snow lines

Noun

snow line (plural snow lines)

1. The altitude, in a mountainous region, above which the ground is covered with snow, at any particular time.

   Synonyms:

   snow level

2. The inner limit where volatile molecules can remain frozen in the zone around a star.
   • Chris Ormel, an astronomer at the University of Amsterdam, and his colleagues recently calculated that protoplanets began to form at the snow line around the star, then grew quickly by accreting pebbles.2018 April 26, Alexandra Witze, “Earth May Have Been Formed by a Bunch of Tiny Space Pebbles”, in The Atlantic

   Synonyms:

   frost line

3. (specifically) The limit for water remaining solid instead of evaporating away under solar radiation.