The term itself is borrowed from the notion of "frost line" in soil science, which describes the maximum depth from the surface that groundwater can freeze.
Occasionally, the term snow line is also used to represent the present distance at which water ice can be stable (even under direct sunlight).
[6] For example, the dwarf planet Ceres with semi-major axis of 2.77 AU lies almost exactly on the lower estimation for water snow line during the formation of the Solar System.
[13][14] Earth, which lies less than a quarter of the distance to the frost line but is not a giant planet, has adequate gravitation for keeping methane, ammonia, and water vapor from escaping it.
[15] The underlying mechanism may be the thermal instability of snow line on the timescales of 1,000 - 10,000 years, resulting in periodic deposition of dust material in relatively narrow circumstellar rings.