Abstract
Most asteroids with a diameter larger than sim 300 {mathrm{m}} are rubble piles, i.e., consisting of more than one solid object. All asteroids are rotating but almost all asteroids larger than sim 300 mathrm{m} rotate with a period longer than 2.3 {text{hours}}, which is the critical period where the centrifugal force equals the gravitational force. This indicates that there are nearly no adhesive interaction forces between the asteroid fragments. We show that this is due to the surface roughness of the asteroid particles which reduces the van der Waals interaction between the particles by a factor of 100 for micrometer sized particles and even more for larger particles. We show that surface roughness results in an interaction force which is independent of the size of the particles, in contrast to the linear size dependency expected for particles with smooth surfaces. Thus, two stone fragments of size 100 {mathrm{nm}} attract each other with the same non-gravitational force as two fragments of size 10 {mathrm{m}}.
Highlights
Asteroids are rocky, airless remnants left over from the early formation of our solar system about 4.6 billion years ago [1]
We will show below that because of surface roughness the adhesion force Fad for stiff rock particles does not depend on the size of the particles, contrary to what has been universally assumed in planetary sciences [12], and for van der Waals (VDW) interaction it is typically Fad ≈ 10−9 N
All surfaces of solids have surface roughness, and surfaces produced by fracture, as may be the case for asteroid particles due to collisions between asteroids or due to the impact of meteorites, have usually large roughness which exhibit self-affine fractal behavior
Summary
Airless remnants left over from the early formation of our solar system about 4.6 billion years ago [1]. Most of this ancient space debris can be found orbiting our Sun between Mars and Jupiter within the main asteroid belt (see Fig. 1). Most asteroids are irregularly shaped (see Fig. 2), but a few of the biggest are nearly spherical due to the influence of gravity (see Fig. 3). As they revolve around the Sun in (weakly) elliptical orbits, the asteroids rotate. The fundamental reason for this is surface roughness, which results in a
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