The spin-barrier ratio for S and C-type main asteroids belt

Asteroids of size larger than 0.15 km generally do not have periods P smaller than about 2.2 h, 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 PC/PS≈1.4±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 PC/PS≈1.20±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 PC/PS≈1.11±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.