the Interstellar Medium from Amazon for $31.95; I think that you would learn from it. (No, I am not one of the authors.)
I do not know how long a dense cloud of gas takes to form out of the diffuse interstellar medium. The time for a dense cloud (
n ~ 10^11/m³) to collapse to a protostar in hydrostatic equilibrium is about 100,000 years.
However, your question is not strictly relevant. As I tried to explain previously, complex organic molecules are synthesized by ion-molecule reactions
inside dense opaque clouds
after the clouds have been formed. The ion-molecule reactions are initiated by the ionisation of H2 molecules by cosmic rays. According to Dyson and Williams (p. 41), in dense clouds (
n > 10^10/m³) 'the level of ionisation is probably controlled by [cosmic ray ionisation] (rather than by photons which will not penetrate such a dense cloud)'. Molecules formed by these ion-molecule reactions in opaque clouds, where they can be adsorbed onto dust grains, can survive for much longer than hundreds of years.
I am not talking about clouds that eventually formed the star. I am talking about the cloud which formed asteroids, comets and planets. I assume the cloud would more sparse and would take even longer time to condense into a comet (I even doubt if the function of condensation could do it at all).
Again, you have misunderstood the formation of stars and planets. Planets, asteroids and comets cannot form from
interstellar clouds; they form from the denser nebulae (protoplanetary discs, or 'proplyds') surrounding young stars. Terrestrial planets, asteroids and comets form by the accretion of solid particles, not by the gravitational instability of a cloud of gas. The evidence from meteorites shows that asteroids took a few million years to form, whereas the Earth took tens of millions of years. However, none of this is relevant to the formation and survival of molecules in dense interstellar clouds.
And the effect of "protection" could be simply negligible. To see the whole process in a simple picture, the destruction of any organic molecule in space should be much faster than its formation.
How do you make this out? Why do you think that the effect of protection would be negligible? After all, radio astronomers can observe the spectra of interstellar molecules (some of them quite complex organic compounds) in dense clouds, and can even measure their abundances; the dense clouds contain masses of organic compounds similar to the masses of the Earth or the Moon. As I have explained already, the clouds are opaque, so that rates of ultraviolet photo-dissociation are low, and the molecules are built up
inside the dense clouds by ion-molecule reactions initiated by cosmic ray ionisation of hydrogen molecules. Comets are formed from the dense protoplanetary disc surrounding the young star
after the collapse of the interstellar cloud.
If so, how is it possible to find any organic molecule embedded in a comet if the origin of organic molecule started from atoms?
It would be much more reasonable to assume the organic molecules found in comets are "residues" of a much much larger organic material.
This would only be reasonable if you could point to a 'much much larger organic material' that could be the source of the organic molecules in interstellar clouds and in comets. Can you do this?
It survived the cosmic destruction and deterioration and ended up as much smaller particles in the comet.
I have not heard of this. Can you explain what 'cosmic destruction and deterioration' you are talking about, and where you obtained your information about it? It would help if you could give a link to your source, or could cite a book or an article in a scientific journal.
