Giant Planet Migration and Volatile Transport in the Early Solar System
Kevin Walsh, Southwest Research Institute
Planets move… This is the paradigm shift that has developed over the last 20 years and changed the way that planet formation is understood. In fact, nearly every stage of planetary formation, for nearly every size planet, is marked by mechanisms capable of moving solid material great distance across solar system.
When planets move around, they can leave enormous scars in the populations of asteroids and comets. While we can’t directly observe these populations in planetary systems around other stars, in our own Solar System the small bodies are valuable tracers of past dynamical evolution. In the outer Solar System the orbit of Pluto and its cohorts in the Kuiper Belt indicate past migration of Neptune and Uranus , while the Trojan asteroids at Jupiter and the Main Asteroid Belt suggest that Jupiter and Saturn also moved in one “late” dynamical event  (where “late” means hundreds of millions of years after the planets finished forming).
Meanwhile, in the inner Solar System, the meteorite collection on Earth has indicated that one class of asteroids are the likely source for most of the water on Earth. This population is predominately found in the outer reaches of the main Asteroid Belt--far from Earth. Therefore the delivery of the right amount of these water-rich asteroids to the Earth imposes strict constraints on the evolution of our Solar System, and points to “early” migration of the giant planets [3,4] (where “early” means only a few million years into Solar System history, while the Earth was still forming).
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