Re: Where did all the solar system's water come from?

We are born of the stars. Every atom in our bodies, and in all the things 
that surround us on Earth, was forged inside a star. Most people who think 
about such things are aware of the process of transformation of hydrogen 
into helium within stars. Our sun is not large enough to be able to do more 
than that, but heavier stars are able, as they age and grow hotter, to 
produce elements up to those as heavy as iron. Carbon, nitrogen, and oxygen 
are all very light elements, and are readily produced in stars not 
significantly more massive than the sun, When these heavier stars reach the 
end of their lives and become supernovae, they release all their elements 
into space in vast clouds of gas and dust. It was from such a cloud that we 
believe our solar system was formed. Significant amounts of hydrogen, and 
plenty of oxygen, nitrogen, and carbon were components of that cloud. We see 
the evidence of such lighter elements in the atmospheres of Venus, 
 http://www.windows.ucar.edu/cgi-bin/tour_def/venus/atmosphere.html

in the form of sulfur dioxide and carbon dioxide; Earth, in the form of 
nitrogen and hydrogen oxide (sometimes called "water"); Mars, in the form of 
carbon dioxide, and in the gas giants as free hydrogen, methane (CH4), 
ammonia (NH3), and other light-element compounds. Why is Earth the only 
"watery" planet? Two reasons: Mercury is too small and too close to the sun 
to hold any kind of atmosphere, Venus is too hot to sustain liquid water, 
and Mars, like Mercury, is too small to hold an atmosphere sufficient to 
maintain a water surface. Earth is conveniently sized and located to do both 
(though we are all aware these days that we are finely balanced on the tip 
of both a runaway ice age and a runaway greenhouse effect). The giant 
planets hold large quantities of water, though not, at their cloudtops, in 
liquid form. Certainly, many of their satellites consist mainly or entirely 
of water, Europa being a prime example. Water is a common compound in the 
universe; it would be much more surprising =not= to find it in our solar 
system. 

For more on the creation of elements in stellar environments, check out
 http://www.geocities.com:0080/CapeCanaveral/8851/fusion.html