|MadSci Network: Astronomy|
Not very. First, the freezing point of N2O is *negative* 90.9 C, not positive 90.9 C. This is roughly equivalent to the temperature at which Jupiter formed (it's environment has cooled a little since it formed). The main problem with building a planet entirely of laughing gas is the presence of hydrogen & helium gas. Hydrogen & helium gas made up 98% of the nebula (space cloud of gas & dust) from which the solar system formed. Hydrogen and helium gas are very light, and where the terrestrial planets formed, it was too hot for them to condense onto the forming inner planets. However, in the outer solar system, it was cooler, so the hydrogen & helium gas could be captured by the forming outer planets. Jupiter and Saturn each captured so much of it that they are 90+% hydrogen & helium! In an environment where laughing gas could condense, the temperature is low enough that hydrogen & helium can be captured, and since they make up the vast majority of the solar nebula, outer planets will end up with large amounts of them. Also, given the abundance of hydrogen, oxygen, nitrogen, & carbon will form lots of "ices" with hydrogen - water ice, ammonia ice, methane ice. These "ices" are present in great amounts the outer planets too.
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