Science Questions

Where do comets get their water from?

Sun, 15th Nov 2009

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Nasa asked:

Where do comets get their water from?


We posed this question to Dr Mark McCaughrean...

Yes, I think one of the things you have realize is that when the solar system was very young, it was very much hotter.  And so, you had a lot of water in the solar system, but out at about Jupiter was pretty much evaporated off or incorporated into places like the Earth.  But the comets are very big lumps of icy dust and muck still leftover from the early part of the formation of the solar system.  Itís just leftover stuff.


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Nassar asked the Naked Scientists: I know that the water on Earth came from comets colliding into the Earth in its early history. But, where did the comets get the water from. Thanks... love the show. Nassar What do you think? Nassar, Sat, 6th Jun 2009

All the elements higher than lithium were formed and distributed through galaxies by supernova explosions initially they were just atomic nuclei but as they cooled the gradually gathered electrons (the electrons were always around because it stars are a neutral plasma)and became neutral atoms.  As the cooling process progressed  these atoms could form chemical compounds and as there was always lots of hydrogen around water and other hydrides are the more common compounds to be found as the gas cools down a lot these molecules tend to stick together to form interstellar granules which eventually get big enough to be comets. Soul Surfer, Sat, 6th Jun 2009

I suppose the polar nature of water, which allows it to make hydrogen bonds, also favours the aggregation of water molecules to form larger accumulations?

Chris chris, Sat, 13th Jun 2009

Very probably the presence of water on the surface of small particle will probably help them to stick together when the gravitiational attraction is too low to hold them together. Soul Surfer, Sun, 14th Jun 2009

Thanks Chris and Soul Surfer; these responses make sense. I was not too pleased with the response from the Astronomer in the podcast though. lunar11, Sun, 10th Jan 2010

I, too, had this question on the origin of water in comets and this thread has been useful. Thanks.

And I agree with @lunar11. The podcast (at about 49:30) did not answer the question: "It's just left-over stuff"!!! :/ sciencebloke, Sun, 11th Sep 2011

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