
Originally Posted by
Ophiolite
In a thread on water vapour talk turned to presence of water in space. Obviously remarked "Weird that the discussion in this topic changed like this But I'm glad it did. This is quite interesting."
Since it might be interesting to others I thought I would throw out some thoughts.
This is a brief summary I gave in that thread:
As we all doubtless know, hydrogen is the most abundant element in the universe. Oxygen is the third most abundant element. Where temperature is sufficiently low to allow molecular species to survive, water moelcules will form. Water vapour has been detected and found to be common around newly forming stars.
In the accretion discs of such stars, more distant from the proto-star, temperatures are suffciently low that ices will form. These progressively grow through collision and gravitational attraction, forming planetesimals composed of ices and mineral grains and organic molecules. Some of these contribute to the formation of gas and ice giants, such as Jupiter and Neptune, others will provide the oceans of Earth analogues. while many millions will be cast into the outer darkness of the system as comets.
Which bore a pleasing symmetry with this abstract:
Delsemme, A.H. Have comets played a role in the primary organic syntheses? Advances in Space research 1989
Primary organic syntheses first occurred in interstellar space, where more than sixty different organic molecules have been identified. The most important identifications for prebiotic chemistry probably are HCN, H2CO, CH3CN, C2H2 and CH3C2H, although many others could play important roles. A fraction of these molecules condense, with ubiquitous H2O and CO2, on interstellar grains that follow suit when a molecular cloud collapses gravitationally to form a star. An accretion disk surrounds the growing star, and the frosty interstellar grains are more or less heated depending on their distance to the central star. The innermost loose their water and carbon compounds and will form the rocky planets; those at intermediate distances loose most of their water only, and will form the parent bodies of the carbonaceous chondrites. The outermost keep all their frost and will become the comets. Eventually, the orbits of all those minor bodies diffuse into the inner solar system and bombard the inner rocky planets. Their numerous impacts has brought a veneer that explains the atmosphere and the oceans of the Earth, as well as the source of a wealth of organic compounds. Comets and carbonaceous chondrites are the messengers that have brought down to Earth the products of the primary organic syntheses that were ubiquitous in space.
The bottom line is that there is a wealth of prebiotic molecules in interstellar space, plus water. There are vast volumes of these in the interstellar clouds, where there is both more time and many orders of magnitude more material, and thus more opportunity, for primitive life to arise and subsequently seed young planets such as the Earth.
The more research that is carried out in this direction, the more likely I find that the origin of life is out there, not down here.