Simplify the following text for a Grade 8 native English-speaking person.
Original: It is suspected that many Trojan asteroids are in fact small planetesimals captured in the Lagrange point of Jupiter-Sun system during the outer migration of the giant planets , 3.9 billion years ago .
Simplified: 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 .