Exposing cohesion forces in asteroids using fast rotating bodies

by David Polishook

at Astrophysics and Cosmology Seminar

Wed, 02 Dec 2015, 11:15
Physics building (#54) room 207

Abstract

Asteroids are considered to be collections of rocks separated by voids with no tensile strength to hold their components When an asteroid is spinning up its gravity supposed to be the only force resisting the centrifugal acceleration before the body breaks apart This notion is argumented by the observation that asteroids larger than 300 m do not rotate faster than 2 2 hours per cycle Smaller asteroids lt 300 m that reach faster rotations are therefore strong monolithic bodies from which the larger asteroids are composed In recent years theoreticians argue that friction and electrical Van der Wals forces can maintain the weak asteroid body by increasing its cohesion value and this is the force that allows small asteroids to rotate fast and not their supposed monolithic nature However the clear spin barrier at 2 2 hours for asteroids larger than 300 m serves as an argument against the non zero cohesion model since it requires a correlation between size and spin rate We report an observation of a 2 km size asteroid 60716 2000 GD65 with a lightcurve indicating a rotation period of 1 9529 0 0002 hours This adds to a handful of asteroids recently observed by the Palomar Transient Factory PTF survey Chang et al 2014 2015 with diameters between 0 5 1 5 km and lightcurves indicating rotation periods of 1 2 1 9 hours We apply the non zero cohesion model Holsapple 2007 to these asteroids and find that the fast rotating asteroids must have internal cohesive strength of at least 25 to 250 Pa in order to prevent disruption against centrifugal acceleration Similar cohesion values have been found within weak lunar soils 100 Pa Among the population of small asteroids only 10 must have substantial internal cohesion of over 1000 Pa to prevent disruption however none of them are rotating fast enough to require a fully monolithic body i e cohesion gt 10 kPa

Created on 22-11-2015 by Bar Lev, Yevgeny (ybarlev)
Updaded on 22-11-2015 by Bar Lev, Yevgeny (ybarlev)