Metals observed in the atmospheres of white dwarfs suggest that many have recently accreted planetary bodies. In some cases, the compositions observed suggest the accretion of material dominantly from the core (or the mantle) of a differentiated planetary body. Collisions between differentiated exoplanetesimalrrs produce such fragments. In this work, we take advantage of the large numbers of white dwarfs where at least one siderophile (core-loving) and one lithophile (rock-loving) species have been detected to assess how commonly exoplanetesimals differentiate. We utilize N-body simulations that track the fate of core and mantle material during the collisional evolution of planetary systems to show that most remnants of differentiated planetesimals retain core fractions similar to their parents, while some are extremely core rich or mantle rich. Comparison with the white dwarf data for calcium and iron indicates that the data are consistent with a model in which 66+−46 per cent have accreted the remnants of differentiated planetesimals, while 31+−55 per cent have Ca/Fe abundances altered by the effects of heating (although the former can be as high as 100 per cent, if heating is ignored). These conclusions assume pollution by a single body and that collisional evolution retains similar features across diverse planetary systems. These results imply that both collisions and differentiation are key processes in exoplanetary systems. We highlight the need for a larger sample of polluted white dwarfs with precisely determined metal abundances to better understand the process of differentiation in exoplanetary systems.
Bibliographical noteFunding Information:
AB acknowledges funding from a Royal Society Dorothy Hodgkin Fellowship. JHDH acknowledges an STFC studentship. BTG was supported by the UK STFC grant ST/P000495. PJC acknowledges support from UC Office of the President grant LFR-17-449059. The research leading to these results has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation programme no. 677706 (WD3D). AB acknowledges funding from a Royal Society Dorothy Hodgkin Fellowship (DH150130).
© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
- Circumstellar matter
- Planetary systems
- Planets and satellites: general
- White dwarfs