16. 暴走的成長の様子
KOKUBO AND IDA
質量 [1023g]
KOKUBO AND IDA
軌道離心率
20
最大の天体
平均値
FIG. 4. Time evolution of the maximum mass (solid curve) and the mean
mass (dashed curve) of the system.
than this range are not statistically valid since each mass bin often
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 flatten (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
時間 [年]
FIG. 4. Time evolution of the maximum mass (solid curve) and the mean
mass (dashed curve) of the system.
軌道長半径 [AU]
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-
微惑星の暴走的成長
→ are not statistically valid since each mass bin often
原始惑星が誕生する
than this range
has only a few bodies. First, the distribution tends to relax to a
17. 寡占的成長の様子
FORMATION OF PROTOPLANETS FROM PLANETESIMALS
23
=
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
軌道離心率
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
FIG. 7. Snapshots of a planetesimal system on the a–e plane. The cir-
7×105
木星軌道
軌道長半径 [AU]
1×1024
25
3×10
7
4×10
天王星軌道
25
8×10
9
2×10
FIG. 8. The number of bodies in linear mass bins is plotted for t = 100,000,
20. ジャイアントインパクトの様子
KOKUBO, KOMIN
軌道離心率
1134
軌道長半径 [AU]
Fig. 2.—Snapshots of the system on the a-e (left) and a-i (right) planes at t ¼ 0, 1
are proportional to the physical sizes of the planets.
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
planets is hnM i ’ 2:0 Æ 0:6, which means that the typical resulting system consists of two Earth-sized planets and a smaller
planet. In this model, we obtain hna i ’ 1:8 Æ 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 efficiency of h fa i ¼ 0:79 Æ 0:15.
The accretion timescale is hTacc i ¼ ð1:05 Æ 0:58Þ ; 108 yr. These
results are consistent with Agnor et al. (1999), whose initial con-
24. 1226
MACHIDA ET AL.
巨大ガス惑星の形成の様子
1.— Time sequence for model M04. The density (color scale) and velocity distributions (arrows) on the cross section in the z ¼ 0 plane are plotted. The bottom
˜
¼ 3) are 4 times the spatial magnification of the top panels (l ¼ 1). Three levels of grids are shown in each top (l ¼ 1, 2, and 3) and bottom (l ¼ 3, 4, and 5) panel.
˜
l of the outermost grid is denoted in the top left corner of each panel. The elapsed time ˜p and the central density c on the midplane are denoted above each of the
t
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