Frost line

In astronomy or planetary science, the frost line, also known as the snow line or ice line is distance in the solar nebula from the central protostar where it is cool enough for hydrogen compounds such as water, ammonia, and methane to condense into solid ice grains.

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Post formation of of the Star System, and during the Stable Main Sequence of the a Viable Habitat System term used to for the present distance at which water ice can be stable (even under direct sunlight).

_This snow line distance is different from the formation frost line distance during the formation of a Star System. _

The reason for the difference is that during the formation of a System, the protostar nebula is an opaque cloud where temperatures were lower close to the protostar,[citation needed] and the star itself was less energetic.

If ice within Snow line is exposed to direct Starlight, then it sublimates on short timescales. However, out of direct sunlight ice can remain stable where temperature may be very low over the age of a Star System.

Frost line

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