6:15 PM - 7:30 PM
[PPS21-P06] The inclination evolutions of protoplanets through giant impacts
Keywords:planetary accretion, giant impact phase, inclination
There are 899 transiting planet candidates in 365 multiple-planet systems, and 333 systems are only composed by 818 ungiant candidates, whose radii are smaller than 6 Earth radius, and which are composed by Neptunes and super-Earth.
When multiple planets are detected by the transit method, the mutual inclinations can be estimated by the ratio of transit duration times.
Fabrycky et al. (2014) suggested that the typical mutual inclination between Kepler candidates in multiple-planet systems lies in 1.0 degree - 2.2 degree.
Inclinations of protoplanets are excited by the mutual scatterings between them.
It is expected that protoplanets can excite the inclinations up to the half values given by their escape velocities.
The excited inclination is estimated as iesc = 5.4 degree for a 10 Earth mass planet at 0.1 AU.
The small inclinations of observed ungiants suggest that if they are formed in-situ accretion, some inclination damping mechanism is working.
Since the eccentricities of the merged protoplanets are damped through giant impacts between protoplanets, as pointed out by our previous study, the inclinations is expected to be damped by the giant impacts.
On the other hand, for a Earth mass planet at 1 AU, iesc = 8.6 degree.
The resultant planets from N-body simulations in the giant impact stage normally have i = 3 degree without any damping forces (e.g., Kokubo et al. 2006).
Ths smaller inclinations of calculated planets also suggest that inclinations are damped through the giant impact.
We investigate inclination evolutions through the collisions in the giant impact stage by N-body simulations.
We find that the inclination of the merger body is smaller than the larger inclination of the colliding two protoplanets.
The inclination after a collision is expressed as the function of the mutual inclination and the angular momenta.
Our N-body simulations suggest that the inclinations of observed ungiant planets can be reproduced by the in-situ accretion of planets in the gas-free environment.