A water budget dichotomy of rocky protoplanets from 26Al-heating


In contrast to the water-poor planets of the inner Solar System, stochasticity during planetary formation1,2 and order-of-magnitude deviations in exoplanet volatile contents3 suggest that rocky worlds engulfed in thick volatile ice layers4,5 are the dominant family of terrestrial analogues6,7 among the extrasolar planet population. However, the distribution of compositionally Earth-like planets remains insufficiently constrained3, and it is not clear whether the Solar System is a statistical outlier or can be explained by more general planetary formation processes. Here we use numerical models of planet formation, evolution and interior structure to show that a planet’s bulk water fraction and radius are anti-correlated with initial 26Al levels in the planetesimal-based accretion framework. The heat generated by this short-lived radionuclide rapidly dehydrates planetesimals8 before their accretion onto larger protoplanets and yields a system-wide correlation9,10 of planetary bulk water abundances, which, for instance, can explain the lack of a clear orbital trend in the water budgets of the TRAPPIST-1 planets11. Qualitatively, our models suggest two main scenarios for the formation of planetary systems: high-26Al systems, like our Solar System, form small, water-depleted planets, whereas those devoid of 26Al predominantly form ocean worlds. For planets of similar mass, the mean planetary transit radii of the ocean planet population can be up to about 10% larger than for planets from the 26Al-rich formation scenario.

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Fig. 1: Dehydration of icy planetesimals from 26Al-heating and resulting influence on planet water abundance.
Fig. 2: Gradual desiccation of protoplanets as a function of 26Al0 for planets with \(f_{{\mathrm{H}}_{\mathrm{2}}{\mathrm{O}}} > 0\).
Fig. 3: Qualitative sketch of the effects of 26Al enrichment on planetary accretion.
Fig. 4: Shift in mean transit radii between planetary populations with varying 26Al enrichment.

Code and data availability

The data that support the plots within this paper, precompiled versions of the custom computer codes used, and other findings of this study are available from the corresponding author upon reasonable request.


  1. 1.

    Alibert, Y. & Benz, W. Formation and composition of planets around very low mass stars. Astron. Astrophys. 598, L5 (2017).

    ADS  Google Scholar 

  2. 2.

    Raymond, S. N. & Izidoro, A. Origin of water in the inner Solar System: planetesimals scattered inward during Jupiter and Saturn’s rapid gas accretion. Icarus 297, 134–148 (2017).

    ADS  Google Scholar 

  3. 3.

    Kaltenegger, L. How to characterize habitable worlds and signs of life. Annu. Rev. Astron. Astrophys. 55, 433–485 (2017).

    ADS  Google Scholar 

  4. 4.

    Kuchner, M. J. Volatile-rich Earth-mass planets in the habitable zone. Astrophys. J. Lett. 596, L105–L108 (2003).

    ADS  Google Scholar 

  5. 5.

    Léger, A. et al. A new family of planets? ‘Ocean-planets’. Icarus 169, 499–504 (2004).

    ADS  Google Scholar 

  6. 6.

    Tian, F. & Ida, S. Water contents of Earth-mass planets around M dwarfs. Nat. Geosci. 8, 177–180 (2015).

    ADS  Google Scholar 

  7. 7.

    Ramirez, R. M. & Levi, A. The ice cap zone: a unique habitable zone for ocean worlds. Mon. Not. R. Astron. Soc. 477, 4627–4640 (2018).

    ADS  Google Scholar 

  8. 8.

    Grimm, R. E. & McSween, H. Y. Heliocentric zoning of the asteroid belt by aluminum-26 heating. Science 259, 653–655 (1993).

    ADS  Google Scholar 

  9. 9.

    Millholland, S., Wang, S. & Laughlin, G. Kepler multi-planet systems exhibit unexpected intra-system uniformity in mass and radius. Astrophys. J. Lett. 849, L33 (2017).

    ADS  Google Scholar 

  10. 10.

    Weiss, L. M. et al. The California-Kepler survey. V. Peas in a pod: planets in a Kepler multi-planet system are similar in size and regularly spaced. Astron. J. 155, 48–60 (2018).

    ADS  Google Scholar 

  11. 11.

    Dorn, C., Mosegaard, K., Grimm, S. L. & Alibert, Y. Interior characterization in multiplanetary systems: TRAPPIST-1. Astrophys. J. 865, 20–37 (2018).

    ADS  Google Scholar 

  12. 12.

    Fu, R. R. & Elkins-Tanton, L. T. The fate of magmas in planetesimals and the retention of primitive chondritic crusts. Earth. Planet. Sci. Lett. 390, 128–137 (2014).

    ADS  Google Scholar 

  13. 13.

    Lichtenberg, T., Golabek, G. J., Gerya, T. V. & Meyer, M. R. The effects of short-lived radionuclides and porosity on the early thermo-mechanical evolution of planetesimals. Icarus 274, 350–365 (2016).

    ADS  Google Scholar 

  14. 14.

    Monteux, J., Golabek, G. J., Rubie, D. C., Tobie, G. & Young, E. D. Water and the interior structure of terrestrial planets and icy bodies. Space Sci. Rev. 214, 39–72 (2018).

    ADS  Google Scholar 

  15. 15.

    Benz, W., Ida, S., Alibert, Y., Lin, D. & Mordasini, C. in Protostars and Planets VI (eds. Beuther, H. et al.) 691–713 (Univ. Arizona Press, Tucson, 2014).

  16. 16.

    Ansdell, M. et al. ALMA survey of Lupus protoplanetary disks. I. Dust and gas masses. Astrophys. J. 828, 46–61 (2016).

    ADS  Google Scholar 

  17. 17.

    Johansen, A., Mac Low, M.-M., Lacerda, P. & Bizzarro, M. Growth of asteroids, planetary embryos, and Kuiper belt objects by chondrule accretion. Sci. Adv. 1, e1500109 (2015).

    ADS  Google Scholar 

  18. 18.

    Schiller, M., Bizzarro, M. & Fernandes, V. A. Isotopic evolution of the protoplanetary disk and the building blocks of Earth and the Moon. Nature 555, 507–510 (2018).

    ADS  Google Scholar 

  19. 19.

    Alibert, Y. et al. The formation of Jupiter by hybrid pebble-planetesimal accretion. Nat. Astron. 2, 2397–3366 (2018).

    Google Scholar 

  20. 20.

    Lichtenberg, T., Parker, R. J. & Meyer, M. R. Isotopic enrichment of forming planetary systems from supernova pollution. Mon. Not. R. Astron. Soc. 462, 3979–3992 (2016).

    ADS  Google Scholar 

  21. 21.

    Lugaro, M., Ott, U. & Kereszturi, Á. Radioactive nuclei from cosmochronology to habitability. Prog. Part. Nucl. Phys. 102, 1–47 (2018).

    ADS  Google Scholar 

  22. 22.

    Delbo, M., Walsh, K., Bolin, B., Avdellidou, C. & Morbidelli, A. Identification of a primordial asteroid family constrains the original planetesimal population. Science 357, 1026–1029 (2017).

    ADS  Google Scholar 

  23. 23.

    Kuffmeier, M., Frostholm Mogensen, T., Haugbølle, T., Bizzarro, M. & Nordlund, Å. Tracking the distribution of 26Al and 60Fe during the early phases of star and disk evolution. Astrophys. J. 826, 22–47 (2016).

    ADS  Google Scholar 

  24. 24.

    Noack, L., Snellen, I. & Rauer, H. Water in extrasolar planets and implications for habitability. Space Sci. Rev. 212, 877–898 (2017).

    ADS  Google Scholar 

  25. 25.

    Unterborn, C. T., Desch, S. J., Hinkel, N. R. & Lorenzo, A. Inward migration of the TRAPPIST-1 planets as inferred from their water-rich compositions. Nat. Astron. 2, 297–302 (2018).

    ADS  Google Scholar 

  26. 26.

    Alibert, Y. On the radius of habitable planets. Astron. Astrophys. 561, A41 (2014).

    ADS  Google Scholar 

  27. 27.

    Rauer, H. et al. The PLATO 2.0 mission. Exp. Astron. 38, 249–330 (2014).

    ADS  Google Scholar 

  28. 28.

    Marcus, R. A., Sasselov, D., Stewart, S. T. & Hernquist, L. Water/icy super-Earths: giant impacts and maximum water content. Astrophys. J. Lett. 719, L45–L49 (2010).

    ADS  Google Scholar 

  29. 29.

    Inamdar, N. K. & Schlichting, H. E. Stealing the gas: giant impacts and the large diversity in exoplanet densities. Astrophys. J. Lett. 817, L13 (2016).

    ADS  Google Scholar 

  30. 30.

    Grimm, S. L. et al. The nature of the TRAPPIST-1 exoplanets. Astron. Astrophys. 613, A68 (2018).

    Google Scholar 

  31. 31.

    de Wit, J. et al. Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1. Nat. Astron. 2, 214–219 (2018).

    ADS  Google Scholar 

  32. 32.

    Bourrier, V. et al. Temporal evolution of the high-energy irradiation and water content of TRAPPIST-1 exoplanets. Astron. J. 154, 121–138 (2017).

    ADS  Google Scholar 

  33. 33.

    Ciesla, F. J., Mulders, G. D., Pascucci, I. & Apai, D. Volatile delivery to planets from water-rich planetesimals around low mass stars. Astrophys. J. 804, 9–20 (2015).

    ADS  Google Scholar 

  34. 34.

    Ormel, C. W., Liu, B. & Schoonenberg, D. Formation of TRAPPIST-1 and other compact systems. Astron. Astrophys. 604, A1 (2017).

    ADS  Google Scholar 

  35. 35.

    Drażkowska, J. & Dullemond, C. P. Planetesimal formation during protoplanetary disk buildup. Astron. Astrophys. 614, A62 (2018).

    ADS  Google Scholar 

  36. 36.

    Lichtenberg, T. et al. Impact splash chondrule formation during planetesimal recycling. Icarus 302, 27–43 (2018).

    ADS  Google Scholar 

  37. 37.

    Ikoma, M., Elkins-Tanton, L., Hamano, K. & Suckale, J. Water partitioning in planetary embryos and protoplanets with magma oceans. Space Sci. Rev. 214, 76–104 (2018).

    ADS  Google Scholar 

  38. 38.

    Kite, E. S. & Ford, E. B. Habitability of exoplanet waterworlds. Astrophys. J. 864, 75–102 (2018).

    ADS  Google Scholar 

  39. 39.

    Gerya, T. V. & Yuen, D. A. Robust characteristics method for modelling multiphase visco-elasto-plastic thermo-mechanical problems. Phys. Earth Planet. Inter. 163, 83–105 (2007).

    ADS  Google Scholar 

  40. 40.

    Golabek, G. J., Bourdon, B. & Gerya, T. V. Numerical models of the thermomechanical evolution of planetesimals: application to the acapulcoite–lodranite parent body. Meteorit. Planet. Sci. 49, 1083–1099 (2014).

    ADS  Google Scholar 

  41. 41.

    Crameri, F. et al. A comparison of numerical surface topography calculations in geodynamic modelling: an evaluation of the ‘sticky air’ method. Geophys. J. Int. 189, 38–54 (2012).

    ADS  Google Scholar 

  42. 42.

    Lodders, K. Solar System abundances and condensation temperatures of the elements. Astrophys. J. 591, 1220–1247 (2003).

    ADS  Google Scholar 

  43. 43.

    Castillo-Rogez, J. et al. 26Al decay: heat production and a revised age for Iapetus. Icarus 204, 658–662 (2009).

    ADS  Google Scholar 

  44. 44.

    Nicholson, R. B. & Parker, R. J. Supernova enrichment of planetary systems in lowmass star clusters. Mon. Not. R. Astron. Soc. 464, 4318–4324 (2017).

    ADS  Google Scholar 

  45. 45.

    Costa, A., Caricchi, L. & Bagdassarov, N. A model for the rheology of particle-bearing suspensions and partially molten rocks. Geochem. Geophys. Geosys. 10, Q03010 (2009).

    ADS  Google Scholar 

  46. 46.

    Siggia, E. D. High Rayleigh number convection. Annu. Rev. Fluid. Mech. 26, 137–168 (1994).

    ADS  MathSciNet  MATH  Google Scholar 

  47. 47.

    O’Brien, D. P., Izidoro, A., Jacobson, S. A., Raymond, S. N. & Rubie, D. C. The delivery of water during terrestrial planet formation. Space Sci. Rev. 214, 47–71 (2018).

    ADS  Google Scholar 

  48. 48.

    Castillo-Rogez, J. & Young, E. D. in Planetesimals: Early Differentiation and Consequences for Planets (eds Elkins-Tanton, L. T. & Weiss, B. P.) 92–114 (Cambridge Univ. Press, Cambridge, 2017).

  49. 49.

    Fu, R. R., Young, E. D., Greenwood, R. C. & Elkins-Tanton, L. T. in Planetesimals: Early Differentiation and Consequences for Planets (eds Elkins-Tanton, L. T. & Weiss, B. P.) 115–135 (Cambridge Univ. Press, Cambridge, 2017).

  50. 50.

    Machida, R. & Abe, Y. Terrestrial planet formation through accretion of sublimating icy planetesimals in a cold nebula. Astrophys. J. 716, 1252–1262 (2010).

    ADS  Google Scholar 

  51. 51.

    Larsen, K. K. et al. Evidence for magnesium isotope heterogeneity in the solar protoplanetary disk. Astrophys. J. Lett. 735, L37 (2011).

    ADS  Google Scholar 

  52. 52.

    Schiller, M., Connelly, J. N., Glad, A. C., Mikouchi, T. & Bizzarro, M. Early accretion of protoplanets inferred from a reduced inner Solar System 26Al inventory. Earth. Planet. Sci. Lett. 420, 45–54 (2015).

    ADS  Google Scholar 

  53. 53.

    Alibert, Y., Mordasini, C., Benz, W. & Winisdoerffer, C. Models of giant planet formation with migration and disc evolution. Astron. Astrophys. 434, 343–353 (2005).

    ADS  Google Scholar 

  54. 54.

    Mordasini, C., Alibert, Y. & Benz, W. Extrasolar planet population synthesis. I. Method, formation tracks, and mass–distance distribution. Astron. Astrophys. 501, 1139–1160 (2009).

    ADS  Google Scholar 

  55. 55.

    Mordasini, C., Alibert, Y., Benz, W. & Naef, D. Extrasolar planet population synthesis. II. Statistical comparison with observations. Astron. Astrophys. 501, 1161–1184 (2009).

    ADS  Google Scholar 

  56. 56.

    Mordasini, C., Mollière, P., Dittkrist, K.-M., Jin, S. & Alibert, Y. Global models of planet formation and evolution. Int. J. Astrobiol. 14, 201–232 (2015).

    Google Scholar 

  57. 57.

    Shakura, N. I. & Sunyaev, R. A. Black holes in binary systems. Observational appearance. Astron. Astrophys. 24, 337–355 (1973).

    ADS  Google Scholar 

  58. 58.

    Clarke, C. J., Gendrin, A. & Sotomayor, M. The dispersal of circumstellar discs: the role of the ultraviolet switch. Mon. Not. R. Astron. Soc. 328, 485–491 (2001).

    ADS  Google Scholar 

  59. 59.

    Matsuyama, I., Johnstone, D. & Hartmann, L. Viscous diffusion and photoevaporation of stellar disks. Astrophys. J. 582, 893–904 (2003).

    ADS  Google Scholar 

  60. 60.

    Sasselov, D. D. & Lecar, M. On the snow line in dusty protoplanetary disks. Astrophys. J. 528, 995–998 (2000).

    ADS  Google Scholar 

  61. 61.

    Weidenschilling, S. J. Aerodynamics of solid bodies in the solar nebula. Mon. Not. R. Astron. Soc. 180, 57–70 (1977).

    ADS  Google Scholar 

  62. 62.

    Dittkrist, K.-M., Mordasini, C., Klahr, H., Alibert, Y. & Henning, T. Impacts of planet migration models on planetary populations. Effects of saturation, cooling and stellar irradiation. Astron. Astrophys. 567, A121 (2014).

    Google Scholar 

  63. 63.

    Inaba, S., Tanaka, H., Nakazawa, K., Wetherill, G. W. & Kokubo, E. High-accuracy statistical simulation of planetary accretion: II. Comparison with N-body simulation. Icarus 149, 235–250 (2001).

    ADS  Google Scholar 

  64. 64.

    Inaba, S. & Ikoma, M. Enhanced collisional growth of a protoplanet that has an atmosphere. Astron. Astrophys. 410, 711–723 (2003).

    ADS  Google Scholar 

  65. 65.

    Fortier, A., Alibert, Y., Carron, F., Benz, W. & Dittkrist, K.-M. Planet formation models: the interplay with the planetesimal disc. Astron. Astrophys. 549, A44 (2013).

    ADS  Google Scholar 

  66. 66.

    Genda, H. & Abe, Y. Survival of a proto-atmosphere through the stage of giant impacts: the mechanical aspects. Icarus 164, 149–162 (2003).

    ADS  Google Scholar 

  67. 67.

    Schlichting, H. E., Sari, R. & Yalinewich, A. Atmospheric mass loss during planet formation: the importance of planetesimal impacts. Icarus 247, 81–94 (2015).

    ADS  Google Scholar 

  68. 68.

    Burger, C., Maindl, T. I. & Schäfer, C. M. Transfer, loss and physical processing of water in hit-and-run collisions of planetary embryos. Celest. Mech. Dyn. Astron. 130, 2–32 (2018).

    ADS  Google Scholar 

  69. 69.

    Bollard, J. et al. Early formation of planetary building blocks inferred from Pb isotopic ages of chondrules. Sci. Adv. 3, e1700407 (2017).

    ADS  Google Scholar 

  70. 70.

    Connelly, J. N. & Bizzarro, M. Lead isotope evidence for a young formation age of the Earth–Moon system. Earth. Planet. Sci. Lett. 452, 36–43 (2016).

    ADS  Google Scholar 

  71. 71.

    Pollack, J. B. et al. Formation of the giant planets by concurrent accretion of solids and gas. Icarus 124, 62–85 (1996).

    ADS  Google Scholar 

  72. 72.

    Alibert, Y. et al. Theoretical models of planetary system formation: mass vs. semi-major axis. Astron. Astrophys. 558, A109 (2013).

    Google Scholar 

  73. 73.

    Demircan, O. & Kahraman, G. Stellar mass–luminosity and mass–radius relations. Astrophys. Space. Sci. 181, 313–322 (1991).

    ADS  Google Scholar 

  74. 74.

    Alibert, Y., Mordasini, C. & Benz, W. Extrasolar planet population synthesis. III. Formation of planets around stars of different masses. Astron. Astrophys. 526, A63 (2011).

    ADS  Google Scholar 

  75. 75.

    Kennedy, G. M. & Kenyon, S. J. Stellar mass dependent disk dispersal. Astrophys. J. 695, 1210–1226 (2009).

    ADS  Google Scholar 

  76. 76.

    Mordasini, C. et al. Characterization of exoplanets from their formation. II. The planetary mass–radius relationship. Astron. Astrophys. 547, A112 (2012).

    Google Scholar 

  77. 77.

    Bodenheimer, P. & Pollack, J. B. Calculations of the accretion and evolution of giant planets: the effects of solid cores. Icarus 67, 391–408 (1986).

    ADS  Google Scholar 

  78. 78.

    Saumon, D., Chabrier, G. & van Horn, H. M. An equation of state for low-mass stars and giant planets. Astrophys. J. Suppl. 99, 713–741 (1995).

    ADS  Google Scholar 

  79. 79.

    Seager, S., Kuchner, M., Hier-Majumder, C. A. & Militzer, B. Mass–radius relationships for solid exoplanets. Astrophys. J. 669, 1279–1297 (2007).

    ADS  Google Scholar 

  80. 80.

    Guillot, T. On the radiative equilibrium of irradiated planetary atmospheres. Astron. Astrophys. 520, A27 (2010).

    ADS  MATH  Google Scholar 

  81. 81.

    Jin, S. et al. Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation. Astrophys. J. 795, 65–87 (2014).

    ADS  Google Scholar 

  82. 82.

    Jin, S. & Mordasini, C. Compositional imprints in density–distance–time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation. Astrophys. J. 853, 163–186 (2018).

    ADS  Google Scholar 

  83. 83.

    Adams, F. C., Fatuzzo, M. & Holden, L. Distributions of short-lived radioactive nuclei produced by young embedded star clusters. Astrophys. J. 789, 86–104 (2014).

    ADS  Google Scholar 

  84. 84.

    Gounelle, M. The abundance of 26Al-rich planetary systems in the Galaxy. Astron. Astrophys. 582, A26 (2015).

    ADS  Google Scholar 

  85. 85.

    Pfalzner, S. et al. The formation of the Solar System. Phys. Scr. 90, 068001 (2015).

    ADS  Google Scholar 

  86. 86.

    Parker, R. J., Lichtenberg, T. & Quanz, S. P. Was Planet 9 captured in the Sun’s natal star-forming region? Mon. Not. R. Astron. Soc. 472, L75–L79 (2017).

    ADS  Google Scholar 

  87. 87.

    Dwarkadas, V. V., Dauphas, N., Meyer, B., Boyajian, P. & Bojazi, M. Triggered star formation inside the shell of a Wolf–Rayet bubble as the origin of the Solar System. Astrophys. J. 851, 147–161 (2017).

    ADS  Google Scholar 

  88. 88.

    Kita, N. T. et al. 26Al–26Mg isotope systematics of the first solids in the early Solar System. Meteorit. Planet. Sci. 48, 1383–1400 (2013).

    ADS  Google Scholar 

  89. 89.

    Klahr, H. & Schreiber, A. Linking the origin of asteroids to planetesimal formation in the solar nebula. Proc. IAU 10 (S318), https://doi.org/10.1017/S1743921315010406 (2016).

  90. 90.

    Simon, J. B., Armitage, P. J., Youdin, A. N. & Li, R. Evidence for universality in the initial planetesimal mass function. Astrophys. J. Lett. 847, L12 (2017).

    ADS  Google Scholar 

  91. 91.

    Tsirvoulis, G., Morbidelli, A., Delbo, M. & Tsiganis, K. Reconstructing the size distribution of the primordial Main Belt. Icarus 304, 14–23 (2018).

    ADS  Google Scholar 

  92. 92.

    Meng, H. Y. A., Rieke, G. H., Su, K. Y. L. & Gáspár, A. The first 40 million years of circumstellar disk evolution: the signature of terrestrial planet formation. Astrophys. J. 836, 34–53 (2017).

    ADS  Google Scholar 

  93. 93.

    Kral, Q., Clarke, C. & Wyatt, M. in Handbook of Exoplanets (eds Deeg, H. J. & Belmonte, J. A.) https://doi.org/10.1007/978-3-319-30648-3_165-1 (Springer Living Reference, Springer, Cham, 2017).

  94. 94.

    Andrews, S. M., Wilner, D. J., Hughes, A. M., Qi, C. & Dullemond, C. P. Protoplanetary disk structures in Ophiuchus II. Extension to fainter sources. Astrophys. J. 723, 1241–1254 (2010).

    ADS  Google Scholar 

  95. 95.

    Hunter, J. D. Matplotlib: a 2D graphics environment. Comput. Sci. Eng. 9, 90–95 (2007).

    Google Scholar 

  96. 96.

    Jones, E. et al. SciPy: open source scientific tools for Python. http://www.scipy.org (2001).

  97. 97.

    Van Der Walt, S., Colbert, S. C. & Varoquaux, G. The NumPy array: a structure for efficient numerical computation. Preprint at https://arXiv/abs/1102.1523 (2011).

  98. 98.

    McKinney, W. Data structures for statistical computing in Python. In Proc. 9th Python in Science Conference (eds van der Walt, S. & Millman, J.) 51–56 (SciPy, 2010).

  99. 99.

    Waskom, M. et al. Seaborn v0.9.0. https://doi.org/10.5281/zenodo.1313201 (2018).

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The authors thank R. Parker for helping to initiate this project, E. Kite, T. Roger and C. Dorn for comments and discussions, and M. Bizzarro for comments that helped to improve the manuscript. T.L. was supported by ETH Zürich Research Grant ETH-17 13-1 and acknowledges partial financial support from the Swiss Society for Astrophysics and Astronomy through a MERAC travel grant. Y.A. acknowledges support from the Swiss National Science Foundation (SNSF). C.M. acknowledges support from the SNSF under grant BSSGI0_155816 ‘PlanetsInTime’. The numerical simulations in this work were partially performed on the EULER computing cluster of ETH Zürich. Parts of this work have been carried out within the framework of the National Center of Competence in Research PlanetS supported by the SNSF.

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T.L., G.J.G., M.R.M. and Y.A. initiated the project. T.L. and R.B. performed the theoretical calculations. T.V.G., Y.A. and C.M. led the development of the computer codes used. T.L. wrote the manuscript. All authors contributed to the discussion and the interpretation of the results.

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Correspondence to Tim Lichtenberg.

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Lichtenberg, T., Golabek, G.J., Burn, R. et al. A water budget dichotomy of rocky protoplanets from 26Al-heating. Nat Astron 3, 307–313 (2019). https://doi.org/10.1038/s41550-018-0688-5

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