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Why Hot Jupiters are Single
  Astronomy and astrophysics

Friday 31 October 2014
from 10:30 to 11:30
at FA31
Speaker : Alexander Mustill (Lund)
Abstract : The origin of 'Hot Jupiters' -- giant planets orbiting a few hundredths of an AU from their host star -- is currently not understood. They cannot form in situ, instead forming at several AU and then migrating closer to the star; the mechanism underlying this migration is debated. In one mechanism ('disc migration'), gravitational torques exerted by the protoplanetary disc cause the planet to migrate. In the second mechanism ('dynamical migration'), the planet's orbital eccentricity is excited by other giant planets or stellar companions in the system after the protoplanetary disc has dissipated, and when the planet's pericentre becomes sufficiently small the orbit is shrunk by tidal dissipation. I argue that we can discriminate between these mechanisms by exploiting an observational fact about planetary multiplicity: Hot Jupiters are not found in the same system as lower-mass 'Super-Earths', despite these smaller planets being common around other stars. I show results of N-body simulations demonstrating that the typical result of a dynamically-migrating giant planet interacting with a Super-Earth system is the destruction of the Super-Earths, leaving a single eccentric giant planet that can evolve to become a Hot Jupiter. The fact that Hot Jupiters have no close, low-mass companions therefore provides evidence in support of a dynamical mechanism for the migration of these planets.

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