Grand_tack_hypothesis

# Grand tack hypothesis  **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 l to show the labels and find Mars, the small rocky planet whose low mass the grand tack was proposed to explain, and the asteroid belt beyond it; drag to a view from above and compare Jupiter's present orbit near 5.2 AU with Earth's, remembering that the hypothesis brings Jupiter in to about 1.5 AU, just outside Mars's orbit; then press o to hide the orbits and read the rock-inside, giants-outside split by colour.* The **grand tack hypothesis** proposes that [[Jupiter]] formed at about 3.5 AU from the [[Sun]], migrated inward through the gas disc to about 1.5 AU, and then reversed direction after capturing [[Saturn]] in an orbital resonance, moving back out until it stopped near its present orbit at 5.2 AU.[^zubritsky][^walsh2011] The name comes from sailing: a boat heading into the wind makes progress by tacking, turning from one course to the opposite.[^zubritsky] The hypothesis was introduced in 2011 by Kevin Walsh, Alessandro Morbidelli and colleagues to solve two problems at once: the small mass of [[Mars]] and the structure of the [[Asteroid_belt|asteroid belt]].[^walsh2011] By sweeping in and out, Jupiter would have truncated the disc of planetesimals near 1 AU, leaving little material in the Mars region, and crossed the asteroid belt twice, emptying it and mixing into it bodies from both inside and outside its own original orbit.[^beatty2010][^sanders2011] Later work suggested that the same migration may also explain why the Solar System has no planets orbiting closer than [[Mercury_(planet)|Mercury]].[^batygin2015] The explorer at the top of this page shows the end state that the grand tack is meant to produce: small [[Terrestrial_planet|rocky planets]] inside the [[Frost_line_(astrophysics)|frost line]], Mars the smallest of those beyond Earth, and the [[Gas_giant|gas giants]] far outside. ## Description In the hypothesis Jupiter forms near the ice line, at roughly 3.5 AU, while the gas disc is still present.[^walsh2011] A planet massive enough to open a gap in the gas becomes locked to the disc's slow inward flow, a process known as type II migration; left alone, it would carry Jupiter close to the Sun, as appears to have happened to the hot Jupiters found around other stars.[^fesenmaier2015] Saturn, less massive, migrates inward faster, until it catches up with Jupiter and is captured in their 3:2 mean-motion [[Resonance|resonance]], in which Jupiter makes three orbits for every two of Saturn's.[^walsh2011] The two planets then clear a common gap in the disc.[^morbidelli2007] A shared gap changes the balance of forces. A planet's migration is set by the difference between the torques exerted on it by the gas inside its orbit, which pushes it outward, and the gas outside, which pulls it inward. Because Saturn partly clears the outer side of the gap, the inner disc's torque on Jupiter comes to dominate and the pair begin to move outward together.[^morbidelli2007][^masset2001] The outward motion is sustained because gas can flow through the shared gap from the outer disc to the inner one, exchanging angular momentum with the planets on the way and keeping the inner disc supplied.[^masset2001][^morbidelli2007] In the grand tack this reversal is assumed to happen when Jupiter reaches about 1.5 AU, and the outward migration continues until the planets reach a configuration where the torques balance or until the gas disperses, leaving Jupiter near its present orbit.[^walsh2011][^pierens2011] The distances translate into large changes in orbital period. By [[Kepler's_laws_of_planetary_motion|Kepler's third law]] the period in years is the semi-major axis in AU raised to the power 1.5, so at 3.5 AU Jupiter would have orbited in about 6.5 years, at 1.5 AU in about 1.8 years, and at its present 5.20 AU it takes about 11.9 years (derived).[^jpl-t1] At its closest, Jupiter would thus have orbited only slightly farther out than Mars does today, at 1.52 AU.[^jpl-t1] ## Scope The hypothesis addresses the mass of Mars, the composition and orbits of the asteroid belt, the absence of close-in planets, and several later-developed consequences. ### Mars problem Simulations of terrestrial-planet formation that begin with planetesimals spread evenly through the inner Solar System tend to produce a planet in the Mars region far heavier than Mars, whose mass is only 0.107 that of Earth.[^raymond2009][^nasa-fs] This conflict is the "Mars problem". In the grand tack, Jupiter's inward passage herds planetesimals ahead of it into a narrow, dense band inside about 1.0 AU and leaves the region beyond largely empty.[^carter2015][^walsh-swri] Embryos grow quickly in the band and most collide and merge into [[Venus]] and [[Earth]] over 60 to 130 million years.[^jacobson2014] Others are scattered out of the band, where they find little more to accrete and stay small; these become Mars and Mercury.[^hansen2009] Mars's small mass, in this picture, is a consequence of where the material was, not of how it grew. ### Asteroid belt Before Jupiter moved, the asteroid-forming region varied in composition with distance from the Sun: rocky bodies closer in, and more primitive, icy ones beyond the ice line.[^raymond2013] As Jupiter and Saturn move inward, about 15% of the inner, rocky asteroids are thrown outward beyond Saturn.[^beatty2010] On the way back out the planets meet these bodies first and return about 0.5% of the original population inward onto stable orbits; later, crossing the outer region, they scatter about 0.5% of the primitive asteroids into the outer part of the belt.[^walsh2011] The result is a belt of small total mass whose inner part is dominated by rocky S-type asteroids and whose outer part by carbon-rich C-types, as observed, with high eccentricities and inclinations that the later giant-planet instability of the [[Nice_model|Nice model]] can reduce to the present distribution.[^walsh2011][^deienno2016] Some icy asteroids are left on orbits crossing the region where the terrestrial planets were forming, and collisions with them could have delivered [[Water|water]] to the growing planets.[^obrien2014][^matsumura2016] ### Absent super-Earths Many planetary systems contain super-Earths, planets a few times Earth's mass on orbits well inside Mercury's; the Solar System has none. Jupiter's inward migration offers one explanation.[^batygin2015] As Jupiter moves inward it captures planetesimals in its resonances, shrinking their orbits and raising their eccentricities until their collisions become destructive. The debris then spirals toward the Sun under gas drag, and any super-Earths already present would have been caught in resonance with it and dragged into the Sun as well. The present terrestrial planets would then form from the material left behind after Jupiter reversed.[^batygin2015][^astronomynow2015] Other outcomes are possible: debris that reassembles into larger bodies feels less drag, and a disc with an inner cavity would halt migrating planets at its edge.[^raymond2016] If no planets had yet formed close in, the destroyed material might have been fine enough to be blown outward by the strong early solar wind, leaving little to build planets inside Mercury's orbit.[^spalding2018] ### Post-hypothesis developments Later simulations with more realistic discs, including viscous heating and the migration of the embryos themselves, found that a tack at 1.5 AU puts the largest terrestrial planet near Venus's orbit rather than Earth's, and that a tack at 2.0 AU matches the Solar System better.[^brasser2016] Including fragmentation in hit-and-run collisions also improves the terrestrial planets' orbits: the extra small fragments damp eccentricities and inclinations, concentrate more mass in Venus and Earth, and lengthen their formation relative to Mars.[^clement2019] The migration may be recorded in meteorites. CB chondrites are metal-rich meteorites whose iron–nickel nodules crystallised from vapour produced by impacts about 4.8 ± 0.3 million years after the first solids; vaporising metal needs impacts faster than about 18 km/s, well above the 12.2 km/s maximum of standard accretion models. Jupiter's passage through the asteroid belt would excite orbits enough to produce such speeds for about half a million years, dating the migration to 4.5–5 million years after the Solar System formed.[^johnson2016] The timing may also explain why [[Titan_(moon)|Titan]] has a thick atmosphere and [[Ganymede_(moon)|Ganymede]] and [[Callisto_(moon)|Callisto]] do not: moons formed before the tack would have lost their volatiles as Jupiter moved closer to the Sun, while Titan must have formed afterwards.[^heller2015] Encounters with other embryos after Mars was scattered from the band could have disturbed the disc of material around it, explaining why the [[Moons_of_Mars|moons of Mars]] are so small.[^hansen2018] ## Potential problems Mars may not share the composition of Earth and Venus. If it does not, most of its growth must have happened outside the narrow band the grand tack creates, since planets built inside the band end with similar compositions. An early tack could produce a distinct Mars if the embryo that became Mars was scattered outward and then back in, like the asteroids, but the chance of that is only about 2%.[^brasser2017] The migration mechanism itself has been questioned. Studies of Jupiter and Saturn converging in a dissipating nebula find that they are unlikely to be captured in the 3:2 resonance: Saturn migrates more slowly than assumed and is captured instead in the 2:1 resonance.[^dangelo2012][^chametla2020][^griveaud2023] Capture in the 2:1 resonance does not usually reverse the migration; particular disc structures that do drive the pair outward tend to excite Jupiter's and Saturn's eccentricities to two or three times their actual values.[^pierens2014] If the gas is such that Saturn opens a deeper gap, the net torque can turn negative again and the planets resume their inward drift.[^dangelo2012] The hypothesis also ignores continued gas accretion by the two planets. Driving them outward requires a large reservoir of gas near their orbits, but the same gas would feed them, changing their masses and their mass ratio.[^dangelo2012] The dense disc needed for capture in the 3:2 resonance is particularly dangerous, because it can lead to rapid mass growth and planet–planet scattering.[^marzari2013] Gas taken up by the planets also reduces the flow toward the inner disc, weakening the inner torques that push Jupiter outward and possibly ending the outward migration early.[^dangelo2012] ## Alternatives Several other explanations exist for the small mass of Mars. A small Mars may simply be an unlikely but possible outcome: it appears in a small fraction of simulations that start with planetesimals spread through the inner Solar System.[^chambers2013][^fischer2014] The Mars region may have been largely empty from the start, if solids drifted inward before planetesimals formed.[^izidoro2015][^drazkowska2016] An early giant-planet instability, as in the [[Nice_model|Nice model]], could have removed most of the mass from the Mars region before the planet formed.[^clement2018] If the terrestrial planets grew mainly by accreting small pebbles, the process may have become less efficient with distance from the Sun.[^levison2015] Embryos migrating in the gas disc could have converged near 1 AU, forming large planets only there and leaving Mars as a stranded embryo.[^broz2021] Secular resonances sweeping through the region as the gas cleared could have excited orbits so that collisions shattered rather than merged.[^bromley2017] Other proposals address the asteroid belt. The belt may have started nearly empty and been filled by icy planetesimals scattered inward while Jupiter and Saturn accreted their gas, and by rocky ones scattered outward by the growing terrestrial planets; the icy bodies could also have brought water inward.[^raymond2017water][^raymond2017empty] Its orbits could have been excited by chaotic motion of Jupiter and Saturn before the instability, by the instability itself, or by secular resonance sweeping as the nebula dissipated.[^izidoro2016][^deienno2018][^zheng2017] For the missing inner planets, suggestions include an outward migration of Jupiter's core from close to the Sun, discs evolving through winds that let embryos migrate outward, the loss of an early inner generation of planets in destructive collisions, and an inner edge to the planetesimal disc set by where silicates condensed.[^raymond2016][^ogihara2015][^volk2015][^morbidelli2016] A depleted early inner Solar System could also have produced a few small planets of which only [[Mercury_(planet)|Mercury]] survived.[^clement2021] ## See also - [[Formation_and_evolution_of_the_Solar_System]] - [[Nice_model]] - [[Late_Heavy_Bombardment]] - [[Protoplanetary_disk]] - Jumping-Jupiter scenario · Planetary migration ## References [^zubritsky]: Zubritsky, E. "Jupiter's youthful travels redefined Solar System". NASA. https://www.nasa.gov/topics/solarsystem/features/young-jupiter.html [^walsh2011]: Walsh, K. J.; Morbidelli, A.; Raymond, S. N.; O'Brien, D. P.; Mandell, A. M. (2011). "A low mass for Mars from Jupiter's early gas-driven migration". *Nature* 475: 206–209. https://doi.org/10.1038/nature10201 [^beatty2010]: Beatty, K. (16 October 2010). "Our 'new, improved' Solar System". *Sky & Telescope*. http://www.skyandtelescope.com/astronomy-news/our-new-improved-solar-system/ [^sanders2011]: Sanders, R. (23 August 2011). "How did Jupiter shape our Solar System?". *Universe Today*. http://www.universetoday.com/88374/how-did-jupiter-shape-our-solar-system/ [^batygin2015]: Batygin, K.; Laughlin, G. (2015). "Jupiter's decisive role in the inner Solar System's early evolution". *Proceedings of the National Academy of Sciences* 112: 4214–4217. https://doi.org/10.1073/pnas.1423252112 [^fesenmaier2015]: Fesenmaier, K. (23 March 2015). "New research suggests Solar System may have once harbored super-Earths". Caltech. http://www.caltech.edu/news/new-research-suggests-solar-system-may-have-once-harbored-super-earths-46017 [^morbidelli2007]: Morbidelli, A.; Crida, A. (2007). "The dynamics of Jupiter and Saturn in the gaseous protoplanetary disk". *Icarus* 191: 158–171. https://doi.org/10.1016/j.icarus.2007.04.001 [^masset2001]: Masset, F.; Snellgrove, M. (2001). "Reversing type II migration: resonance trapping of a lighter giant protoplanet". *Monthly Notices of the Royal Astronomical Society* 320: L55–L59. https://doi.org/10.1046/j.1365-8711.2001.04159.x [^pierens2011]: Pierens, A.; Raymond, S. N. (2011). "Two phase, inward-then-outward migration of Jupiter and Saturn in the gaseous solar nebula". *Astronomy & Astrophysics* 533: A131. https://doi.org/10.1051/0004-6361/201117451 [^jpl-t1]: JPL Solar System Dynamics. "Approximate positions of the planets", Table 1. https://ssd.jpl.nasa.gov/planets/approx_pos.html [^raymond2009]: Raymond, S. N.; O'Brien, D. P.; Morbidelli, A.; Kaib, N. A. (2009). "Building the terrestrial planets: constrained accretion in the inner Solar System". *Icarus* 203: 644–662. https://doi.org/10.1016/j.icarus.2009.05.016 [^nasa-fs]: NASA NSSDCA. "Planetary Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/ (fetched 2026-09-18). [^carter2015]: Carter, P. J.; Leinhardt, Z. M.; Elliott, T.; Walter, M. J.; Stewart, S. T. (2015). "Compositional evolution during rocky protoplanet accretion". *The Astrophysical Journal* 813: 72. https://doi.org/10.1088/0004-637X/813/1/72 [^walsh-swri]: Walsh, K. "The Grand Tack". Southwest Research Institute. http://www.boulder.swri.edu/~kwalsh/GrandTack.html [^jacobson2014]: Jacobson, S. A.; Morbidelli, A. (2014). "Lunar and terrestrial planet formation in the Grand Tack scenario". *Philosophical Transactions of the Royal Society A* 372: 20130174. https://doi.org/10.1098/rsta.2013.0174 [^hansen2009]: Hansen, B. M. S. (2009). "Formation of the terrestrial planets from a narrow annulus". *The Astrophysical Journal* 703: 1131–1140. https://doi.org/10.1088/0004-637X/703/1/1131 [^raymond2013]: Raymond, S. (2 August 2013). "The Grand Tack". *PlanetPlanet*. http://planetplanet.net/2013/08/02/the-grand-tack/ [^deienno2016]: Deienno, R.; Gomes, R. S.; Walsh, K. J.; Morbidelli, A.; Nesvorný, D. (2016). "Is the Grand Tack model compatible with the orbital distribution of main belt asteroids?". *Icarus* 272: 114–124. https://doi.org/10.1016/j.icarus.2016.02.043 [^obrien2014]: O'Brien, D. P.; Walsh, K. J.; Morbidelli, A.; Raymond, S. N.; Mandell, A. M. (2014). "Water delivery and giant impacts in the 'Grand Tack' scenario". *Icarus* 239: 74–84. https://doi.org/10.1016/j.icarus.2014.05.009 [^matsumura2016]: Matsumura, S.; Brasser, R.; Ida, S. (2016). "Effects of dynamical evolution of giant planets on the delivery of atmophile elements during terrestrial planet formation". *The Astrophysical Journal* 818: 15. https://doi.org/10.3847/0004-637X/818/1/15 [^astronomynow2015]: *Astronomy Now* (25 March 2015). "Wandering Jupiter swept away super-Earths, creating our unusual Solar System". https://astronomynow.com/2015/03/25/wandering-jupiter-swept-away-super-earths-creating-our-unusual-solar-system/ [^raymond2016]: Raymond, S. N.; Izidoro, A.; Bitsch, B.; Jacobson, S. A. (2016). "Did Jupiter's core form in the innermost parts of the Sun's protoplanetary disc?". *Monthly Notices of the Royal Astronomical Society* 458: 2962–2972. https://doi.org/10.1093/mnras/stw431 [^spalding2018]: Spalding, C. (2018). "The primordial solar wind as a sculptor of terrestrial planet formation". *The Astrophysical Journal Letters* 869: L17. https://doi.org/10.3847/2041-8213/aaf478 [^brasser2016]: Brasser, R.; Matsumura, S.; Ida, S.; Mojzsis, S. J.; Werner, S. C. (2016). "Analysis of terrestrial planet formation by the Grand Tack model: system architecture and tack location". *The Astrophysical Journal* 821: 75. https://doi.org/10.3847/0004-637X/821/2/75 [^clement2019]: Clement, M. S.; Kaib, N. A.; Raymond, S. N.; Chambers, J. E.; Walsh, K. J. (2019). "The early instability scenario: terrestrial planet formation during the giant planet instability, and the effect of collisional fragmentation". *Icarus* 321: 778–790. https://doi.org/10.1016/j.icarus.2018.12.033 [^johnson2016]: Johnson, B. C.; Walsh, K. J.; Minton, D. A.; Krot, A. N.; Levison, H. F. (2016). "Timing of the formation and migration of giant planets as constrained by CB chondrites". *Science Advances* 2: e1601658. https://doi.org/10.1126/sciadv.1601658 [^heller2015]: Heller, R.; Marleau, G.-D.; Pudritz, R. E. (2015). "The formation of the Galilean moons and Titan in the Grand Tack scenario". *Astronomy & Astrophysics* 579: L4. https://doi.org/10.1051/0004-6361/201526348 [^hansen2018]: Hansen, B. M. S. (2018). "A dynamical context for the origin of Phobos and Deimos". *Monthly Notices of the Royal Astronomical Society* 475: 2452–2466. https://doi.org/10.1093/mnras/stx3361 [^brasser2017]: Brasser, R.; Mojzsis, S. J.; Matsumura, S.; Ida, S. (2017). "The cool and distant formation of Mars". *Earth and Planetary Science Letters* 468: 85–93. https://doi.org/10.1016/j.epsl.2017.04.005 [^dangelo2012]: D'Angelo, G.; Marzari, F. (2012). "Outward migration of Jupiter and Saturn in evolved gaseous disks". *The Astrophysical Journal* 757: 50. https://doi.org/10.1088/0004-637X/757/1/50 [^chametla2020]: Chametla, R. O.; D'Angelo, G.; Reyes-Ruiz, M.; Sánchez-Salcedo, F. J. (2020). "Capture and migration of Jupiter and Saturn in mean motion resonance in a gaseous protoplanetary disc". *Monthly Notices of the Royal Astronomical Society* 492: 6007–6018. https://doi.org/10.1093/mnras/staa260 [^griveaud2023]: Griveaud, P.; Crida, A.; Lega, E. (2023). "Migration of pairs of giant planets in low-viscosity discs". *Astronomy & Astrophysics* 672: A190. https://doi.org/10.1051/0004-6361/202245208 [^pierens2014]: Pierens, A.; Raymond, S. N.; Nesvorný, D.; Morbidelli, A. (2014). "Outward migration of Jupiter and Saturn in 3:2 or 2:1 resonance in radiative disks: implications for the Grand Tack and Nice models". *The Astrophysical Journal Letters* 795: L11. https://doi.org/10.1088/2041-8205/795/1/L11 [^marzari2013]: Marzari, F.; D'Angelo, G. (2013). "Mass growth and evolution of giant planets on resonant orbits". *AAS/Division for Planetary Sciences Meeting* 45, abstract 113.04. Bibcode 2013DPS....4511304M. [^chambers2013]: Chambers, J. E. (2013). "Late-stage planetary accretion including hit-and-run collisions and fragmentation". *Icarus* 224: 43–56. https://doi.org/10.1016/j.icarus.2013.02.015 [^fischer2014]: Fischer, R. A.; Ciesla, F. J. (2014). "Dynamics of the terrestrial planets from a large number of N-body simulations". *Earth and Planetary Science Letters* 392: 28–38. https://doi.org/10.1016/j.epsl.2014.02.011 [^izidoro2015]: Izidoro, A.; Raymond, S. N.; Morbidelli, A.; Winter, O. C. (2015). "Terrestrial planet formation constrained by Mars and the structure of the asteroid belt". *Monthly Notices of the Royal Astronomical Society* 453: 3620–3635. https://doi.org/10.1093/mnras/stv1835 [^drazkowska2016]: Drążkowska, J.; Alibert, Y.; Moore, B. (2016). "Close-in planetesimal formation by pile-up of drifting pebbles". *Astronomy & Astrophysics* 594: A105. https://doi.org/10.1051/0004-6361/201628983 [^clement2018]: Clement, M. S.; Kaib, N. A.; Raymond, S. N.; Walsh, K. J. (2018). "Mars' growth stunted by an early giant planet instability". *Icarus* 311: 340–356. https://doi.org/10.1016/j.icarus.2018.04.008 [^levison2015]: Levison, H. F.; Kretke, K. A.; Walsh, K. J.; Bottke, W. F. (2015). "Growing the terrestrial planets from the gradual accumulation of submeter-sized objects". *Proceedings of the National Academy of Sciences* 112: 14180–14185. https://doi.org/10.1073/pnas.1513364112 [^broz2021]: Brož, M.; Chrenko, O.; Nesvorný, D.; Dauphas, N. (2021). "Early terrestrial planet formation by torque-driven convergent migration of planetary embryos". *Nature Astronomy* 5: 898–902. https://doi.org/10.1038/s41550-021-01383-3 [^bromley2017]: Bromley, B. C.; Kenyon, S. J. (2017). "Terrestrial planet formation: dynamical shake-up and the low mass of Mars". *The Astronomical Journal* 153: 216. https://doi.org/10.3847/1538-3881/aa6aaa [^raymond2017water]: Raymond, S. N.; Izidoro, A. (2017). "Origin of water in the inner Solar System: planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion". *Icarus* 297: 134–148. https://doi.org/10.1016/j.icarus.2017.06.030 [^raymond2017empty]: Raymond, S. N.; Izidoro, A. (2017). "The empty primordial asteroid belt". *Science Advances* 3: e1701138. https://doi.org/10.1126/sciadv.1701138 [^izidoro2016]: Izidoro, A.; Raymond, S. N.; Pierens, A.; et al. (2016). "The asteroid belt as a relic from a chaotic early Solar System". *The Astrophysical Journal* 833: 40. https://doi.org/10.3847/1538-4357/833/1/40 [^deienno2018]: Deienno, R.; Izidoro, A.; Morbidelli, A.; et al. (2018). "Excitation of a primordial cold asteroid belt as an outcome of planetary instability". *The Astrophysical Journal* 864: 50. https://doi.org/10.3847/1538-4357/aad55d [^zheng2017]: Zheng, X.; Lin, D. N. C.; Kouwenhoven, M. B. N. (2017). "Planetesimal clearing and size-dependent asteroid retention by secular resonance sweeping during the depletion of the solar nebula". *The Astrophysical Journal* 836: 207. https://doi.org/10.3847/1538-4357/836/2/207 [^ogihara2015]: Ogihara, M.; Kobayashi, H.; Inutsuka, S.; Suzuki, T. K. (2015). "Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system's terrestrial planets". *Astronomy & Astrophysics* 579: A65. https://doi.org/10.1051/0004-6361/201525636 [^volk2015]: Volk, K.; Gladman, B. (2015). "Consolidating and crushing exoplanets: did it happen here?". *The Astrophysical Journal Letters* 806: L26. https://doi.org/10.1088/2041-8205/806/2/L26 [^morbidelli2016]: Morbidelli, A.; Bitsch, B.; Crida, A.; et al. (2016). "Fossilized condensation lines in the Solar System protoplanetary disk". *Icarus* 267: 368–376. https://doi.org/10.1016/j.icarus.2015.11.027 [^clement2021]: Clement, M. S.; Chambers, J. E.; Jackson, A. P. (2021). "Dynamical avenues for Mercury's origin. I. The lone survivor of a primordial generation of short-period protoplanets". *The Astronomical Journal* 161: 240. https://doi.org/10.3847/1538-3881/abf09f ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Grand_tack_hypothesis) : [Wikitube](https://en.wikitube.io/wiki/Grand_tack_hypothesis) · pinned revision [1372525839](https://en.wikipedia.org/w/index.php?oldid=1372525839) · 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-036 · explorer state `?view=composition`.*