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Origin of the orbital architecture of the planets of the Solar System

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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
• 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
The puzzling aspects of the solar
system that we would like to explain
Our giant planets are
NOT on circular and coplanar orbits
The eccentricities are
much smaller than what
we typically see in extrasolar planets, but much
larger than expected
from formation models.
The strongly excited and depleted Jupiter Trojan population
The strongly excited and depleted Kuiper belt
The Origin of the Late Heavy Bombardment
•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 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. )
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
Two main limitations:
• The initial conditions of the planets
NICE 2007
are made up
• The location of the inner edge of the
disk is somewhat `tuned’ to obtain a
late instability
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
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.
Constraining the giant planets
evolution after the trigger of their
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
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
•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
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