Thanks Suzy, its a pain when you find out there is much complexity in the answer for a question that seems relatively simple!
I guess when you look at something like methane it has to form ices under its freezing point which is...???, it starts to sublime at ???? temperature.
The temperature @ about 5 AU is...?????
Its a bit like blankety blanks!
So my question basic but as you have pointed out its not quite that simple! I was aiming to try and get information on Heliocentric distance / over temperature (K). Most comets do not start to produce a coma until its around 5 AU.....so whats the temperature (K) at which a coma starts to form??
Comets also get energy from the crystallisation of amorphous water ice, it is one mechanism to explain where a comets heat source might start at large heliocentric distances.
Hope that may help to explain what i'm trying to achieve.
Cheers!
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