The timing of formation of the first planetesimals determines the mode of planetary accretion and their geophysical and compositional evolution. Astronomical observations of circumstellar disks and Solar System geochronology provide evidence for planetesimal formation during molecular cloud collapse, much earlier than previously estimated. Here we present distinct observational evidence from white dwarf planetary systems for planetesimal formation occurring during the first few hundred thousand years after cloud collapse in exoplanetary systems. A substantial fraction of white dwarfs have accreted planetary material rich in iron core or mantle material. For the exo-asteroids accreted by white dwarfs to form iron cores, substantial heating is required. By simulating planetesimal evolution and collisional evolution, we show that the most likely heat source is short-lived radioactive nuclides such as 26Al (which has a half-life of ~0.7 Myr). Core-rich materials in the atmospheres of white dwarfs, therefore, provide independent evidence for rapid planetesimal formation, concurrent with star formation.
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The code used to create Figs. 1–4 and the collisional evolution code is available at https://github.com/abonsor/collcascade and models for Fig. 2 are available at https://github.com/timlichtenberg/2stage_scripts_data.
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A.B. acknowledges support from a Royal Society Dorothy Hodgkin Research Fellowship (grant number DH150130) and a Royal Society University Research Fellowship (grant number URF\R1\211421). T.L. was supported by a grant from the Simons Foundation (SCOL award number 611576). J.D. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement number 714769. A.M.B. acknowledges support from a Royal Society funded PhD studentship (grant number RGFEA180174). We acknowledge fruitful discussions with M. Brouwers, L. Rogers, E. Lynch, A. Curry, T. Birnstiel, M. Wyatt and R. J. Parker.
The authors declare no competing interests.
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Bonsor, A., Lichtenberg, T., Dra̧żkowska, J. et al. Rapid formation of exoplanetesimals revealed by white dwarfs. Nat Astron 7, 39–48 (2023). https://doi.org/10.1038/s41550-022-01815-8