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Wed July 11, 2012
Dr. Ilaria Pascucci, University of Arizona – Rules of Planetary Placement
In today’s Academic Minute, Dr. Ilaria Pascucci of the University of Arizona explains the rules that govern the messy process of solar system formation.
Ilaria Pascucci is an assistant professor of planetary sciences at the University of Arizona where her current research is focused on various aspects of solar system formation. More specifically, she is examining the dispersal of pre-planetary material around young stars. Her work has been published in a number of peer-reviewed journals and she holds a Ph.D. from the Max Plank Institute for Astronomy in Heidelberg, Germany.
Dr. Ilaria Pascucci – Rules of Planetary Placement
Planets form in disks of dust and gas around young stars. It is generally assumed that these disks are eventually dispersed by accreting on to the central star. We have recently found evidence that photoevaporative winds, driven by high-energy radiation from the central star, also play a major role in disk dispersal. An important property of photoevaporation is that it preferentially removes material from a specific location in the disk: for sun-like stars this location is at a radius of about 1AU, approximately where the Earth orbits the Sun.
Our research explores how photoevaporation influences the final locations of giant planets. Newly-formed planets do not stay fixed in position in their parent protoplanetary disks, but instead "migrate" inwards due to their gravitational interaction with the disk gas. We use a numerical model to follow the evolution of the disk due to accretion and photoevaporation, and to track the migration of giant planets. We ran a large number of these models, using randomly-sampled initial conditions, to generate statistical distributions of planet properties. Our major new result is that the final distribution of planets does not vary smoothly with distance from the star, but instead shows clear "deserts" and "pile-ups" of planets at particular locations, generally around 1-2AU, where photoevaporation carves a gap in the disk.
Our simulations provide a plausible explanation for the pile-up of giant planets at about 1 AU recently detected in exoplanet surveys, and we make predictions for how similar features should vary when we observe both stars and planets of different masses. As we discover more exoplanets we will be able to test these predictions in detail, and learn more about the conditions under which planets form.