Formation and Evolution of Planetary Systems
© ESO
Clément Baruteau Institut de Recherche en Astrophysique et Planétologie, CNRS/Université de Toulouse Master’s seminar, University of Toulouse, 24/11/2014 1
Objectives and outline Give a practical overview of the physical processes that determine the formation and evolution of planetary systems: → dynamics of protoplanetary discs → planets formation → planets orbital evolution
Discuss how models of planet formation and evolution can interpret observed properties of extrasolar planets
2
The CoRoT spacecraft
20 YEARS OF EXOPLANET SEARCH 3
20 years of exoplanet search 1800 extrasolar planets discovered by various techniques:
line of sight
Radial velocities
© ESO
4
20 years of exoplanet search 1800 extrasolar planets discovered by various techniques:
Transits
© Spitzer Space Telescope Website
5
20 years of exoplanet search 1800 extrasolar planets discovered by various techniques: The 4 planets known to date around star HR 8799: 4-7 MJup @ 68 AU 7-10 MJup @ 38 AU
7-10 MJup @ 14 AU
7-10 MJup @ 24 AU
Direct imaging reminder: 1AU = Sun-Earth mean distance = 150 millions km
Marois+ 10
6
20 years of exoplanet search 1800 extrasolar planets discovered by various techniques (radial velocities, transits, direct imaging…)
Around 1 in 4 exoplanets is part of a multi-planetary system
Amazing diversity of planet masses, orbital periods, eccentricities…
7
20 years of exoplanet search 0.5
0.5
Jupiter
0.4
0.4
102 0.3
0.3
10 0.2
0.2
Eccentricity
Planet mass [Earth mass]
103
Earth
1
0.1
0.1
10-1
07/2014
Mercury
1 data extracted from exoplanets.org
10
102 103 104 Orbital period [days]
105 0.0 0
1
2
3
4
0.0 8
20 years of exoplanet search 0.5
0.5
Jupiter
0.4
0.4
102 0.3
0.3
10 0.2
0.2
Eccentricity
Planet mass [Earth mass]
103
Earth
1
+: planets detected only by transit (mass is inferred from the massradius diagram of planets with both mass and radius determined)
10-1
0.1
0.1
07/2014
Mercury
1 data extracted from exoplanets.org
10
102 103 104 Orbital period [days]
105 0.0 0
1
2
3
4
0.0 9
20 years of exoplanet search Constraining the sky-projected obliquity of a planet by the Rossiter-MacLaughlin effect stellar spin axis planetary orbital axis
1
1
Adapted from Armitage 07
prograde orbit
10
20 years of exoplanet search Constraining the sky-projected obliquity of a planet by the Rossiter-MacLaughlin effect stellar spin axis planetary orbital axis
2
1
planetary orbital axis 1
Adapted from Armitage 07
prograde orbit
2
retrograde orbit
11
20 years of exoplanet search
retrograde
150
100
prograde
| Projected spin-orbit misalignment | [deg.]
Constraining the sky-projected obliquity of a planet by the Rossiter-MacLaughlin effect
50
0 4500
5000 5500 6000 6500 Effective temperature [Kelvin]
7000 12
Flock+ 13
DYNAMICS OF PROTOPLANETARY DISCS 13
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Discs have spirals
MWC 758 Grady+ 13
15
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Discs have spirals, vortex-like dust structures
HD 142527 Casassus+ 13 16
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Discs have spirals, vortex-like dust structures, or gaps!
HL Tau dust continuum with ALMA
ESO Press release 6 Nov 2014 17
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Discs have spirals, vortex-like dust structures, or gaps! Typical lifetime: 1-10 Myr
Mamajek 09
18
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Discs have spirals, vortex-like dust structures, or gaps! Typical lifetime: 1-10 Myr Accretion requires the in-falling gas to loose angular momentum (AM)
19
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Discs have spirals, vortex-like dust structures, or gaps! Typical lifetime: 1-10 Myr Accretion requires the in-falling gas to loose angular momentum (AM): 1. Redistribution of AM within the disc → requires turbulent transport, very often modeled by a turbulent viscosity
G. Lesur 20
Protoplanetary discs: fact sheet Geometrically thin (H≪R), rotationally-supported structures of gas and dust around young, pre-main sequence stars
Discs have spirals, vortex-like dust structures, or gaps! Typical lifetime: 1-10 Myr Accretion requires the in-falling gas to loose angular momentum (AM): 2. Extraction of AM from the disc by a magnetic wind → Magnetic field exerts a torque on the disc’s surface, which promotes accretion
G. Lesur
21
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
22
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
23
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
❗ ️torque
per unit mass
= dJ/dt with
p J = rv' ⌘ GM? r the specific angular momentum
24
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
25
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
→ self-sustained MHD turbulence with outward transport of angular momentum at a rate corresponding to
e.g., Fromang & Nelson 06
26
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
protoplanetary discs are actually poorly ionized! (ne / n < 10-13)
27
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
protoplanetary discs are actually poorly ionized! (ne / n < 10-13)
thermal collisions
0.1-1AU
28
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
protoplanetary discs are actually poorly ionized! (ne / n < 10-13) interstellar cosmic rays stellar X-Ray and far-UV photons
thermal collisions
0.1-1AU
~10AU
29
Angular momentum transport in protoplanetary discs: the Magneto-Rotational Instability (MRI) A disc dynamically coupled to a weak B field initiates the linear MRI if dΩ2 / dR < 0 Balbus & Hawley 91, Balbus 03
protoplanetary discs are actually poorly ionized! (ne / n < 10-13)
dead zone (“MRI quenched by Ohmic diffusion”)
0.1-1AU
~10AU
→ Ohmic diffusion (electrons-neutrals collisions) makes a large fraction of the bulk disc magnetically inactive Gammie 96 → Layered accretion 30
Comet “Tchouri” seen by Rosetta
© ESA
SCENARIOS OF PLANET FORMATION 31
Stars and their planets form out of giant molecular clouds…
U A 0 1 l a r e sev 5
The Eagle (M16) nebula NASA, ESA, STScI, J. Hester and P. Scowen
32
…which collapse under their own gravity to form protoplanetary discs made of gas and µm-sized dusts
≲ 105 yr
33
How to build up planets from there? 10-6 m DUST
107 m PLANET
size
34
How to build up planets from there? 10-6 m DUST
10-2 m 1
107 m PLANET
size
1. growth through physical collisions between dust grains
numerical simulation of the sticking between two ~0.1 mm particles 35
How to build up planets from there? 10-6 m DUST
107 m
10-2 m 1
PLANET
size
1. growth through physical collisions between dust grains
Sticking of dust grains in a laboratory experiment Weidling+ 12
36
How to build up planets from there? 10-6 m DUST
107 m
10-2 m ✔
2
PLANET
size
2. growth by collisions beyond cm sizes isn’t easy: - bouncing
Weidling+ 12 37
How to build up planets from there? 10-6 m DUST
107 m
10-2 m ✔
2
PLANET
size
2. growth by collisions beyond cm sizes isn’t easy: - bouncing - fragmentation
Guettler+ 10 38
How to build up planets from there? 10-6 m DUST
107 m
10-2 m ✔
2
PLANET
size
2. growth by collisions beyond cm sizes isn’t easy: - bouncing - fragmentation but may work with unequal size particles via mass transfer (“lucky particles”) Guettler+ 10 39
How to build up planets from there?
DUST
107 m
10-2 m ✔
PLANET
2
2. growth by collisions beyond cm sizes isn’t easy: - bouncing - fragmentation but may work with unequal size particles via mass transfer (“lucky particles”)
size
growth
10-6 m
T. Birnstiel, after Windmark+ 12 40
How to build up planets from there? 10-6 m
107 m
10-2 m
DUST
2
✔
PLANET
size
2. growth by collisions beyond cm sizes isn’t easy: - bouncing - fragmentation - radial drift ✓
v',gas = vK 1 +
v',dust = vK
c2s 2 vK
d log P d log R
◆1/2 T. Birnstiel 41
How to build up planets from there? 10-6 m DUST
107 m
10-2 m ✔
2
PLANET
size
2. growth by collisions beyond cm sizes isn’t easy: - bouncing - fragmentation - radial drift Inward drift is fastest for ~cm-sized particles, which only take ~100 yr to drift from 1AU to the star! T. Birnstiel 42
How to build up planets from there? 10-6 m DUST
10-2 m ✔
103 m 2
PLANETESIMAL
107 m PLANET
disc’s perturbed pressure
2. growth may still occur if radial drift is severely slowed down: - pressure maximum, which may trigger the Rossby-wave instability ➤
size
Li H.+ 01 anticyclonic vortex
43
How to build up planets from there? 10-6 m DUST
10-2 m ✔
103 m 2
PLANETESIMAL
107 m PLANET
size
2. growth may still occur if radial drift is severely slowed down: - pressure maximum - dust feedback onto the gas, which may trigger the streaming instability ➤ Formation of dust filaments by the streaming instability
Johansen+ 14
44
How to build up planets from there? 10-6 m DUST
10-2 m ✔
107 m
103 m ?
PLANETESIMAL
3
PLANET
size
3. Growth of planetesimals to planets is thought to occur by direct collisions in three steps: - (i) runaway growth: only a few (larger) bodies grow very rapidly (≲105 yr)
45
How to build up planets from there? 10-6 m DUST
10-2 m ✔
107 m
103 m ?
PLANETESIMAL
3
PLANET
size
3. Growth of planetesimals to planets is thought to occur by direct collisions in three steps: - (i) runaway growth: only a few (larger) bodies grow very rapidly (≲105 yr) - (ii) oligarchic growth: only the biggest planetesimals keep on growing to form planet embryos, until they have cleared their “feeding zone”
46
How to build up planets from there? 10-6 m DUST
10-2 m ✔
107 m
103 m ?
PLANETESIMAL
3
PLANET
size
3. Growth of planetesimals to planets is thought to occur by direct collisions in three steps: - (i) runaway growth: only a few (larger) bodies grow very rapidly (≲105 yr) - (ii) oligarchic growth: only the biggest planetesimals keep on growing to form planet embryos, until they have cleared their “feeding zone” - (iii) merging of the embryos to form the final planets assembly. Time to form a terrestrial planet depends much on location; typically takes 1-100 Myr. 47
How to build up planets from there? 10-6 m DUST
10-2 m ✔
107 m
103 m ?
PLANETESIMAL
✔
PLANET
size
total
3. Planet cores ≳ 10 Earth masses can rapidly accrete a gas envelope and become giant planets
gas core
Pollack+ 96 48
Alternative: formation by Gravitational Instability (GI) Local criterion for a disc to be gravitationally unstable: Toomre 64, Papaloizou & Savonije 91
49
Alternative: formation by Gravitational Instability (GI) Local criterion for a disc to be gravitationally unstable: Toomre 64, Papaloizou & Savonije 91
Non-linear evolution depends on disc's cooling timescale 1) → the disc fragments and breaks up into bound clumps with typical mass ≳ MJup
Paardekooper+ 11 50
Alternative: formation by Gravitational Instability (GI) Local criterion for a disc to be gravitationally unstable: Toomre 64, Papaloizou & Savonije 91
Non-linear evolution depends on disc's cooling timescale 1) → the disc fragments and breaks up into bound clumps with typical mass ≳ MJup → clumps (precursors of giant planets) rapidly migrate inwards, in general
Baruteau+ 13 51
Alternative: formation by Gravitational Instability (GI) Local criterion for a disc to be gravitationally unstable: Toomre 64, Papaloizou & Savonije 91
Non-linear evolution depends on disc's cooling timescale 2)
→ the disc reaches a quasi steady gravito-turbulent state, with outward transport of angular momentum through waves
Forgan+ 11
52
PLANETS ORBITAL EVOLUTION 53
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) < Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
54
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
< Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0 w
ak e
planet
-0.5 co-orbital perturbations
ke
star
0.0
wa
y / rp
0.5
-1.0 -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
55
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
< Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0 w
ak e
star
0.0
planet
rp ke
-0.5
Wake = over-density → torque (Г) exerted by the disc on the planet: = dJp /dt p where Jp = Mp GM? rp is the angular momentum of the planet, assumed to have a circular orbit
wa
y / rp
0.5
-1.0
→ -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
drp /dt ⇠ /Mp 56
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
< Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0 w
y / rp
0.5
ak e
star
0.0
planet
Torque on planet by inner wake
⇠ r p ⇥ F' > 0 → moves planet further out
rp
-0.5
-1.0 -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
57
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
< Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0
planet
star
0.0
rp Torque on planet by outer wake
ke
-0.5
⇠ r p ⇥ F' < 0
wa
y / rp
0.5
→ moves planet further in!
-1.0 -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
58
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
< Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0 w
ak e
star
0.0
planet
rp ke
-0.5
wa
y / rp
0.5
-1.0 -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
The total wake torque on the planet is negative and drives planets inward migration
59
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
< Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0
y / rp
0.5
planet
star
0.0
co-orbital perturbations = overdensity and under-density → also exert a torque on the planet, called corotation torque
-0.5 co-orbital perturbations
-1.0 -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
60
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0
y / rp
0.5
planet
star
0.0
-0.5 co-orbital perturbations
-1.0 -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
61
Planet-protoplanetary disc interactions 1. Low-mass planets (~Earth-mass planets) -0.05
0.00
0.05
0.10
0.00
0.05
0.10
4
3
< Relative perturbation of the gas surface density of a protoplanetary disc where a 5 Earth-mass planet forms
2
1
0
-0.05
1.5 protoplanetary gas disc
1.0
y / rp
0.5
planet
star
0.0
co-orbital perturbations = overdensity and under-density → also exert a torque on the planet, called corotation torque
-0.5 co-orbital perturbations
The corotation torque on the planet is generally positive and drives planets outward migration
-1.0 -1.5 -1.5
-1.0
Baruteau+ 13
-0.5
0.0 x / rp
0.5
1.0
1.5
62
Planet-protoplanetary disc interactions
cs 2 ⌃r6 ⌦4 /
0 , with
0
=
✓
Mp M?
◆2
Total torque on planet
1. Low-mass planets (~Earth-mass planets)
Bitsch+ 13
Depending on the physical properties of protoplanetary discs (density and temperature profiles, viscosity, radiative properties) terrestrial planets migrate either inward or outward 63
Planet-protoplanetary disc interactions
cs 2 ⌃r6 ⌦4 /
0 , with
0
=
✓
Mp M?
◆2
Total torque on planet
1. Low-mass planets (~Earth-mass planets)
Bitsch+ 13
Timescale? when Γ = -Γ0, the (inward) migration timescale at 1 AU is ~3 x 105 yr for an Earth-mass planet, and ~2x104 yr for a Neptune-mass planet 64
Planet-protoplanetary disc interactions 2. High-mass planets (~Jupiter-mass planets) < Gas surface density (log scale) of a protoplanetary disc perturbed by a Jupiter-mass planet
65
Planet-protoplanetary disc interactions 2. High-mass planets (~Jupiter-mass planets) 4
3
2
1
0
-5.0
-4.5
-5.0
-4.0
-4.5
-4.0
-3.5
-3.0
-3.5
-3.0
Log (Surface density) at t = 100.0Torb
1.5
< Gas surface density (log scale) of a protoplanetary disc perturbed by a Jupiter-mass planet
1.0
A massive planet depletes its coorbital (horseshoe) region:
y / rp
0.5
→ corotation torque suppressed 0.0
→ wake torque weakened; still is main driver of migration
-0.5 -1.0 -1.5 -1.5
-1.0
-0.5
0.0 x / rp
0.5
1.0
1.5 66
Planet-protoplanetary disc interactions 2. High-mass planets (~Jupiter-mass planets) 4
3
2
1
0
-5.0
-4.5
-5.0
-4.0
-4.5
-4.0
-3.5
-3.0
-3.5
-3.0
Log (Surface density) at t = 100.0Torb
1.5
< Gas surface density (log scale) of a protoplanetary disc perturbed by a Jupiter-mass planet
1.0
A massive planet depletes its coorbital (horseshoe) region:
y / rp
0.5
→ corotation torque suppressed 0.0
→ wake torque weakened; still is main driver of migration
-0.5
Giant Jupiter-like planets thus migrate inward, on timescales > 104-5 yr.
-1.0 -1.5 -1.5
-1.0
-0.5
0.0 x / rp
0.5
1.0
1.5 67
Comparing models and observations OBSERVATIONS
THEORY (population syntheses) -
planet formation by core-accretion migration via disc-planet interactions no multi-planet interactions…
Dittkrist+ 14 68
Planet-protoplanetary disc interactions 3. Disc migration of several planets Convergent migration can lead to: capture into Mean-Motion Resonance (ratio of orbital periods is a rationale number). Planet-planet interactions increase eccentricities and inclinations, disc-planet interactions damp them
Baruteau & Papaloizou 13
69
Planet-protoplanetary disc interactions 3. Disc migration of several planets Convergent migration can lead to: capture into Mean-Motion Resonance close encounters resulting in planets scattering or collisions
Marzari+ 10
70
Planet-protoplanetary disc interactions 3. Disc migration of several planets Convergent migration can lead to: capture into Mean-Motion Resonance close encounters resulting in planets scattering or collisions
Planet-planet scattering is a natural source of: eccentric exoplanets hot Jupiters with high obliquities, depending on the efficiency of star-planet tidal interactions at shrinking and circularizing the orbit
71
Summary
72
Summary
73
Any questions?
Suggested references Armitage 2001, Dynamics of Protoplanetary Disks, http://arxiv.org/abs/1011.1496 Armitage 2007, Lecture notes on the formation and early evolution of planetary systems, http://arxiv.org/abs/astro-ph/0701485 Baruteau et al. 2013, Planet-disc interactions and the early evolution of planetary systems, http://arxiv.org/abs/1312.4293 Johansen et al. 2014, The multifaceted planetesimal formation process, http:// arxiv.org/abs/1402.1344 Turner et al. 2014, Transport and Accretion in Planet-Forming Disks, http://arxiv.org/ abs/1401.7306 74
