Yasuhiro Hasegawa, Ralph E. Pudritz
The large number of observed exoplanets ($\gtrsim $ 700) provides fundamental constraints on their origin that can be deduced by plotting the mass and orbital periods of planets in a single diagram. In this mass-period diagram, the most surprising features are 1) the (apparent) pile up of gas giants at a period of $\sim 500$ days ($\sim1$ AU) and 2) the so-called mass-period relation which indicates that planetary mass is an increasing function of orbital period. We show that inhomogeneities in protoplanetary disks play the central role in establishing such planetary system architectures. Disk inhomogeneities give rise to multiple (up to 3) trapping sites, known as planet traps, for rapid (type I) planetary migration of cores of gas giants. The viscous evolution of disks induces the movement of these traps. We compute the evolutionary tracks of accreting planetary cores as they move with their traps. We find that the formation of cores and subsequent slow gas accretion onto their envelopes take place mainly at the planet traps. The movement of planet traps slowly transports the planetary cores from large to small orbital radii. Towards the onset of the final runaway gas accretion onto the cores, protoplanets become massive enough to "drop-out" from the movement of the planet traps and now evolve by opening a gap in the disks and undergoing slow (type II) migration. Photoevaporation arising from far ultra violet (FUV) radiation from the central star totally disperses gas in the remaining disk at the end stage of disk evolution and terminates type II migration of gas giants and their radial movement in the mass-period diagram. Following these simultaneous growth and movement of protoplanets in evolving disks, we show how the mass-period relation eventually arises.
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http://arxiv.org/abs/1207.0690
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