[MGI40-P04] 太陽系外縁天体の軌道進化への銀河系ポテンシャルの影響
キーワード：太陽系外縁天体、第９惑星、銀河系
Recently many distant Trans Neptunian Objects (TNOs) have been
discovered. The range of their semi-major axes is in 100 AU to near
1000 AU.
Owing to the increasing number of the distant TNOs, the statistical
properties of their orbits become clear. One of their characteristic
properties is reported by Batygin and Brown (2016, AJ, 151). They
reported a clustering of orbital elements of distant and eccentric
TNOs. They found that the directions of periherions of TNOs with large
semi-major axes and high eccentricities are clustering.
They argue that the clustering is explained by the 9th planet. But the
9th planet has not been discovered yet. There may be another reason
for the clustering.
The Solar System is in the Galaxy. The Galactic gravitational field
is rarely taken into account in the study of dynamical evolution of
the Solar System. One of the reason may be its estimated weakness.
It is weak if the Galaxy is regarded as a sphere. However the Galaxy
is not a sphere. It is composed of a disk and a bar or spiral arms.
If we consider such a structure, its gravitational field is not weak.
And it is not known how it affects the orbital evolution of TNOs.
In this study, we numerically integrated the evolution of TNO's orbits
in a galaxy model which mimics the potential field by the Galactic
disk. We found that the Galactic potential causes large variations in
orbital elements of TNOs. We also found that the direction of
perihelion tends to turn towards the Galactic Center.
Our result suggests that the clustering of distant TNOs's orbits is
caused by the Galactic Field.
It also suggests that the structure and dynamical evolution of the
Galaxy has affected the orbital and dynamical evolution of planets and
small objects in the Solar System and, therefore, the importance of the
study of evolution of the Solar System in the more realistic Galaxy
model.
discovered. The range of their semi-major axes is in 100 AU to near
1000 AU.
Owing to the increasing number of the distant TNOs, the statistical
properties of their orbits become clear. One of their characteristic
properties is reported by Batygin and Brown (2016, AJ, 151). They
reported a clustering of orbital elements of distant and eccentric
TNOs. They found that the directions of periherions of TNOs with large
semi-major axes and high eccentricities are clustering.
They argue that the clustering is explained by the 9th planet. But the
9th planet has not been discovered yet. There may be another reason
for the clustering.
The Solar System is in the Galaxy. The Galactic gravitational field
is rarely taken into account in the study of dynamical evolution of
the Solar System. One of the reason may be its estimated weakness.
It is weak if the Galaxy is regarded as a sphere. However the Galaxy
is not a sphere. It is composed of a disk and a bar or spiral arms.
If we consider such a structure, its gravitational field is not weak.
And it is not known how it affects the orbital evolution of TNOs.
In this study, we numerically integrated the evolution of TNO's orbits
in a galaxy model which mimics the potential field by the Galactic
disk. We found that the Galactic potential causes large variations in
orbital elements of TNOs. We also found that the direction of
perihelion tends to turn towards the Galactic Center.
Our result suggests that the clustering of distant TNOs's orbits is
caused by the Galactic Field.
It also suggests that the structure and dynamical evolution of the
Galaxy has affected the orbital and dynamical evolution of planets and
small objects in the Solar System and, therefore, the importance of the
study of evolution of the Solar System in the more realistic Galaxy
model.