Building Planets

Planet (and satellite) formation occurs by collisions, which can be energetic enough to cause global melting. During collisions, iron is delivered to the core of the growing planet, which has observable chemical and isotopic effects. Some recent work is summarized in a recent review article.

Much of my work has involved combining modelling of planetary dynamics with calculations of the chemical consequences. This approach can tell us things like how fast Mars formed, and how the Moon and the Earth ended up with identical isotopic signatures.

Most accretion simulations assume that all collisions result in perfect mergers, whereas in fact some collisions can knock chunks off the target. One of my former graduate students, Tina Dwyer, looked at how collisional erosion can affect the bulk chemistry and isotopic makeup of the surviving planets.

Satellite formation works in a similar way to planet formation. At least for Jupiterís moons, collisional erosion during accretion is not very important. But what is very important, especially for small moons, is the so-called Late Heavy Bombardment which happened about 3.9 billion years ago. This resulted in a large flux of high-velocity impactors which would have blasted apart the small moons several times over.

Cartoon of how core formation evolves as a planet grows (taken from this article). The chemical effects of core formation depend on whether the incoming iron breaks up into cm-scale blobs or not.



Here is a list of my accretion-related papers:

  Magnesium isotope evidence that accretional vapour loss shapes planetary compositions, R.C. Hin, C.D. Coath, P.J. Carter, F. Nimmo, Y-J. Lai, P.A.E. Pogge von Strandmann, M. Willbold, Z. Leinhardt, M.J. Walter, T. Elliott, Nature , 549 511-515, 2017.

  Early differentiation and core formation: Processes and timescales F. Nimmo, T. Kleine AGU Geophysical Monograph v. 212, The Early Earth: Accretion and Differentiation , pp. 83-102, 2015 Preprint.

  Disruption and re-accretion of mid-sized moons during an outer Solar System Late Heavy Bombardment N. Movshovitz, F. Nimmo, D. Korycansky, E. Asphaug, J. Owen,Geophys. Res. Lett. 42 doi:10.1002/2014GL062133, 2015 Reprint SOM

  Bulk chemical and Hf-W isotopic consequences of incomplete accretion during planet formation, C.A. Dwyer, F. Nimmo, J.E. Chambers, Icarus 245, 145-152, 2015 Reprint

  Accretion and differentiation of the terrestrial planets with implications for the compositions of early-formed Solar System bodies and accretion of water D.C. Rubie, S.A. Jacobson, A. Morbidelli, D.P. O'Brien, E.D. Young, J. de Vries, F. Nimmo, H. Palme, D.J. Frost Icarus 248 89-108, 2015 Reprint

  The effect of imperfect accretion and radial mixing on ice:rock ratios in the Galilean satellites, C.A. Dwyer, F. Nimmo, M. Ogihara, S. Ida, Icarus 225, 390-402, 2013 Preprint

  Impact-driven ice loss in outer solar system satellites: Consequences for the Late Heavy Bombardment, F. Nimmo, D.G. Korycansky Icarus 219, 508-510, 2012 Reprint

  Heterogeneous accretion, composition and core-mantle differentiation of the Earth, D.C. Rubie, D.J. Frost, U. Mann, Y. Asahara, F. Nimmo, K. Tsuno, P. Kegler, A. Holzheid, H. Palme Earth Planet. Sci. Lett. 301 31-42, 2011 Reprint

  Tungsten isotopic evolution during late-stage accretion: constraints on Earth-Moon equilibration F. Nimmo, D.P. O'Brien, T. Kleine Earth Planet. Sci. Lett. 292 363-370, 2010 Reprint

  Hf-W chronometry and the accretion and early evolution of asteroids and terrestrial planets T. Kleine, M. Touboul, B. Bourdon, F. Nimmo, K. Mezger, H. Palme, Q.-Z. Yin, S.B. Jacobsen, A.N. Halliday Geochim. Cosmochim. Acta, 73 5150-5188, 2009 Reprint (PDF)

  How rapidly did Mars accrete? Uncertainties in the Hf-W timing of core formation, F. Nimmo and T. Kleine Icarus ,191, , 497-504, 2007.Preprint (PDF)

  Formation of the Earth's core D.C. Rubie, F. Nimmo and H.J. Melosh, Treatise on Geophysics vol. 9, pp. 51-90, (G. Schubert, ed.), 2007. Email me if you want a reprint.

  The Origin of the Core F. Nimmo, Encyclopedia of Geomagnetism and Paleomagnetism, D. Gubbins and E. Herrero-Bervera, eds., Springer, pp.89-91, 2007. Preprint (PDF)

  Isotopic outcomes of N-body accretion simulations: Constraints on equilibration processes during large impacts from Hf/W observations,F. Nimmo and C.B. Agnor, Earth Planet. Sci. Lett. , 243, 26-43, 2006. Reprint (PDF)

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Last Modified: 20th Nov 2017