# Evidence for universality in the initial planetesimal mass function

## TL;DR

This study uses high-resolution simulations to investigate whether the initial mass function of planetesimals depends on particle size, finding a consistent power-law distribution suggesting a universal formation process.

## Contribution

The paper provides evidence that the initial planetesimal mass function is nearly universal across different particle sizes, based on high-resolution simulation results.

## Key findings

- Mass functions follow a power-law with slope 1.5-1.7.
- No significant differences in mass functions across particle sizes.
- Small-scale turbulence structure appears universal.

## Abstract

Planetesimals may form from the gravitational collapse of dense particle clumps initiated by the streaming instability. We use simulations of aerodynamically coupled gas-particle mixtures to investigate whether the properties of planetesimals formed in this way depend upon the sizes of the particles that participate in the instability. Based on three high resolution simulations that span a range of dimensionless stopping time $6 \times 10^{-3} \leq \tau \leq 2$ no statistically significant differences in the initial planetesimal mass function are found. The mass functions are fit by a power-law, ${\rm d}N / {\rm d}M_p \propto M_p^{-p}$, with $p=1.5-1.7$ and errors of $\Delta p \approx 0.1$. Comparing the particle density fields prior to collapse, we find that the high wavenumber power spectra are similarly indistinguishable, though the large-scale geometry of structures induced via the streaming instability is significantly different between all three cases. We interpret the results as evidence for a near-universal slope to the mass function, arising from the small-scale structure of streaming-induced turbulence.