Planets are particular about orbits

Planets forming around stars tend to pile up at certain distances, creating some crowded orbits while other regions remain empty, US astronomers say. Some orbital zones around new stars tend to attract numbers of giant planets and computer simulations suggest the reason may be high-energy radiation streaming from the stars, they said. The radiation creates gaps in the protoplanetary disks of gas and dust swirling around young stars in a process called photo-evaporation, where ultraviolet light and other high-energy photons from the star heat the disk material. Supercomputer models reveal "that the final distribution of planets does not vary smoothly with distance from the star, but instead has clear 'deserts' -- deficits of planets -- and 'pileups' of planets at particular locations," study co-author Ilaria Pascucci at the University of Arizona told SPACE.com Giant planets migrate inward, dragged by protoplanetary material falling toward the star, but one they encounter a gap cleared by photo-evaporation they stop their inward movement, taking up a stable orbit around the star, she said. "The planets either stop right before or behind the gap, creating a pileup," Pascucci said. "The local concentration of planets leaves behind regions elsewhere in the disk that are devoid of any planets. This uneven distribution is exactly what we see in many newly discovered solar systems."