FORMATION OF CLOSE-IN PLANETS IN AN EVOLVING DISC€¦ · FORMATION OF CLOSE-IN PLANETS IN AN...
Transcript of FORMATION OF CLOSE-IN PLANETS IN AN EVOLVING DISC€¦ · FORMATION OF CLOSE-IN PLANETS IN AN...
FORMATION OF CLOSE-IN PLANETS IN AN EVOLVING DISC WITH N-BODY SIMULATIONS
Masahiro Ogihara (National Astronomical Observatory of Japan)
Eiichiro Kokubo (NAOJ), Takeru Suzuki (Univ. Tokyo), Alessandro Morbidelli (OCA)
Acknowledgments:
seealsoOgiharaetal.(2018,A&A)
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Masahiro Ogihara (NAOJ) / 14
Barrier in planet formation: Type I migration
0.3 M⊕
�2
(Suzuki et al.)
1 M⊕
5 M⊕
r (au
) 1
0.1
10
t (Myr)0.1 1 10
Rapid migration may cause several problems
Masahiro Ogihara (NAOJ) / 14
Key questions in this talk
�3
Q1: Is type I migration really problematic in close-in super-Earth formation?
Q2: If so, how can we overcome the migration problem?
Masahiro Ogihara (NAOJ) / 14
Close-in super-Earths
�4
Close-in super-Earths ・2401 planets (confirmed)
Multiple close-in super-Earth systems (N≧2) ・432 systems ・1082 planets (confirmed)
Mas
s (Ea
rth M
ass)
as of Aug. 2017
Masahiro Ogihara (NAOJ) / 14
Formation of super-Earths in a power-law disc
0.1
1
10
100
0.01 0.1 1
Mas
s (M
Earth
)
Semimajor Axis (AU)
(b)
0.1
1
10
100
0.01 0.1 1
Mas
s (M
Earth
)
Semimajor Axis (AU)
(a)
10-3
10-2
10-1
103
104
105103 yr
10-3
10-2
10-1
103
104
105104 yr
10-3
10-2
10-1
103
104
105105 yr
10-3
10-2
10-1
103
104
105106 yr
10-3
10-2
10-1
0.1 1103
104
105
Semimajor Axis (AU)
107 yr
Ecce
ntric
ity
Gas Surface D
ensity (g cm-2)
0.05 0.3
10-3
10-2
10-1
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104
105103 yr
10-3
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105106 yr
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0.1 1103
104
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Semimajor Axis (AU)
107 yr
Ecce
ntric
ity
Gas Surface D
ensity (g cm-2)
0.05 0.3
tacc ⇠ 103✓
⌃d
150 g/cm3
◆�1 ⇣ a
0.3 au
⌘27/10✓
M
M�
◆1/3
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inner edge MMSN
10 simulations observation
short growth timescale ↓ rapid type I migration
Mtot = 50 M⊕
pileup at disc edge
�5
(Ogihara, Morbidelli, Guillot 2015)
tmig~104yr
Masahiro Ogihara (NAOJ) / 14
2:13:24:35:4
6:5
Formation of super-Earths in a power-law disc
・observation: not in MMRs (mean motion resonances)・simulation: compact systems in MMRs (←rapid inward migration)
�6
observation
results of 10 runs of simulations
0 5
10 15 20 25 30
Num
ber
Period ratio (Pout/Pin) of adjacent pair
1 102 3 5
Masahiro Ogihara (NAOJ) / 14
Key questions in this talk
�7
Q1: Is type I migration really problematic in close-in super-Earth formation?
Q2: If so, how can we overcome the migration problem?
Yes. Due to rapid inward migration, results of simulations are inconsistent with observed distributions (e.g., period ratio).
Disc model.
Masahiro Ogihara (NAOJ) / 14
Disc evolution including disc winds
@⌃
@t=
1
r
@
@r
⇢2
r⌦
@
@r(r2⌃↵c2s ) + r
2↵w
⌃p⇡H
c2s
��+ Cw
⌃p⇡H
cs
viscous accretion(turbulence-driven)
wind-driven accretion(magnetic braking)
wind mass loss
MHD simulation (by T. Suzuki; X. Bai)
viscousaccretion
wind-driven accretion
wind mass loss
disc profiles can be altered from MMSN (r < 1 au) ・flat surface density slope ・decrease in density
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0.01 0.1 1 10 100Gas s
urfa
ce d
ensit
y (g
cm-2
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Radial distance (au)
initial
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ensit
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cm-2
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urfa
ce d
ensit
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cm-2
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urfa
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urfa
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urfa
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ensit
y (g
cm-2
)
Radial distance (au)
initial1Myr
10MyrMMSN
type I migration would change
(Suzuki, Ogihara, Morbidelli et al. 2016)
�8
Masahiro Ogihara (NAOJ) / 14
Formation of super-Earths including disc winds
Planets do not undergo significant migration
(Ogihara, Kokubo, Suzuki, Morbidelli 2018)
�9
initial total mass: Mtot = 40 M⊕
Masahiro Ogihara (NAOJ) / 14
Formation of super-Earths including disc winds
FORMATION PROCESSES
MMR chaingas dissipation
late orbital instability
not in mean-motion resonances
・instability→giant impacts
・gas dissipation (~a few Myr)
・slow migration → formation of MMRs
�10
(Ogihara, Kokubo, Suzuki, Morbidelli 2018)
Masahiro Ogihara (NAOJ) / 14
Formation of super-Earths including disc winds
Mtot = 40 M⊕Mtot = 20 M⊕ Mtot = 80 M⊕
0 0.2 0.4 0.6 0.8
1
1 10
Cum
ulativ
e dis
tribu
tion
Period ratio
2:13:24:35:46:5
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2 3 5(10 simulations each)
0 0.2 0.4 0.6 0.8
1
1 10
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ulativ
e dis
tribu
tion
Period ratio
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1 10
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ulativ
e dis
tribu
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Period ratio
2:13:24:35:46:5
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2 3 5
�11
(Ogihara, Kokubo, Suzuki, Morbidelli 2018)
Observed distribution can be reproduced when the migration is slow
Masahiro Ogihara (NAOJ) / 14
Key questions in this talk
�12
Q1: Is type I migration really problematic in close-in super-Earth formation?
Q2: If so, how can we overcome the migration problem?
Yes. Due to rapid inward migration, results of simulations are inconsistent with observed distributions (e.g., period ratio).
Type I migration can be slowed down if the disc is depleted (→slope, Σg) in the close-in region
Masahiro Ogihara (NAOJ) / 14
Comment on different approach
�13
10−1
100
105 106 107
Sem
imaj
or a
xis
(au)
Time (yr)
/Users/ogihara/home/m000/run−Aug18/run459/fig
10−2
10−1
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102
103
105 106 107
Mco
re (M
Earth
)
Time (yr)
/Users/ogihara/home/m000/run−Aug18/run459/fig
101
102
103
104
105
0.01 0.1 1 10 100
Σ g (g
cm-2
)
r (au)
initial0.1Myr
1Myr
❏ Model・disc model (Bitsch et al. 2015)
・initial total solid: 1M⊕・pebble accretion
Slow migration is favored
・Slow migration (~Myr)・Planets reach SE-mass in the late phase・Planets are not in MMRs
(see also Lambrechts et al. 2019)
Masahiro Ogihara (NAOJ) / 14
Summary
❏ N-body simulations of formation of close-in super-Earths
❏ Rapid type I migration results in compact systems in MMRs
❏ If the gas density is depleted in the close-in region (e.g., Suzuki et al. 2016), type I migration can be slowed down
❏ Observed properties of close-in super-Earths can be reproduced (ie, not in MMRs)
0 0.2 0.4 0.6 0.8
1
1 10Cu
mula
tive
distri
butio
nPeriod ratio
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7:6
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)
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initial
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ensit
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initial1Myr
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urfa
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initial1Myr
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initial1Myr
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urfa
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initial1Myr
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0.01 0.1 1 10 100Gas s
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Radial distance (au)
initial1Myr
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urfa
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initial1Myr
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)
Radial distance (au)
initial1Myr
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0.01 0.1 1 10 100Gas s
urfa
ce d
ensit
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initial1Myr
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urfa
ce d
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Radial distance (au)
initial1Myr
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0.01 0.1 1 10 100Gas s
urfa
ce d
ensit
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cm-2
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Radial distance (au)
initial1Myr
10Myr
�14
seealsoOgiharaetal.(2018,A&A)