A possible long-lived asteroid population at the equilateral Lagrangian points of Saturn

Abstract

The Lagrangian equilateral points of a planetary orbit are points of equilibrium that trail at 60°, ahead (L4) or behind (L5), the trajectory of a planet. Jupiter is the only major planet in our Solar system harbouring a known population of asteroids at those locations. Here we report the existence of orbits close to the Lagrangian points of Saturn, stable at time-scales comparable to the age of the Solar system. By scaling with respect to the Trojan population we have estimated the number of objects that would populate the regions, which gives a significant figure. Moreover, mutual physical collisions over the age of the Solar system would be very rare, so the evaporation rate of this swarm arising from mutual interactions would be very low. A population of asteroids not self-collisionally evolved after their formation stage would be the first to be observed in our planetary system. Our present estimations are based on the assumption that the capture efficiency at Saturn's equilateral points is comparable with the one corresponding to Jupiter, thus our figures may be taken as upper limits. In any case, observational constraints on their number would provide fundamental clues to our understanding of the history of the outer Solar system. If they existed, the surface properties and size distribution of those objects would represent unusually valuable fossil records of our early planetary system.