Time: a new dimension of constraints for planet …...2014/12/03 · Time: a new dimension of...
Transcript of Time: a new dimension of constraints for planet …...2014/12/03 · Time: a new dimension of...
Time: a new dimension of constraints for planet formation and evolution theory
Christoph Mordasini
S. Jin, P. Mollière Max Planck Institut for Astronomy, Heidelberg, Germany Y. Alibert & W. Benz University of Bern, Switzerland
PLATO meeting Taormina 3.12.2014
Adding the temporal dimension with PLATO
“Stellar masses and ages will be tightly constrained by the systematic use of asteroseismology . … Ages will be known to 10% for solar-like stars.”
For the first time with PLATO: population-wide and accurate planet evolution in time as a measurable quantity on the observational side
Raue
r et a
l. 20
13
On the theoretical side: temporal evolution: a fundamental and omnipresent concept
Radius evolution and formationRadius evolution in time depends on
New constraints to better understand planet formation
Implication for planet formation
Formation location, migration, opacity in the protoatmosphere, planetesimal / pebble accretion
• Bulk composition (H/He, silicates, Fe, ices)
Accretion history, planetesimal size• Energy transport in the interior (convection)
Enrichment, formation location• Atmosphere & opacity
Efficiency of H/He accretion• Atmospheric escape/evaporation
Migration mechanism (Kozai, disk migration)
• Bloating mechanisms
(Giant) planet formation mode, gas accretion shock structure
• initial thermodynamic state (how hot initially / entropy)
Mordasini 2013Composition Init. cond.
Temporal evolution: giant planetsFo
rtney
et a
l. 20
11 Atmospheric model
Guillot & Show
man 2002
Inflation
Leco
nte
& C
habr
ier 2
013
Energy transport
Temporal evolution low-mass planet
All these R(time) curves are not directly observationally constrained
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Rad
ius
[Ear
th r
adii]
Time since formation [Myr]
total radius w/ evap
core radius 1
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0 2 4 6 8 10 12
Rad
ius
[Ear
th r
adii]
Time since formation [Myr]
total radius w/o evap Envelope mass
Time since disk dissipation [Myr]
10-5
10-4
10-3
10-2
10-1
0 2 4 6 8 10 12E
nvel
ope
Mas
s [E
arth
mas
ses]
Time since formation [Myr]Time since disk dissipation [Myr]
Venus atmosphere mass
Mini-Neptune a=0.05 AU Mcore=4 MEarth Menv=0.1 MEarth
Linit=0.1 LJ Earth-like core (0.33 iron, 0.66 silicate) X-rays & EUV evaporation Solar-composition opacity
-fast decrease from ~2 REarth to R=Rcore when envelope totally lost
Temporal evolution of the a-M diagram
Mstar=1 Msun , isothermal type I migration rate x 0.1, cold accretion. 1 embryo/disk, no special inflation mechanisms.
a-M does not change much. (a>0.06 AU)
Close-in, low-mass loose the envelope.
Most of the action early on.
Black: Bare rocky coresJin et al. 2013
Output of core accr. population synthesis
Thermodynamic evolution (cooling & contraction) in time w. atmos. escape
Only thermodynamic evolutionNot dynamics
Mstar=1 Msun Isothermal Type I rate x 0.1. Cold accretion. 1 embryo/disk, no special inflation mechanisms.
Black: Bare rocky cores
Artifact of using Mmin=1 MEarth
Temporal evolution of the a-R diagram
-Contraction -Evaporation -Empty valley below 1-2 REarth
a-R does change!
Radius distribution as a function of time
0.1 Gyr 1 Gyr
10 Gyr
Radius distribution as function of time:
Key constraint for planet formation and evolution theory
Radius alone sufficient No mass needed
2
and
Observed version by PLATO come back in 2030 :-)
Have this in 2030 not from theory, but from PLATO data!
Transition solid - gas rich planets• Kepler: numerous close-in small planets: 49% of stars (P<100 d, R<4 REarth)
• Many are low-density planets (likely with a few percent of H/He)
• Important for formation theory, but also habitability
• At which mass and orbital distance is the transition? In principle simple solution with time dimension:
• Solid planets: mean density ~constant in time
• Gaseous planets: mean density increases: contraction, evaporation
• Comparison with spectroscopy and dynamics of multiple planet systems
Not only giants planets
1 Msun star. Initial conditions from population synthesis.
Transition solid - gas rich planets
Search for the transition in the M-rho-t space
Giants: hotter less dense: bloating
Low mass: hotter denser: evaporation
1 10 100 1000 10000Mass [Earth masses]
0.1
1
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Mea
n de
nsity
[g/c
m3 ]
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Equi
libriu
m te
mpe
ratu
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Msin(i) [Earth Mass]
Plan
etar
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ensi
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ram
s/C
entim
eter
s3 ]exoplanets.org | 11/1/2013
exoplanets.org cf. Rauer et al. 2013
Earth like
Pure ice
1 10 100 1000 10000Mass [Earth masses]
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n de
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/cm
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0.1 Gyr
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/cm
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1 10 100 1000 10000Mass [Earth masses]
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[g/c
m3 ]
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/cm
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1 10 100 1000 10000Mass [Earth masses]
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[g/c
m3 ]
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libriu
m te
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Msin(i) [Earth Mass]
Plan
etar
y D
ensi
ty [G
ram
s/C
entim
eter
s3 ]exoplanets.org | 11/1/2013
exoplanets.org cf. Rauer et al. 2013
1 10 100 1000 10000Mass [Earth masses]
0.1
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n de
nsit
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/cm
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10 Gyr
Origin of close-in low-mass planets
• Essential open question for planet formation theory • Rapid migration from beyond the iceline: ice-rich interior • In situ formation or slower migration: rocky interior
• Mass-radius relation degenerate: iron/silicate/ice/H-He
• If we can rule out (observationally) that a sub-population of planets can have a significant H/He atmosphere, break degeneracy
Origin of close-in low-mass planets
Planets with density of 2-3 g/cm3 in the “static” part of the a-R (no time evolution i.e. no H/He envelope) must be icy
Marcy et al. 2014
ObservationSynthetic
Conclusions-PLATO’s ability to accurately determine the ages of the host stars adds a new class of constraints for formation theory
-With the time dimension, it should become possible to observationally see -the transition from solid to gas-rich planets -the composition of close-in low-mass planets
-This constrains several key concepts of planet formation theory like -efficiency of H/He accretion -orbital migration
-The mass is sometimes not necessary for these new constrains: the radius and the age are sufficient