Spins of large asteroids: Hint on a primordial distribution of their spin rates

TL;DR

This study investigates the spin rate distribution of large asteroids and Kuiper Belt objects, revealing that their observed rapid spins are primarily primordial, shaped by formation processes rather than collisions.

Contribution

It demonstrates that collision effects produce a power law tail in spin distributions, but the observed fast spins are mainly due to primordial formation mechanisms.

Findings

Collision-induced spin distribution follows a Levy distribution.

Large asteroids' spins peak at 0.15-0.5 revolutions/day due to collisions.

Observed spins of large asteroids and KBOs are dominated by primordial factors.

Abstract

The Asteroid Belt and the Kuiper Belt are relics from the formation of our solar system. Understanding the size and spin distribution of the two belts is crucial for a deeper understanding of the formation of our solar system and the dynamical process that govern it. In this paper, we investigate the effect of collisions on the evolution of the spin distribution of asteroids and KBO's. We find that the power law nature of the impactors' size distribution leads to a L\'evy distribution of the spin rates. This results in a power law tail of the spin distribution, in stark contrast to the usually quoted Maxwellian distribution. We show that for bodies larger than 10 km, collisions alone lead to spin rates peaking at 0.15-0.5 revolutions per day. Comparing that to the observed spin rates of large asteroids ($R>50$ km), we find that the spins of large asteroids, peaking at $\sim1-2$ revolutions per day, are dominated by a primordial component that reflects the formation mechanism of the asteroids. Similarly, the Kuiper Belt has undergone virtually no collisional spin evolution, assuming current day density. Collisions contribute a spin rate of $\sim0.01$ revolutions per day, thus the observed fast spin rates of KBOs are also primordial in nature.