Planetary Giant Impacts by Jacob Kegerreis

Author:Jacob Kegerreis
Language: eng
Format: epub
ISBN: 9783030499587
Publisher: Springer International Publishing

3.7 Conclusions

In the second half of this chapter, we revisited the study of the giant impact onto the young Uranus that may explain its spin and other strange features (Sect. 3.4), to demonstrate the tools presented in Chap. 2 and to test the numerical convergence of such simulations.

We find that even large-scale results such as the rotation rate are not converged with standard-resolution simulations of and particles. The overall behaviour is similar in all cases, but small variations in the debris that falls back after the initial impact have a significant effect on the post-impact planet and its rotation rate, which appears to be well-converged with and particles, but not fewer. Similar but mildly less certain convergence is seen for the masses of atmosphere and ice that are ejected from the system, while the low mass of rock placed into orbit has not converged at all by particles.

Increasing resolution is only one important challenge for developing more realistic simulations. We have here used a simple implementation of SPH with a focus on simply increasing the number of particles. Future studies must continue to test high resolutions with, for example, more sophisticated equations of state and improved SPH formulations with better treatment of issues such as material and density discontinuities.

We conclude that standard-resolution simulations with SPH particles can fail to produce reliable results even for large-scale properties of a planetary system. and particles appear to pass the threshold of resolving the major processes in a giant impact. However, different collisions and other specific simulation outputs will depend more or less strongly on the behaviour of smaller structures, with correspondingly different requirements for convergence. The highly non-linear nature of giant impacts and the combinations of short- and long-term, localised and distributed processes prevent simple predictions for how many particles will be sufficient for a given result to converge.

References

Ahrens T. J., 1993, Annu. Rev. Earth Planet. Sci., 21, 525. https://​doi.​org/​10.​1146/​annurev.​ea.​21.​050193.​002521

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