Towards a comprehensive evolution model for the outer solar system
“Towards a comprehensive evolution model for the outer solar system” or... the “Nice II” model
In collaboration with: A. Morbidelli, H. Levison, R. G...
“Towards a comprehensive evolution model for the outer solar system” or... the “Nice II” model
In collaboration with: A. Morbidelli, H. Levison, R. Gomes & R. Brasser, D. Nesvorny
Overview Why did we need a new view/model for the OSS The Nice model (v1.0, 2005) What were the main problems of this model? The v1.5 Nice model (2007) Planet-disc interaction revisited → Nice II model... Conclusions
Why did we need a new model for the OSS? in situ formation of U and N is highly unlikely → planet migration... smooth migration cannot explain the observed (e,I)'s
not high (as for EPS) but much higher than formation models give...
Why did we need a new model for the OSS? The strongly depleted and excited Kuiper belt asteroids, Trojans, ...
Why did we need a new model for the OSS? The origin of the Late Heavy Bombardment (LHB)
•Cataclysmic event triggered 3,9 Gy ago, ~600My after terrestrial planet formation •Global event: traces found on Mercury, Venus, Earth, Mars, Vesta…., possibly on giant planets satellites •20.000x the current bombardment rate: 1 km object impacting the Earth every 20 years! •Duration: 50-150 My
The Nice model (v1.0 - 2005) Planets more closely packed than before → resonances come to play... an initially stable configuration → planet-disk interactions force smooth migration resonance crossing excites eccentricities → global instability Instability suppressed by dispersing the disk → mass depletion
1J=2S resonance crossing
The Nice model (v1.0 - 2005)
… and the LHB main characteristics
Several “success” stories since: trojans, irregular satellites, KBOs, primitive main-belt asteroids, ... reproduces the orbits of the planets...
What were the problems with the Nice model? Initial conditions for the planets were simply made-up... ●
… they should represent the “final” conditions of a previous phase of gas-driven migration Critical (although monotonic) dependence on tcrit with disk parameters ●
The v1.5 Nice model (2007) J-S migration in a gas disk (first ~3 My) can lead to capture in a 3:2 MMR (Masset & 3:2 res
Snellgrove 2001, Pierens & Nelson 2008)
J-S can stop migrating after that, for a range of reasonable disk parameters (Morbidelli & Crida 2007)
… all four outer planets can be trapped in a multiple (Laplace-type) resonance (Morbidelli et al., 2007) → “proper” initial conditions (see also Batygin & Brown 2010)
Planetesimals can then extract the planets from their resonance and... … force them to migrate, cross MMRs (e.g. 5:3) → evolution similar to Nice I GREAT initial conditions WORSE for having a delayed instability → the planets are “pealing off” the inner edge of the disk but without moving in a → needs extreme fine tunning of the disk to get tcrit ~ 700 My
Planet-disk interactions revisited What is missing in all these simulations ? → the disk's self-gravity → particle-particle velocity stirring Gives secular energy exchange between the disk and the planets!
move sunwards ...
… Nice II model Eccentricity of Uranus increases (due to 2:3 with S) ...
… until a critical value (~0.07) for which the critical argument of the 3:4 with Neptune starts circulating → U-N unlocked from MMR → the system becomes unstable!
… Nice II model
t50%= 730 My
Planetesimal encounters
Systems go unstable preferentially LATE – 9/21 in 1 Gy – t50% = 730 My Not a sensitive dependence on the inner edge of the disk! Both “Proper” initial conditions and GREAT timing for the LHB.
Conclusions We are converging (slowly) towards a “Nice II” model Basic ingredients: Nice v1.5 initial conditions + self-gravitating disc → consistent with previous phase of gas-driven migration → late instabilities naturally provided by a slow planet-disk energy exchange + break-up of a resonance (needs more work...) (+) Point: it should work similarly for all configurations found by Morbdelli et al (2007) and Batygin & Brown (2010) (-) Point: not all configurations have the same “success” rate... → we're looking into this....
a closer look to some ISS constraints... Divergent planet migration leads to variation of the secular frequencies → resonances between g5 and gi (i=2,4) are possible
If migration was slow (~ 10 My) or resonances were approached slowly → possibly devastating effect on terrestrial planets and asteroids
a closer look to some ISS constraints... This favors “fast” planet migration → dominated by planet-planet encounters → a subset of Nicemodel runs
The terrestrial planets (and asteroids) are not significantly affected ...