<Li> 3.1 AU (Martin and Livio, 2012) </Li> <Li> ≈ 150 K for μm - size grains and ≈ 200 K for km - size bodies (D'Angelo and Podolak, 2015) </Li> <P> The radial position of the condensation / evaporation front varies over time, as the nebula evolves . Occasionally, the term snow line is also used to represent the present distance at which water ice can be stable (even under direct sunlight). This current snow line distance is different from the formation snow line distance during the formation of the Solar System, and approximately equals 5 AU . The reason for the difference is that during the formation of the Solar System, the solar nebula was an opaque cloud where temperatures were lower close to the Sun, and the Sun itself was less energetic . After formation, the ice got buried by infalling dust and it has remained stable a few meters below the surface . If ice within 5 AU is exposed, e.g. by a crater, then it sublimates on short timescales . However, out of direct sunlight ice can remain stable on the surface of asteroids (and the Moon) if it is located in permanently shadowed craters, where temperature may remain very low over the age of the Solar System (e.g. 30--40 K on the Moon). </P> <P> Observations of the asteroid belt, located between Mars and Jupiter, suggest that the water snow line during formation of the Solar System was located within this region . The outer asteroids are icy C - class objects (e.g. Abe et al. 2000; Morbidelli et al. 2000) whereas the inner asteroid belt is largely devoid of water . This implies that when planetesimal formation occurred the snow line was located at around 2.7 AU from the Sun . </P>

Where is the frost line in the solar system