Researchers may have discovered the secret ingredient of planet growth, which causes some worlds to grow rapidly in disks of gas and dust around infant stars. The model could be of specific value in understanding the growth of the solar system's giant planets. Scientists have a fairly good understanding of how the rocky inner planets of the solar system, Mercury, Venus, Earth and Mars, formed and evolved. But the current model of collisions and gathering of asteroid-like bodies called "planetesimals" and the accretion of gas over millions of years leaves a lot to be explained when it comes to the formation of the gas giants Jupiter and Saturn and the ice giants Neptune and Uranus. All these giants seem to have formed too far out from the sun to grow so massive, with the growth of the outer ice giants being particularly puzzling. Jupiter is 15 times further away from the sun than our planet, and Neptune is 30 times farther away from our star than Earth.