Frost_line_(astrophysics)

# Frost line (astrophysics)  **Microsim — three.js (Wikitube framework):** *Rock inside, gas and ice outside (Solar System explorer)* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=composition&embed=1" data-title="Rock inside, gas and ice outside (Solar System explorer)"></div> *The Solar System explorer locked on this article's state (`?view=composition`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: press o to hide the orbits and read the split in the body colours alone, rocky inside the thin blue ring near 2.7 AU and gas and ice giants outside it; drag to an edge-on view to see that the ring lies in the plane the planets share; set the speed to 100 years/s and watch the split hold across two and a half centuries.* The **frost line** (also called the **snow line** or **ice line**) is the distance from a young star, in the disc of gas and dust around it, beyond which the temperature is low enough for volatile compounds such as [[Water|water]], ammonia, methane and carbon monoxide to freeze into solid grains.[^jewitt2007] Inside the line those compounds stay in the gas and only rock and metal can build solid bodies; outside it the ices add to the solid material, which is why the frost line is the usual explanation for the division between small rocky planets and giant planets. Every volatile has its own line, because each condenses at its own temperature, so a bare "frost line" normally means the water line.[^oberg2019][^qi2013] The explorer at the top of this page opens on the composition view: the [[Terrestrial_planet|rocky planets]] are coloured one way, the [[Gas_giant|gas giants]] and [[Ice_giant|ice giants]] another, and a thin blue ring marks the frost line at about 2.7 AU, the value inferred for the time when planetesimals formed.[^martin2012] The ring sits between the orbits of [[Mars]] and [[Jupiter]], inside the [[Asteroid_belt|asteroid belt]]. ## Location Where the line falls depends on the temperature at which water ice condenses at the low pressures of a protoplanetary nebula, and on the model of the nebula used to compute the temperature at each distance. The answers cluster between about 2.7 and 3.2 [[Astronomical_unit|AU]] for the young Solar System. Chushiro Hayashi's 1981 minimum-mass nebula places the water line where the temperature falls to 170 K, at 2.7 AU.[^hayashi1981] Podolak and Zucker, using a disc heated by accretion as well as by the young Sun, found a condensation temperature of 143 K to 150 K and a line between about 3.0 and 3.2 AU.[^podolak2004] Martin and Livio's model of an evolving disc gives about 3.1 AU.[^martin2012] The condensation temperature also depends on the size of the solid that has to survive: D'Angelo and Podolak estimate about 150 K for micrometre-sized grains and about 200 K for kilometre-sized bodies.[^dangelo2015] The line is not fixed in a given system either. As a disc evolves, its heating by accretion falls and the star's luminosity changes, so the line moves; for a star of one solar mass, Zhang and Jin find that it can reach about 17.4 AU before moving back inward.[^zhang2015] A number such as 2.7 AU is therefore the position at one stage of the disc's evolution, not a permanent property of the star. | Estimate | Temperature | Distance | Source | |---|---|---|---| | Minimum-mass solar nebula | 170 K | 2.7 AU | Hayashi 1981[^hayashi1981] | | Accretion-heated disc | 143–150 K | 3.0–3.2 AU | Podolak and Zucker 2004[^podolak2004] | | Evolving disc | — | 3.1 AU | Martin and Livio 2012[^martin2012] | | Micrometre grains / kilometre bodies | ≈150 K / ≈200 K | — | D'Angelo and Podolak 2015[^dangelo2015] | ## Current versus formation frost line Two different quantities go by the same name. The formation frost line is where water froze in the nebula while the planets were growing. The present-day frost line is the distance at which exposed water ice can survive today, heated by a far brighter Sun and no longer shaded by the dusty nebula; in the present Solar System that distance is about 5 AU.[^jewitt2007] The two differ because the early disc was opaque, so the regions near the young, less luminous Sun were colder than the same distances are now.[^jewitt2007] The asteroid belt records where the formation line lay. Asteroids in its outer part are dark, carbon-rich bodies that carry water-bearing minerals, while the inner belt is largely dry, which places the line inside the belt when planetesimals formed, at about 2.7 AU.[^martin2012] [[Ceres_(dwarf_planet)|Ceres]], with a semi-major axis of 2.77 AU, sits almost on that estimate, and its evolution models give it an icy mantle and possibly a liquid layer beneath its crust.[^mccord2005][^obrien2015] Farther out, at an average of 3.1 AU, water ice has been detected directly on the surface of the asteroid 24 Themis.[^campins2010] Ice inside the present-day line can still last where the Sun never reaches it: in permanently shadowed polar craters of the [[Moon]] and of [[Mercury_(planet)|Mercury]], temperatures stay low enough for ice to survive over the age of the Solar System.[^jewitt2007] The explorer draws the formation value, 2.7 AU, as its frost-line ring; the present-day value of about 5 AU, which is close to Jupiter's orbit, is not drawn. ## Planet formation Beyond the frost line, water ice joins rock and metal as solid building material. Hydrogen and oxygen are far more abundant in the nebula than silicon, magnesium and iron, so the amount of solid mass available to build planetesimals rises sharply at the line, and cores can grow large and fast enough to capture hydrogen and helium from the surrounding gas before the gas disperses. That is the standard account of why the frost line separates the terrestrial planets from the giant planets in the Solar System.[^kaufmann1987] Jupiter, the first planet beyond the line, is also the most massive. Giant planets found close to other stars, the so-called hot Jupiters, do not overturn this account: they are thought to have formed beyond their stars' frost lines and to have migrated inward afterwards through interactions with their discs.[^chambers2007][^dangelo2010] [[Earth]], which formed well inside the line, is too small to have gathered a massive envelope, but it is massive enough to keep water vapour; its ammonia and methane are scarce today because they are unstable in an oxygen-rich atmosphere. The line may also set where asteroid belts form. Martin and Livio, working from the temperatures of warm dust around about 90 stars, found that the dust, and so the likely asteroid belts, lies close to each star's frost line, with a giant planet just outside it disrupting planet formation inward of its orbit.[^nasa2012] Owen's models suggest a mechanism for narrow rings of dust near the line: the frost line can be thermally unstable on timescales of 1,000 to 10,000 years, depositing solids in periodic, narrow bands.[^owen2020] ## See also - [[Protoplanetary_disk]] - [[Formation_and_evolution_of_the_Solar_System]] - [[Habitable_zone]] - [[Asteroid_belt]] - [[Gas_giant]] · [[Ice_giant]] · [[Terrestrial_planet]] ## References [^jewitt2007]: Jewitt, D.; Chizmadia, L.; Grimm, R.; Prialnik, D. (2007). "Water in the small bodies of the Solar System". In Reipurth, B.; Jewitt, D.; Keil, K. (eds.), *Protostars and Planets V*. University of Arizona Press, pp. 863–878. ISBN 978-0-8165-2654-3. http://www.ifa.hawaii.edu/~meech/a740/2006/spring/papers/PPV2006.pdf [^oberg2019]: Öberg, K. I.; Wordsworth, R. (2019). "Jupiter's composition suggests its core assembled exterior to the N₂ snowline". *The Astronomical Journal* 158: 194. https://doi.org/10.3847/1538-3881/ab46a8 [^qi2013]: Qi, C.; Öberg, K. I.; Wilner, D. J.; et al. (2013). "Imaging of the CO snow line in a solar nebula analog". *Science* 341: 630–632. https://doi.org/10.1126/science.1239560 [^hayashi1981]: Hayashi, C. (1981). "Structure of the solar nebula, growth and decay of magnetic fields and effects of magnetic and turbulent viscosities on the nebula". *Progress of Theoretical Physics Supplement* 70: 35–53. https://doi.org/10.1143/PTPS.70.35 [^podolak2004]: Podolak, M.; Zucker, S. (2004). "A note on the snow line in protostellar accretion disks". *Meteoritics & Planetary Science* 39: 1859–1868. https://doi.org/10.1111/j.1945-5100.2004.tb00081.x [^martin2012]: Martin, R. G.; Livio, M. (2012). "On the evolution of the snow line in protoplanetary discs". *Monthly Notices of the Royal Astronomical Society: Letters* 425: L6–L9. https://doi.org/10.1111/j.1745-3933.2012.01290.x [^dangelo2015]: D'Angelo, G.; Podolak, M. (2015). "Capture and evolution of planetesimals in circumjovian disks". *The Astrophysical Journal* 806: 203. https://doi.org/10.1088/0004-637X/806/2/203 [^zhang2015]: Zhang, Y.; Jin, L. (2015). "The evolution of the snow line in a protoplanetary disk". *The Astrophysical Journal* 802: 58. https://doi.org/10.1088/0004-637X/802/1/58 [^mccord2005]: McCord, T. B.; Sotin, C. (2005). "Ceres: Evolution and current state". *Journal of Geophysical Research: Planets* 110: E05009. https://doi.org/10.1029/2004JE002244 [^obrien2015]: O'Brien, D. P.; Travis, B. J.; Feldman, W. C.; et al. (2015). "The potential for volcanism on Ceres due to crustal thickening and pressurization of a subsurface ocean". *46th Lunar and Planetary Science Conference*, abstract 2831. http://www.hou.usra.edu/meetings/lpsc2015/pdf/2831.pdf [^campins2010]: Campins, H.; Hargrove, K.; Pinilla-Alonso, N.; et al. (2010). "Water ice and organics on the surface of the asteroid 24 Themis". *Nature* 464: 1320–1321. https://doi.org/10.1038/nature09029 [^kaufmann1987]: Kaufmann, W. J. (1987). *Discovering the Universe*. W. H. Freeman and Company, p. 94. ISBN 978-0-7167-1784-3. https://archive.org/details/discoveringunive00kauf/page/94 [^chambers2007]: Chambers, J. (2007). "Planet formation with Type I and Type II migration". *AAS/Division of Dynamical Astronomy Meeting* 38. Bibcode 2007DDA....38.0604C. [^dangelo2010]: D'Angelo, G.; Durisen, R. H.; Lissauer, J. J. (2010). "Giant planet formation". In Seager, S. (ed.), *Exoplanets*. University of Arizona Press, pp. 319–346. ISBN 978-0-8165-2945-2. [^nasa2012]: NASA (November 1, 2012). "Asteroid belts of just the right size are friendly to life". http://www.nasa.gov/mission_pages/hubble/science/right-sized-belts.html [^owen2020]: Owen, J. E. (2020). "Snow-lines can be thermally unstable". *Monthly Notices of the Royal Astronomical Society* 495: 3160–3174. https://doi.org/10.1093/mnras/staa1309 ## External links - Min, M.; Dullemond, C. P.; Kama, M.; Dominik, C. (2011). "The thermal structure and the location of the snow line in the protosolar nebula". *Icarus* 212: 416–426. https://doi.org/10.1016/j.icarus.2010.12.002 - Sasselov, D. D.; Lecar, M. (2000). "On the snow line in dusty protoplanetary disks". *The Astrophysical Journal* 528: 995–998. https://doi.org/10.1086/308209 ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Frost_line_(astrophysics)) : [Wikitube](https://en.wikitube.io/wiki/Frost_line_(astrophysics)) · pinned revision [1372525572](https://en.wikipedia.org/w/index.php?oldid=1372525572) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Solar_System]]. --- *Solar System portal child articles, wave 1 · 2026-09-18 · drafted · row SOL-003 · explorer state `?view=composition`.*