Protoplanetary_disk - Wikiparency

# Protoplanetary disk  **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: drag the scene until it is seen edge-on and notice how thin a plane the eight planets occupy, the imprint of the disc they formed in; press l to show the labels and pick out the rocky planets inside the frost line and the gas and ice giants outside it; then press o to hide the orbits and compare the two groups by colour alone.* A **protoplanetary disk** is a rotating disc of dense gas and dust around a newly formed star, such as a T Tauri star or a Herbig Ae/Be star, from which planets can form.[^armitage2011] It resembles an accretion disc, and matter does flow through it onto the star, but it is cooler and far more massive in dust, and it is where the solid building blocks of planets are assembled.[^pringle1981] Discs lit and eroded by the radiation of nearby hot stars, as in the Orion Nebula, are called proplyds.[^odell1996] This article covers how such discs form from a collapsing cloud and how long they last, how they turn into a [[Planetary_system|planetary system]], the gas-poor debris discs that follow them, and the proposal that organic molecules important for life were made in them. The explorer at the top of this page opens on the composition view of the Solar System, the finished product of one such disc: [[Terrestrial_planet|rocky planets]] inside the [[Frost_line_(astrophysics)|frost line]] and giant planets beyond it, all orbiting close to one plane. ## Formation Stars form from molecular clouds, mostly of molecular [[Hydrogen|hydrogen]]. When a region becomes dense enough, its [[Gravity|gravity]] overwhelms its pressure and it collapses. The random motions of the gas largely cancel out, leaving the net rotation of the collapsing region, and because [[Angular_momentum|angular momentum]] is conserved that rotation speeds up as the region shrinks: at fixed angular momentum the rotation speed scales roughly as 1/r, so material falling from 10,000 AU to 100 AU spins about a hundred times faster (derived). Rotation resists collapse only in the directions perpendicular to the spin axis; along the axis nothing stops the infall, so the cloud flattens into a disc, supported vertically by gas pressure.[^pringle1981] The initial collapse takes more than 100,000 years, after which the young star becomes visible as a T Tauri star while gas from the disc keeps falling onto it for up to about 10 million years.[^mamajek2004] Surveys of young clusters show the fraction of stars with discs falling steadily with age, over a characteristic time of a few million years.[^mamajek2009] A few discs last much longer: an accreting disc around the binary T Tauri star St 34 is about 25 million years old.[^white2005] Discs are thin. Their thickness is set by the ratio of the gas's sound speed to its orbital speed; at 1 AU, gas at about 300 K has a sound speed of about 1 km/s against an orbital speed of 29.8 km/s, so the disc is only about 3% as thick as its radius there (derived).[^armitage2011][^nasa-fs] Their mass is also much smaller than that of the star, and it is mostly gas, with dust about a hundredth of it.[^armitage2011] Radii reach several hundred AU, and only the innermost regions are hotter than about 1,000 K.[^armitage2011] The Hubble Space Telescope has imaged many discs and proplyds in the Orion Nebula, seen in silhouette against the glowing gas.[^odell1996][^ricci2008] Gas must lose angular momentum to fall inward, and the main mechanism proposed is turbulence driven by the magnetorotational instability, which arises when a weak magnetic field threads differentially rotating, ionised gas ([[Magnetohydrodynamics|magnetohydrodynamics]]).[^balbus1991] Dust shields the mid-plane from ionising radiation, so the instability may operate only in the disc's surface layers, an active zone surrounding a quiescent dead zone in which accretion slows and matter can pile up.[^gammie1996] ## Planetary system The nebular hypothesis describes how such a disc becomes a [[Planetary_system|planetary system]]. Dust and ice grains collide and stick, electrostatic forces helping at the smallest sizes and gravity at larger ones, until they build planetesimals kilometres across. This growth competes with processes that remove material: gas accreting onto the star, driven by the disc's internal stresses, and gas driven out by the star's wind and radiation.[^lissauer2009] Planetesimals are the building blocks of both [[Terrestrial_planet|terrestrial planets]] and [[Gas_giant|gas giants]]; a giant planet's core forms from them and, once massive enough, captures an envelope of gas before the disc disperses.[^lissauer2009][^dangelo2014] The same process repeats on a smaller scale. The large regular moons of [[Jupiter]], [[Saturn]] and [[Uranus]] are thought to have formed in circumplanetary discs, miniature versions of the disc around the Sun; the [[Galilean_moons|Galilean moons]] orbit in Jupiter's equatorial plane, as the planets orbit near the Sun's.[^canup2009][^dangelo2015] A thin disc produces a flat system, and the Solar System is flat: apart from [[Mercury_(planet)|Mercury]] at 7.0° and [[Venus]] at 3.4°, every planet's orbit is inclined by less than 2.5° to the ecliptic, the plane of Earth's orbit.[^jpl-t1] The explorer above uses these orbital elements, which is why the planets appear almost in one plane when the scene is turned edge-on. The disc's legacy also shows in the late stages. After the gas was gone the inner few AU still held many Moon- to Mars-sized bodies that collided and merged into the terrestrial planets, and one such collision, between the proto-Earth and a body about the mass of [[Mars]], is thought to have formed the [[Moon]].[^kominami2002][^canup2001] ## Debris disks Many nearby main-sequence stars show infrared emission from dust in excess of what the star itself would give. The first was found in 1984 around Vega by the IRAS satellite, and in the same year the dust around Beta Pictoris was imaged directly as an edge-on disc.[^aumann1984][^smith1984] These gas-poor discs, now known around stars from about ten million to several billion years old, are called debris discs.[^wyatt2008][^hughes2018] The dust in them cannot be left over from the star's birth. Small grains are removed quickly: radiation pressure blows the smallest out of the system, collisions grind others down, and Poynting–Robertson drag, the loss of orbital angular momentum a grain suffers by absorbing and re-emitting sunlight, makes the rest spiral inward.[^burns1979] For a grain whose radiation-pressure force is half the star's gravity, orbiting a Sun-like star at 1 AU, the drag timescale is about 400 / 0.5 ≈ 800 years (derived), negligible beside the star's age.[^wyatt2008] The dust must therefore be replenished continually, by collisions between planetesimals: asteroids and comets.[^wyatt2008] Debris discs are thus not protoplanetary but a later stage, extrasolar analogues of the [[Asteroid_belt|asteroid belt]] and the [[Kuiper_belt|Kuiper belt]]. Their structures, such as rings, sharp edges, warps and clumps, can reveal unseen planets that sculpt them, much as Neptune shapes the Kuiper belt.[^hughes2018] Five debris discs recovered in 2014 from archival Hubble images, reprocessed with improved techniques, raised the number imaged in scattered light from 18 to 23.[^nasa2014] ## Relation to abiogenesis The disc may also be where some of the ingredients of life were first assembled. Computer models by Fred Ciesla and Scott Sandford follow icy dust grains as turbulence in the solar nebula carries them between the cold, dark mid-plane and the disc's surface layers, where ultraviolet light breaks molecules in the ice apart and warming lets the fragments recombine. Their simulations find that complex organic molecules can form this way on grains that later became part of planetesimals, before the Earth existed.[^ciesla2012][^moskowitz2012] If the process works as modelled, it is not specific to the Solar System: any disc with icy grains, turbulence and a young star's ultraviolet light could make the same compounds, so planets forming around other stars would also inherit organic material from their discs.[^moskowitz2012] The proposal does not by itself explain how life began, which requires chemistry on a planet after those compounds were delivered; the disc models address only where some of the starting materials came from. The same icy grains beyond the [[Frost_line_(astrophysics)|frost line]] also carried [[Water|water]], which the formation models of the Solar System deliver to the inner planets through planetesimals scattered from the outer [[Asteroid_belt|asteroid belt]].[^raymond2007] ## Gallery Direct images of protoplanetary discs have become common only since the mid-2010s. In 2014 the Atacama Large Millimeter/submillimeter Array (ALMA) imaged the disc around HL Tauri, a star about 450 light-years away and no more than a million years old, at an angular resolution of 35 milliarcseconds; the image shows a series of concentric bright rings separated by dark gaps, widely read as the marks of forming planets.[^eso2014][^alma2015] In 2016 ALMA observed V883 Orionis during an outburst that had heated its disc and pushed the water snow line, normally about 3 AU from such a star, out to about 40 AU, where it could be resolved for the first time.[^eso2016][^cieza2016] Other images show the variety of disc geometry. The Hubble Space Telescope photographed a vast shadow cast on the Serpens Nebula by the disc around the young star HBC 672, about 1,300 light-years away; the disc itself is too small to resolve, but its shadow spans roughly 200 times the diameter of the Solar System.[^esa2018] ALMA observations of GW Orionis, a system of three stars, show a disc broken into misaligned, tilted rings, evidence of the gravitational interaction between a multiple star and its circumstellar material.[^bi2020] Hubble's surveys of the Orion Nebula show many young stars surrounded by proplyds whose outer layers are being evaporated by the nebula's hot stars.[^ricci2008] ## See also - [[Formation_and_evolution_of_the_Solar_System]] - [[Frost_line_(astrophysics)]] - [[Planetary_system]] - [[Interplanetary_dust_cloud]] - Accretion disk · Debris disk · Herbig–Haro object · Nebular hypothesis ## References [^armitage2011]: Armitage, P. J. (2011). "Dynamics of protoplanetary disks". *Annual Review of Astronomy and Astrophysics* 49: 195–236. https://doi.org/10.1146/annurev-astro-081710-102521 [^pringle1981]: Pringle, J. E. (1981). "Accretion discs in astrophysics". *Annual Review of Astronomy and Astrophysics* 19: 137–160. https://doi.org/10.1146/annurev.aa.19.090181.001033 [^odell1996]: O'Dell, C. R.; Wong, K. (1996). "Hubble Space Telescope mapping of the Orion Nebula. I. A survey of stars and compact objects". *The Astronomical Journal* 111: 846. https://doi.org/10.1086/117832 [^mamajek2004]: Mamajek, E. E.; Meyer, M. R.; Hinz, P. M.; et al. (2004). "Constraining the lifetime of circumstellar disks in the terrestrial planet zone: a mid-infrared survey of the 30 Myr old Tucana–Horologium association". *The Astrophysical Journal* 612: 496–510. https://doi.org/10.1086/422550 [^mamajek2009]: Mamajek, E. E. (2009). "Initial conditions of planet formation: lifetimes of primordial disks". *AIP Conference Proceedings* 1158: 3–10. https://doi.org/10.1063/1.3215910 [^white2005]: White, R. J.; Hillenbrand, L. A. (2005). "A long-lived accretion disk around a lithium-depleted binary T Tauri star". *The Astrophysical Journal* 621: L65–L68. https://doi.org/10.1086/428752 [^nasa-fs]: NASA NSSDCA. "Planetary Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/ (fetched 2026-09-18). [^ricci2008]: Ricci, L.; Robberto, M.; Soderblom, D. R. (2008). "The Hubble Space Telescope/Advanced Camera for Surveys atlas of protoplanetary disks in the Great Orion Nebula". *The Astronomical Journal* 136: 2136–2151. https://doi.org/10.1088/0004-6256/136/5/2136 [^balbus1991]: Balbus, S. A.; Hawley, J. F. (1991). "A powerful local shear instability in weakly magnetized disks. I. Linear analysis. II. Nonlinear evolution". *The Astrophysical Journal* 376: 214–233. https://doi.org/10.1086/170270 [^gammie1996]: Gammie, C. F. (1996). "Layered accretion in T Tauri disks". *The Astrophysical Journal* 457: 355. https://doi.org/10.1086/176735 [^lissauer2009]: Lissauer, J. J.; Hubickyj, O.; D'Angelo, G.; Bodenheimer, P. (2009). "Models of Jupiter's growth incorporating thermal and hydrodynamic constraints". *Icarus* 199: 338–350. https://doi.org/10.1016/j.icarus.2008.10.004 [^dangelo2014]: D'Angelo, G.; Weidenschilling, S. J.; Lissauer, J. J.; Bodenheimer, P. (2014). "Growth of Jupiter: enhancement of core accretion by a voluminous low-mass envelope". *Icarus* 241: 298–312. https://doi.org/10.1016/j.icarus.2014.06.029 [^canup2009]: Canup, R. M.; Ward, W. R. (2009). "Origin of Europa and the Galilean satellites". In Pappalardo, R. T.; McKinnon, W. B.; Khurana, K. (eds.), *Europa*. University of Arizona Press, p. 59. ISBN 978-0-8165-2844-8. [^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 [^jpl-t1]: JPL Solar System Dynamics. "Approximate positions of the planets", Table 1. https://ssd.jpl.nasa.gov/planets/approx_pos.html [^kominami2002]: Kominami, J.; Ida, S. (2002). "The effect of tidal interaction with a gas disk on formation of terrestrial planets". *Icarus* 157: 43–56. https://doi.org/10.1006/icar.2001.6811 [^canup2001]: Canup, R. M.; Asphaug, E. (2001). "Origin of the Moon in a giant impact near the end of the Earth's formation". *Nature* 412: 708–712. https://doi.org/10.1038/35089010 [^aumann1984]: Aumann, H. H.; Beichman, C. A.; Gillett, F. C.; et al. (1984). "Discovery of a shell around Alpha Lyrae". *The Astrophysical Journal* 278: L23–L27. https://doi.org/10.1086/184214 [^smith1984]: Smith, B. A.; Terrile, R. J. (1984). "A circumstellar disk around β Pictoris". *Science* 226: 1421–1424. https://doi.org/10.1126/science.226.4681.1421 [^wyatt2008]: Wyatt, M. C. (2008). "Evolution of debris disks". *Annual Review of Astronomy and Astrophysics* 46: 339–383. https://doi.org/10.1146/annurev.astro.45.051806.110525 [^hughes2018]: Hughes, A. M.; Duchêne, G.; Matthews, B. C. (2018). "Debris disks: structure, composition, and variability". *Annual Review of Astronomy and Astrophysics* 56: 541–591. https://doi.org/10.1146/annurev-astro-081817-052035 [^burns1979]: Burns, J. A.; Lamy, P. L.; Soter, S. (1979). "Radiation forces on small particles in the solar system". *Icarus* 40: 1–48. https://doi.org/10.1016/0019-1035(79)90050-2 [^nasa2014]: Harrington, J. D.; Villard, R. (24 April 2014). "Release 14-114: Astronomical forensics uncover planetary disks in NASA's Hubble archive". NASA. http://www.nasa.gov/press/2014/april/astronomical-forensics-uncover-planetary-disks-in-nasas-hubble-archive [^ciesla2012]: Ciesla, F. J.; Sandford, S. A. (2012). "Organic synthesis via irradiation and warming of ice grains in the solar nebula". *Science* 336: 452–454. https://doi.org/10.1126/science.1217291 [^moskowitz2012]: Moskowitz, C. (29 March 2012). "Life's building blocks may have formed in dust around young Sun". *Space.com*. http://www.space.com/15089-life-building-blocks-young-sun-dust.html [^raymond2007]: Raymond, S. N.; Quinn, T.; Lunine, J. I. (2007). "High-resolution simulations of the final assembly of Earth-like planets. 2. Water delivery and planetary habitability". *Astrobiology* 7: 66–84. https://doi.org/10.1089/ast.2006.06-0126 [^eso2014]: ESO (6 November 2014). "Revolutionary ALMA image reveals planetary genesis" (eso1436). https://www.eso.org/public/news/eso1436/ [^alma2015]: ALMA Partnership; Brogan, C. L.; Pérez, L. M.; Hunter, T. R.; et al. (2015). "The 2014 ALMA Long Baseline Campaign: first results from high angular resolution observations toward the HL Tau region". *The Astrophysical Journal Letters* 808: L3. https://doi.org/10.1088/2041-8205/808/1/L3 [^eso2016]: ESO (13 July 2016). "Stellar outburst brings water snow line into view" (eso1626). https://www.eso.org/public/news/eso1626/ [^cieza2016]: Cieza, L. A.; Casassus, S.; Tobin, J.; et al. (2016). "Imaging the water snow-line during a protostellar outburst". *Nature* 535: 258–261. https://doi.org/10.1038/nature18612 [^esa2018]: ESA/Hubble (2018). "Hubble reveals cosmic Bat Shadow in the Serpent's Tail" (heic1819). https://esahubble.org/news/heic1819/ [^bi2020]: Bi, J.; van der Marel, N.; Dong, R.; et al. (2020). "GW Ori: interactions between a triple-star system and its circumtriple disk in action". *The Astrophysical Journal Letters* 895: L18. https://doi.org/10.3847/2041-8213/ab8eb4 ## Further reading - Armitage, P. J. (2020). *Astrophysics of Planet Formation* (2nd ed.). Cambridge University Press. - Williams, J. P.; Cieza, L. A. (2011). "Protoplanetary disks and their evolution". *Annual Review of Astronomy and Astrophysics* 49: 67–117. https://doi.org/10.1146/annurev-astro-081710-102548 ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Protoplanetary_disk) : [Wikitube](https://en.wikitube.io/wiki/Protoplanetary_disk) · pinned revision [1372528294](https://en.wikipedia.org/w/index.php?oldid=1372528294) · 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-034 · explorer state `?view=composition`.*