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I have an ammonia world, I.e., ammonia is a solvent. It is tidally locked to its Sun. To counter low temperatures, I can either have a hot core or high atmospheric pressure. The size of plant is earth like. The Sun is either a large K type or a smaller G type.

What is the limits on how high can I go with the atmospheric temperature?

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  • $\begingroup$ Why are you worried about cold temperatures? Can't you make the atmospheric pressure what you like and just have your planet closer to its star, or a hotter star? $\endgroup$
    – Willk
    Jul 6 '21 at 15:43
  • $\begingroup$ @willk , aren't ammonia planets generally very cold unless you introduce too many more variants? Maybe my research is wrong and has led me to believe that it is default for ammonia planets to be very cold and increasing atmospheric pressure is one way to counter it. I have kept the planet closer to my star but all articles still point to colder climes $\endgroup$
    – mukul215
    Jul 6 '21 at 16:22
  • $\begingroup$ The gas escape velocity diagram is posted somewhere on the WB stack once a week. Here is one. worldbuilding.stackexchange.com/questions/189995/… Escape velocity for NH3 is the same for water. If you can have water you can have ammonia. Very cold temperatures would help a little planet to hang on to its atmosphere but if you have an earth size planet you can have ammonia with earth type temperatures. $\endgroup$
    – Willk
    Jul 6 '21 at 21:02
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Just look at the phase diagram of ammonia, there you will get the values of (P,T) where ammonia is liquid.

enter image description here

In particular it seems that at around 113 bar you can have liquid ammonia between -77 C and 132 C.

Above 113 bar you would have a supercritical fluid, with no distinction between liquid and gaseous phase.

A supercritical fluid (SCF) is any substance at a temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid

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  • $\begingroup$ thanks. But is 100 atm survivable by complex life? That is another thing that would limit the atm values I can have. $\endgroup$
    – mukul215
    Jul 6 '21 at 12:42
  • $\begingroup$ @mukul215 100 atm is what you get under 1 km of water. Fishes live well below that. $\endgroup$
    – L.Dutch
    Jul 6 '21 at 12:44
  • $\begingroup$ One last thing, if you please can. Higher atm has a denser atmosphere and possibly higher gravity and higher temperature of the planet as well. At 100 atm, won't the planet temperature shift to higher en of the temperature range that you mentioned? $\endgroup$
    – mukul215
    Jul 6 '21 at 12:51

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