The origin of high eccentricity planets: The dispersed planet formation regime for weakly magnetized disks

In the tandem planet formation regime, planets form at two distinct sites where solid particles are densely accumulated due to the on/off state of the magnetorotational instability (MRI). We found that tandem planet formation can reproduce the solid component distribution of the Solar System and tends to produce a smaller number of large planets through continuous pebble flow into the planet formation sites. In the present paper, we investigate the dependence of tandem planet formation on the vertical magnetic field of the protoplanetary disk. We calculated two cases of B z = 3.4 × 10 −3 G and B z = 3.4 × 10 −5 G at 100 AU as well as the canonical case of B z = 3.4 × 10 −4 G. We found that tandem planet formation holds up well in the case of the strong magnetic field ( B z = 3.4 × 10 −3 G). On the other hand, in the case of a weak magnetic field ( B z = 3.4 × 10 −5 G) at 100 AU, a new regime of planetary growth is realized: the planets grow independently at different places in the dispersed area of the MRI-suppressed region of r = 8−30 AU at a lower accretion rate of M ˙ 10 − 7.4 M ⊙ yr − 1 . We call this the “dispersed planet formation” regime. This may lead to a system with a larger number of smaller planets that gain high eccentricity through mutual collisions.