17. KOKUBO AND IDA
FIG. 4. Time evolution of the maximum mass (solid curve) and the mean
mass (dashed curve) of the system.
thanthisrangearenotstatisticallyvalidsinceeachmassbinoften
has only a few bodies. First, the distribution tends to relax to a
暴走的成長の様子
平均値
最大の天体
微惑星の暴走的成長
?→ 原始惑星が誕生する
20 KOKUBO AND IDA
FIG. 3. Snapshots of a planetesimal system on the a–e plane. The circles
represent planetesimals and their radii are proportional to the radii of planetesi-
mals. The system initially consists of 3000 equal-mass (1023 g) planetesimals.
FIG. 4. Time evolution of the maximum mass (solid curve) and the mean
mass (dashed curve) of the system.
thanthisrangearenotstatisticallyvalidsinceeachmassbinoften
has only a few bodies. First, the distribution tends to relax to a
decreasing function of mass through dynamical friction among
(energy equipartition of) bodies (t = 50,000, 100,000 years).
Second, the distributions tend to ?atten (t = 200,000 years). This
is because as a runaway body grows, the system is mainly heated
by the runaway body (Ida and Makino 1993). In this case, the
eccentricity and inclination of planetesimals are scaled by the
軌道長半径 [AU]
軌道離心率
質量[1023g]
時間
[Kokubo & Ida, 2000]
18. FORMATION OF PROTOPLANETS FROM PLANETESIMALS 23
FIG. 7. Snapshots of a planetesimal system on the a–e plane. The cir- FIG. 8. The number of bodies in linear mass bins is plotted for t = 100,000,
寡占的成長の様子軌道離心率
各場所で微惑星が暴走的成長
?→ 等サイズの原始惑星が並ぶ
寡占的成長とよぶ
=
各軌道での原始惑星
質量 [kg] 形成時間 [yr]
地球軌道 1×1024 7×105
木星軌道 3×1025 4×107
天王星軌道 8×1025 2×109
軌道長半径 [AU]
21. ジャイアントインパクト
軌道長半径 [AU]
軌道離心率
planets is hnM i ’ 2:0 ? 0:6, which means that the typical result-
ing system consists of two Earth-sized planets and a smaller
planet. In this model, we obtain hnai ’ 1:8 ? 0:7. In other words,
one or two planets tend to form outside the initial distribution of
protoplanets. In most runs, these planets are smaller scattered
planets. Thus we obtain a high ef?ciency of h fai ? 0:79 ? 0:15.
The accretion timescale is hTacci ? 1:05 ? 0:58? ? ; 108
yr. These
results are consistent with Agnor et al. (1999), whose initial con-
Fig. 2.—Snapshots of the system on the a-e (left) and a-i (right) planes at t ? 0, 1
are proportional to the physical sizes of the planets.
KOKUBO, KOMIN1134
長い時間をかけて原始惑星同士の軌道が乱れる
?→ 互いに衝突?合体してより大きな天体に成長
[Kokubo & Ida, 2006]
25. 巨大ガス惑星の形成の様子
MACHIDA ET AL.1226
1.—Time sequence for model M04. The density (color scale) and velocity distributions (arrows) on the cross section in the ?z ? 0 plane are plotted. The bottom
? 3) are 4 times the spatial magni?cation of the top panels (l ? 1). Three levels of grids are shown in each top (l ? 1, 2, and 3) and bottom (l ? 3, 4, and 5) panel.
l of the outermost grid is denoted in the top left corner of each panel. The elapsed time ?tp and the central density ?c on the midplane are denoted above each of the
ls. The velocity scale in units of the sound speed is denoted below each panel.周囲の円盤ガスが原始惑星の重力圏内に捕獲される