A coherent and comprehensive model of the evolution of the

outer solar system

Alessandro Morbidelli (OCA, Nice)Collaborators: R. Gomes, H. Levison, K. Tsiganis, R. Brasser, D. Nesvorny, D. Vokrouhicky, K. Walsh

OUTLINE•

• Motivation

• The Nice model as presented in 2005

• Nice 2 model (2007)

• Nice 2.1 (current)

• Constraining the post-instability evolution of the Giant Planets

MOTIVATION

•

The puzzling aspects of the solar system that we would like to explain

Our giant planets are NOT on circular and co-planar orbits

The eccentricities are much smaller than what we typically see in extra-solar planets, but much larger than expected from formation models.

The strongly excited and depleted Jupiter Trojan population

The strongly excited and depleted Kuiper belt

ERIS

•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

It suggests that a reservoir of small bodies, which remained stable for ~600 My, suddenly became `nuts’.

The Origin of the Late Heavy Bombardment

•

The Nice 2005 model

1) It explains the `spike’ in the bombardment rate, with good magnitude and duration Gomes, Levison, Tsiganis et Morbidelli, 2005. 

II: It explains the current orbits of the giant planets (separation, eccentricities, inclinations) from initial compact quasi-circular and co-planar orbits

K. Tsiganis, R. Gomes, A. Morbidelli, H.F. Levison  2005.    

III: It explains the origin of the Trojans of Jupiter and their orbital distribution and total mass (A. Morbidelli, H.Levison, K.Tsiganis, R.Gomes  2005. )

Simulated Observed

IV: it explains the existence, the structure and the small mass of the Kuiper belt (Levison, Morbidelli, Vanlaerhoven, C., Gomes, R., Tsiganis 2008)

Everything looks great

BUT…•

Two main limitations:

• The initial conditions of the planets are made up

• The location of the inner edge of the disk is somewhat `tuned’ to obtain a late instability

NICE 2007

To understand the orbits that the planets should have had at the beginning of the Nice model, we need to study the evolution of the planets when they are still embedded in a gas disk

Planets migrate!!!

Migration explains the origin of the Hot Jupiters (Lin et al., Nature, 1996)

But we don’t have a Hot Jupiter here, so what happened?

Masset et Snellgrove, 2001; Morbidelli et Crida, 2007; Pierens and Nelson, 2008

3:2 res

Once Jupiter and Saturn are stuck in their 3:2 resonance, Uranus et Neptune are in turn trapped in resonances with Saturn (Morbidelli, Tsiganis, Crida, Levison et Gomes, 2007)

We found a total of 6 possible configurations for the giant planets, (all in resonance with each other). Four of them are stable once the gas disk is dissipated (and in absence of planetesimas)

When planetesimals are added, the planets may be extracted from their resonances and become unstable, finally reaching orbits similar to the current once as in the original Nice model (Morbidelli et al., 2007)

If the inner edge of the planetesimal disk is well tuned, this instability can occur late, after hundreds of My as in the original Nice model

•

The dependence of the instability time on the location of the inner edge of the disk is even more critical than before…

Great…….BUT

NICE 20xx

A self-gravitating trans-Neptunian planetesimal disk…..

(Levison et al., in preparation)

….leads in a natural way to late instabilities, quite independently of the location of the inner edge of the disk

…The simulations where Saturn is removed, typically leave Jupiter on an orbit with an eccentricity typical of extra-solar giant planets

The planets are “saved” in 15-20% of the runs, and when they do their final orbits are pretty good.

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Constraining the giant planets evolution after the trigger of their instability

a

e

Two possible evolutions from instability:

I) The divergent evolution of Jupiter and Saturn is dominated by planetesimal-driven migration

Typical timescale for Jupiter-Saturn separation: 10My

The divergent migration of Jupiter and Saturn drives secular resonances across the terrestrial planets region and the asteroid belt. If this migration takes as long as a few My, this:

i) Makes the terrestrial planets too eccentric or even unstable

Brasser et al., 2009

The divergent migration of Jupiter and Saturn drives secular resonances across the terrestrial planets region and the asteroid belt. If this migration takes as long as a few My, this:

ii) Gives the asteroid belt a really weird orbital distribution

simulatedreal

a

e

Two possible evolutions from instability:

II) The divergent evolution of Jupiter and Saturn is dominated by encounters with Uranus or Neptune

Divergent migration takes << My

This kind of evolution occurs in ~10% of the successful runs in Nice 2005 and > 50% of those of Nice 20xx

Example of Jumping-Jupiter evolution

Nesvorny et al. (2007) argued that Jupiter-Uranus encounters did occur, otherwise only Saturn, Uranus and Neptune (NOT Jupiter) should have irregular satellites

If the “jump” is large enough, then the secular resonance sweep too fast to have a disruptive effect (Brasser et al., 2009)

…the same is true for the asteroid belt

simulatedreal

CONCLUSIONS•The structure of the outer Solar System and the LHB require a late shake-up of the giant planets orbits

•Our understanding of how this happened (initial configuration, trigger mechanism…) is still evolving (Nice 2005, 2007, 20xx….)

•The Nice 2007 model is quite appealing because it links gas-disk-driven dynamics with planetesimal-driven dynamics. It also explains why we do not have a hot Jupiter here

•In the Nice 20xx model, even the delay becomes generic

•There is no trace of giant planet migration in the inner solar system. We believe that this implies that Jupiter had a very rapid evolution due to encounters with U/N

•The problem is that the favorable evolutions (of jumping-Jupiter type with large enough jump and all planets saved at the end on reasonable orbits) occur only in ~ 5-10% of the cases