(June 25, 2014 at 12:59 pm)JuliaL Wrote: "Comets are some of the material left over from the formation of the planets. "
"So the Sun is the collapsed core of an interstellar gas cloud, and the planets, asteroids and comets are small lumps of dust or ice chunks which stayed in orbit instead of spiraling into the Sun. "
So I gather that they formed something like giant snowflakes from the atomic hydrogen and oxygen which formed water in a dust and gas cloud.
Yap.
The reason why comets have much higher percentage of water than earth, even though both earth and comets formed out of what was originally the same material is simply this. Because earth started to form much closer to the infant sun, it comsisted of a high percentage of material from the part of the protoplanetary disk that had been close to the infant sun and had been baked dry by the radiant energy of the infant sun. As earth grew to large size, its gravity increased and ensured most of the material it collected from the solar nebula fell with great force. This further boiled off much of the water that did make it to the earth. So in the end earth was left mostly with rocks, which can withstand heat and solar radiation, and comparatively small inventory of water and gases.
Comets mostly formed far from the infant sun, where the radiant energy of the sun is slight, and not enough bake the raw material dry. Comets are small, and have little gravity, so most of the stuff a comet sweeps up from the protoplanetary nebula accreted to the comet with little force. So the water is not boiled off in the process of colliding with the comet. This is why comets are left with high percentage of water.
