14. 多様な円盤から生まれる多様な惑星
円盤の質量の違い → ガス惑星の数と位置の違い
random velocity of planetesimals is pumped up as high as
the escape velocity of protoplanets. This high random veloc-
ity makes the accretion process slow and inefficient and thus
Tgrow longer. This accretion inefficiency is a severe problem
On the ot
in circular o
HD 192263
with Æ1e1
for in situ f
case. It is di
slingshot m
circular orb
the magneti
may be wea
disks may b
Terrestria
Jovian plan
planetary a
key process
systems.
We confir
holds in
Æsolid ¼ Æ1ð
¼ 1=2; 3=
tions. We d
systems dep
disk profile
growth time
a
Mdisk T Tgrow diskT Tcont disk
Fig. 13.—Schematic illustration of the diversity of planetary systems
against the initial disk mass for 2. The left large circles stand for central
stars. The double circles (cores with envelopes) are Jovian planets, and the
others are terrestrial and Uranian planets. [See the electronic edition of the
原始惑星系円盤の質量
軌道長半径 (中心星からの距離)
18. 巨大惑星の移動に伴う惑星系の変化
earing continues through scattering. After
00 million years the inner disk is composed
the collection of planetesimals at 0.06 AU, a
M] planet at 0.12 AU, the hot Jupiter at 0.21
U, and a 3 M] planet at 0.91 AU. Previous
sults have shown that these planets are likely
be stable for billion-year time scales (15).
Many bodies remain in the outer disk, and ac-
orbital time scales and high inclinations.
Two of the four simulations from Fig. 2
contain a 90.3 M] planet on a low-eccentricity
orbit in the habitable zone, where the temper-
ature is adequate for water to exist as liquid on
a planet_s surface (23). We adopt 0.3 M] as a
lower limit for habitability, including long-term
climate stabilization via plate tectonics (24).
three categories: (i) hot Earth analogs interior to
the giant planet; (ii) Bnormal[ terrestrial planets
between the giant planet and 2.5 AU; and (iii)
outer planets beyond 2.5 AU, whose accretion
has not completed by the end of the simulation.
Properties of simulated planets are segregated
(Table 1): hot Earths have very low eccentric-
ities and inclinations and high masses because
g. 1. Snapshots in time of the evolution of one simulation. Each panel
ots the orbital eccentricity versus semimajor axis for each surviving body.
he size of each body is proportional to its physical size (except for the
ant planet, shown in black). The vertical ‘‘error bars’’ represent the sine
of each body’s inclination on the y-axis scale. The color of each dot
corresponds to its water content (as per the color bar), and the dark inner
dot represents the relative size of its iron core. For scale, the Earth’s water
content is roughly 10j3 (28).
巨大惑星が落下する際に
周囲の原始惑星の軌道を
大きくかき乱す
they accrete on the migration time scale (105
years), so there is a large amount of damping
during their formation. These planets are remi-
niscent of the recently discovered, close-in 7.5 M]
planet around GJ 876 (25), whose formation is
also attributed to migrating resonances (26).
多様な惑星系形成
19. !#$%'(#))#%* +,-./0./# 1233456,7#%,+
外側内側 a
GM
a
GM
a
GM
a
GM
a
GM **
3
*
2
*
1
* %%%
重い円盤で３個以上の巨大ガス惑星
が円軌道で形成 t ~ 1'()
形成後に離心率増大*%軌道交差
ひとつの惑星が系外へ+%残った惑星
は安定な楕円軌道へ+ 内側の惑星の
aは初期の半分程度+%外側の惑星の
aは広く分布+%
,-./0%e
軌道不安定による惑星系の変化
惑星間の重力の影響が
積み重なって最終的に
互いの軌道が不安定化
異なる惑星系へ
↓
Eccentric Planet の起源？
