At the same time, Jupiter's strong gravity takes control of the planetesimals. The giant planet hurls some of the material into the inner solar system, but it flings a substantial amount outward. To move a planet as heavy as Jupiter from 5 to 0.5 AU from the sun, however, would require a population of planetesimals 20 times as massive as the planet. Such a mammoth population may not exist in any planetary system. In this model, migration ends as soon as the planetesimals inside a planet's orbit are cleared out.
Planets thus avoid a death sentence.
I n another theory, it's the interaction between giant planets in the outer part of a planetary system that might draw one of them close to the star. As described by Frederic A. Rasio of the Massachusetts Institute of Technology, a close encounter between two or more giant planets produces a slingshot effect. Lin says that the interaction between giant planets may be the best explanation for why some have an elliptical orbit. Any giant planet propelled inward by this mechanism travels in an elliptical orbit. On the other hand, the disk model would tend to keep the path of a closely orbiting planet almost perfectly circular.