The Formation of Short-Period Resonant Planets:
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in postscript format:
How Did GL 876's Planets Form?
Questions? E-mail:
Geoff.Bryden@jpl.nasa.gov
.PS
1. The collapse of an interstellar cloud produces a central protostar surrounded by a protostellar disk. First planetesimals, then planets, form out of this disk.
2. Once planets grow to masses comparable to Jupiter, they open gaps in the disk. In this case, two planets are large enough to form gaps.
3. The waves excited by the protoplanets collide with each other in the ring between the planets. The resultant shocks cause the ring to spread out and disappear on a short timescale.
4. The outer and inner disk try to push the planets together, but they are initially held apart by the gas ring between them. Once the ring dissipates, the planets are forced together until they are locked into 2:1 resonance.
5. After gap formation, the planets tend to follow the bulk motion of the disk gas. As the gas accretes onto the central star, the planets also spiral inward. Their migration is stopped at small radii, perhaps by direct magnetic interaction with the central protostar.
6. Eventually the disk clears, leaving behind two short-period planets in 2:1 resonance.
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Evolution of disk surface density for a model with two protoplanets.
Both planets have mass equal to Jupiter while their fixed orbits are
separated by a factor of 2. The disk has H/r = 0.05.
The protoplanets open up gaps in their surrounding disk material after
~100 orbits, such that a ring of gas remains between
them (upper panel). The waves excited by the planets collide within
this ring, producing strong shocks and causing the ring to dissipate
(middle panel) and eventually disappear after ~1000 orbits
(lower panel).