the frost line is located approximately equals 5 au in the solar system.
the frost line is located approximately equals 5 au in the solar system.
where is the frost line in the solar system?
approximately equals 5 au
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).
frost line (astrophysics)
the giant planets (jupiter, saturn, uranus, and neptune) formed further out, beyond the frost line, which is the point between the orbits of mars and jupiter where the material is cool enough for volatile icy compounds to remain solid. the ices that formed the jovian planets were more abundant than the metals and silicates that formed the terrestrial planets, allowing the giant planets to grow massive enough to capture hydrogen and helium, the lightest and most abundant elements. planetesimals beyond the frost line accumulated up to within about 3 million years. today, the four giant planets comprise just under 99% of all the mass orbiting the sun. theorists believe it is no accident that jupiter lies just beyond the frost line. because the frost line accumulated large amounts of water via evaporation from infalling icy material, it created a region of lower pressure that increased the speed of orbiting dust particles and halted their motion toward the sun. in effect, the frost line acted as a barrier that caused material to accumulate rapidly at ~5 au from the sun. this excess material coalesced into a large embryo (or core) on the order of , which began to accumulate an envelope via accretion of gas from the surrounding disc at an ever-increasing rate. once the envelope mass became about equal to the solid core mass, growth proceeded very rapidly, reaching about 150 earth masses ~10 years thereafter and finally topping out at . saturn may owe its substantially lower mass simply to having formed a few million years after jupiter, when there was less gas available to consume.
formation and evolution of the solar system