because of the density of the asteroids (0.8 g/cm³) is less than water and about one third that of rock, the team of researchers led by f. marchis suggest that the patroclus system, previously thought to be a pair of rocky asteroids, is more similar to a comet in make up. it is thought that many trojan asteroids are in fact small planetesimals captured in the lagrange point of jupiter-sun system during the farther migration of the giant planets, 3.9 billion years ago. this scenario was suggested by a. morbidelli and colleagues in a series of articles published in may 2005 in "nature" journal.