The Spin-Barrier Ratio for S and C-Type Main Asteroids Belt

TL;DR

This study investigates whether the spin-barrier ratio differs between C and S-type main belt asteroids, finding a slight difference that may be due to varying cohesion strengths, though data limitations prevent definitive conclusions.

Contribution

It provides an analysis of the spin-barrier ratio for C and S-type asteroids, highlighting potential differences linked to cohesion strength and emphasizing the need for more data.

Findings

The observed spin-barrier ratio for 4-20 km asteroids is approximately 1.20.

In the 4-10 km range, the ratio is about 1.11.

Uncertainties are high due to limited data on asteroid taxonomic classes.

Abstract

Asteroids of size larger than 0.15 km generally do not have periods P smaller than about 2.2 hours, a limit known as cohesionless spin-barrier. This barrier can be explained by means of the cohesionless rubble-pile structure model. In this paper we will explore the possibility for the observed spin-barrier value to be different for C and S-type Main Asteroids Belt (MBAs). On the basis of the actual bulk density values, the expected ratio between the maximum rotation periods is $P_C/P_S \approx 1.4 \pm 0.3$. Using the data available in the asteroid LightCurve Data Base (LCDB) we have found that, as regards the mean spin-barrier values and for asteroids in the 4-20 km range, there is a little difference between the two asteroids population with a ratio $P_C/P_S \approx 1.20 \pm 0.04$. Uncertainties are still high, mainly because of the small number of MBAs with known taxonomic class in the considered range. In the 4-10 km range, instead, the ratio between the spin-barriers seems closer to 1 because $P_C/P_S \approx 1.11 \pm 0.05$. This behavior could be a direct consequence of a different cohesion strength for C and S-type asteroids of which the ratio can be estimated.