Formation of Super-Earths

  • Hilke E. Schlichting
Living reference work entry


Super-Earths are the most abundant planets known to date and are characterized by having sizes between that of Earth and Neptune, typical orbital periods of less than 100 days, and gaseous envelopes that are often massive enough to significantly contribute to the planet’s overall radius. Furthermore, super-Earths regularly appear in tightly packed multiple-planet systems, but resonant configurations in such systems are rare. This chapter summarizes current super-Earth formation theories. It starts from the formation of rocky cores and subsequent accretion of gaseous envelopes. We follow the thermal evolution of newly formed super-Earths and discuss their atmospheric mass loss due to disk dispersal, photoevaporation, core-cooling, and collisions. We conclude with a comparison of observations and theoretical predictions, highlighting that even super-Earths that appear as barren rocky cores today likely formed with primordial hydrogen and helium envelopes and discuss some paths forward for the future.


Planet formation Gas accretion Giant impacts Shocks Resonances Super-earth Mini-neptune Exoplanets Envelope evolution Atmospheric mass loss 


  1. Allard F, Hauschildt PH, Alexander DR, Tamanai A, Schweitzer A (2001) The limiting effects of dust in brown dwarf model atmospheres. ApJ 556:357–372ADSCrossRefGoogle Scholar
  2. Armitage PJ (2013) Astrophysics of planet formation. Cambridge University Press, Cambridge/New YorkGoogle Scholar
  3. Batalha NM, Rowe JF, Bryson ST et al (2013) Planetary candidates observed by Kepler. III. Analysis of the first 16 months of data. ApJS 204:24Google Scholar
  4. Batygin K (2015) Capture of planets into mean-motion resonances and the origins of extrasolar orbital architectures. MNRAS 451:2589–2609Google Scholar
  5. Borucki WJ, Koch D, Basri G et al (2010) Kepler planet-detection mission: introduction and first results. Science 327:977Google Scholar
  6. Carter JA, Agol E, Chaplin WJ et al (2012) Kepler-36: a pair of planets with neighboring orbits and dissimilar densities. Science 337:556Google Scholar
  7. Chen H, Rogers LA (2016) Evolutionary analysis of gaseous sub-Neptune-mass planets with MESA. ApJ 831:180ADSCrossRefGoogle Scholar
  8. D’Angelo G, Bodenheimer P (2013) Three-dimensional radiation-hydrodynamics calculations of the envelopes of young planets embedded in protoplanetary disks. ApJ 778:77ADSCrossRefGoogle Scholar
  9. Dawson RI, Lee EJ, Chiang E (2016) Correlations between compositions and orbits established by the giant impact era of planet formation. ApJ 822:54ADSCrossRefGoogle Scholar
  10. Deck KM, Batygin K (2015) Migration of two massive planets into (and out of) first order mean motion resonances. ApJ 810:119ADSCrossRefGoogle Scholar
  11. Fabrycky DC, Lissauer JJ, Ragozzine D et al (2014) Architecture of Kepler’s multi-transiting systems. II. New investigations with twice as many candidates. ApJ 790:146ADSCrossRefGoogle Scholar
  12. Freedman RS, Marley MS, Lodders K (2008) Line and mean opacities for ultracool dwarfs and extrasolar planets. ApJS 174:504–513Google Scholar
  13. Fressin F, Torres G, Charbonneau D et al (2013) The false positive rate of Kepler and the occurrence of planets. ApJ 766:81ADSCrossRefGoogle Scholar
  14. Fulton BJ, Petigura EA, Howard AW et al (2017) The California-Kepler survey. III. A gap in the radius distribution of small planets. ArXiv e-printsADSCrossRefGoogle Scholar
  15. Fung J, Artymowicz P, Wu Y (2015) The 3D flow field around an embedded planet. ApJ 811:101ADSCrossRefGoogle Scholar
  16. Ginzburg S, Sari R (2017) Tidal heating of young super-Earth atmospheres. MNRAS 464:3937–3944ADSCrossRefGoogle Scholar
  17. Ginzburg S, Schlichting HE, Sari R (2016) Super-Earth atmospheres: self-consistent gas accretion and retention. ApJ 825:29ADSCrossRefGoogle Scholar
  18. Ginzburg S, Schlichting HE, Sari R (2017) Core-powered mass loss sculpts the radius distribution of small exoplanets. ArXiv e-printsGoogle Scholar
  19. Goldreich P, Schlichting HE (2014) Overstable librations can account for the paucity of mean motion resonances among exoplanet pairs. AJ 147:32ADSCrossRefGoogle Scholar
  20. Greenzweig Y, Lissauer JJ (1990) Accretion rates of protoplanets. Icarus 87:40–77ADSCrossRefGoogle Scholar
  21. Hansen BMS, Murray N (2012) Migration then assembly: formation of Neptune-mass planets inside 1 AU. ApJ 751:158ADSCrossRefGoogle Scholar
  22. Hayashi C (1981) Structure of the solar nebula, growth and decay of magnetic fields and effects of magnetic and turbulent viscosities on the nebula. Prog Theor Phys Suppl 70:35–53Google Scholar
  23. Howard AW, Marcy GW, Bryson ST et al (2012) Planet occurrence within 0.25 AU of solar-type stars from Kepler. ApJS 201:15Google Scholar
  24. Hwang J, Chatterjee S, Lombardi J Jr, Steffen J, Rasio F (2017) Hydrodynamics of collisions between sub-Neptunes. ArXiv e-printsGoogle Scholar
  25. Ikoma M, Hori Y (2012) In situ accretion of hydrogen-rich atmospheres on short-period super-Earths: implications for the Kepler-11 planets. ApJ 753:66ADSCrossRefGoogle Scholar
  26. Inamdar NK, Schlichting HE (2015) The formation of super-Earths and mini-Neptunes with giant impacts. MNRAS 448:1751–1760ADSCrossRefGoogle Scholar
  27. Inamdar NK, Schlichting HE (2016) Stealing the gas: giant impacts and the large diversity in exoplanet densities. ApJ 817:L13ADSCrossRefGoogle Scholar
  28. Izidoro A, Raymond SN, Morbidelli A, Hersant F, Pierens A (2015) Gas giant planets as dynamical barriers to inward-migrating super-Earths. ApJ 800:L22Google Scholar
  29. Izidoro A, Ogihara M, Raymond SN et al (2017) Breaking the chains: hot super-Earth systems from migration and disruption of compact resonant chains. ArXiv e-printsADSCrossRefGoogle Scholar
  30. Jin S, Mordasini C, Parmentier V et al (2014) Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation. ApJ 795:65ADSCrossRefGoogle Scholar
  31. Lee EJ, Chiang E (2015) To cool is to accrete: analytic scalings for nebular accretion of planetary atmospheres. ApJ 811:41Google Scholar
  32. Lee EJ, Chiang E (2016) Breeding super-Earths and birthing super-puffs in transitional disks. ApJ 817:90Google Scholar
  33. Lehmer OR, Catling DC (2017) Rocky worlds limited to 1.8 Earth radii by atmospheric escape during a stars extreme UV saturation. Astrophys J 845(2):130. Scholar
  34. Liu SF, Hori Y, Lin DNC, Asphaug E (2015) Giant impact: an efficient mechanism for the devolatilization of super-Earths. ApJ 812:164Google Scholar
  35. Lopez ED, Fortney JJ (2013) The role of core mass in controlling evaporation: the Kepler radius distribution and the Kepler-36 density dichotomy. ApJ 776:2ADSCrossRefGoogle Scholar
  36. Lopez ED, Fortney JJ (2014) Understanding the mass-radius relation for sub-Neptunes: radius as a proxy for composition. ApJ 792:1ADSCrossRefGoogle Scholar
  37. Lopez ED, Fortney JJ, Miller N (2012) How thermal evolution and mass-loss sculpt populations of super-Earths and sub-Neptunes: application to the Kepler-11 system and beyond. ApJ 761:59ADSCrossRefGoogle Scholar
  38. Marcy GW, Butler RP, Fischer D et al (2001) A pair of resonant planets orbiting GJ 876. ApJ 556:296–301ADSCrossRefGoogle Scholar
  39. Marcy GW, Isaacson H, Howard AW et al (2014) Masses, radii, and orbits of small Kepler planets: the transition from gaseous to rocky planets. ApJS 210:20Google Scholar
  40. Mills SM, Fabrycky DC, Migaszewski C et al (2016) A resonant chain of four transiting, sub-Neptune planets. Nature 533:509–512Google Scholar
  41. Najita JR, Kenyon SJ (2014) The mass budget of planet-forming discs: isolating the epoch of planetesimal formation. MNRAS 445:3315–3329Google Scholar
  42. Ormel CW, Kuiper R, Shi JM (2015a) Hydrodynamics of embedded planets’ first atmospheres – I. A centrifugal growth barrier for 2D flows. MNRAS 446:1026–1040ADSCrossRefGoogle Scholar
  43. Ormel CW, Shi JM, Kuiper R (2015b) Hydrodynamics of embedded planets’ first atmospheres – II. A rapid recycling of atmospheric gas. MNRAS 447:3512–3525ADSCrossRefGoogle Scholar
  44. Owen JE, Alvarez MA (2016) UV driven evaporation of close-in planets: energy-limited, recombination-limited, and photon-limited flows. ApJ 816:34Google Scholar
  45. Owen JE, Jackson AP (2012) Planetary evaporation by UV & X-ray radiation: basic hydrodynamics. MNRAS 425:2931–2947Google Scholar
  46. Owen JE, Wu Y (2013) Kepler planets: a tale of evaporation. ApJ 775:105ADSCrossRefGoogle Scholar
  47. Owen JE, Wu Y (2016) Atmospheres of low-mass planets: the “Boil-off”. ApJ 817:107Google Scholar
  48. Pan M, Schlichting HE (2017) Avoiding resonance capture in multi-planet extrasolar systems. ArXiv e-printsGoogle Scholar
  49. Powell D, Murray-Clay R, Schlichting HE (2017) Using ice and dust lines to constrain the surface densities of protoplanetary disks. ApJ 840:93ADSCrossRefGoogle Scholar
  50. Rafikov RR (2006) Atmospheres of protoplanetary cores: critical mass for nucleated instability. ApJ 648:666–682.ADSCrossRefGoogle Scholar
  51. Raymond SN, Barnes R, Mandell AM (2008) Observable consequences of planet formation models in systems with close-in terrestrial planets. MNRAS 384:663–674ADSCrossRefGoogle Scholar
  52. Rein H (2012) Period ratios in multiplanetary systems discovered by Kepler are consistent with planet migration. MNRAS 427:L21–L24ADSGoogle Scholar
  53. Rogers LA (2015) Most 1.6 Earth-radius planets are not rocky. ApJ 801:41ADSCrossRefGoogle Scholar
  54. Schlichting HE (2014) Formation of close in super-Earths and mini-Neptunes: required disk masses and their implications. ApJ 795:L15ADSCrossRefGoogle Scholar
  55. Seager S, Kuchner M, Hier-Majumder CA, Militzer B (2007) Mass-radius relationships for solid exoplanets. ApJ 669:1279–1297ADSCrossRefGoogle Scholar
  56. Steffen JH, Fabrycky DC, Agol E et al (2013) Transit timing observations from Kepler – VII. Confirmation of 27 planets in 13 multiplanet systems via transit timing variations and orbital stability. MNRAS 428:1077–1087ADSCrossRefGoogle Scholar
  57. Tu L, Johnstone CP, Güdel M, Lammer H (2015) The extreme ultraviolet and X-ray sun in time: high-energy evolutionary tracks of a solar-like star. A&A 577:L3ADSCrossRefGoogle Scholar
  58. van Boekel R, Henning T, Menu J et al (2017) Three radial gaps in the disk of TW Hydrae imaged with SPHERE. ApJ 837:132ADSCrossRefGoogle Scholar
  59. Weiss LM, Marcy GW (2014) The mass-radius relation for 65 exoplanets smaller than 4 Earth radii. ApJ 783:L6ADSCrossRefGoogle Scholar
  60. Weiss LM, Marcy GW, Petigura EA et al (2017) The California-Kepler survey V. Peas in a pod: planets in a Kepler multi-planet system are similar in size and regularly spaced. ArXiv e-printsGoogle Scholar
  61. Wolfgang A, Lopez E (2015) How rocky are they? The composition distribution of Kepler’s sub-Neptune planet candidates within 0.15 AU. ApJ 806:183ADSCrossRefGoogle Scholar
  62. Wu Y, Lithwick Y (2013) Density and eccentricity of Kepler planets. ApJ 772:74ADSCrossRefGoogle Scholar

Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  1. 1.University of CaliforniaLos AngelesUSA
  2. 2.Massachusetts Institute of TechnologyCambridgeUSA

Section editors and affiliations

  • Ralph Pudritz
    • 1
  1. 1.Origins InstituteMcMaster UniversityHamiltonCanada

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