Download A thousand years old mystery

A thousand years old mystery
Is the moon made of cheese ?
Novel scenarios for the origin and
evolution of the moons
Hagai Perets,
Technion
The Solar system have several
types of moons
Regular satellites of the gas giants
● Irregular satellites of the gas giants
● Moons of Earth and Mars
● Binary planetesimals
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The Solar system have several
types of moons
Regular satellites of the gas giants
● Irregular satellites of the gas giants
● Moons of Earth and Mars
● Binary planetesimals
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Regular satellites
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Regular satellites lie on co-planar circular
orbits aligned with the planet equator
Some of them with a few thousands km
diameter
They orbit the planet at short separations
(< few 0.01 the Hill radius)
Some are found to be in resonance with
each other
Mosqueira &
Estrada 2003
Irregular satellites are eccentric
and/or highly inclined moons
Typically at large separations
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Secular Kozai-Lidov evolution play an
important role in their evolution
Jewitt & Haghighipour (ARAA 2007)
Regular satellites likely form very
similar to terrestrial planets
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Start with a gas/dust
disk
Grow small
planetesimals to big
ones
Migrate, form
resonances
Ogihara & Ida 2012
Irregular satellites are thought to
be captured
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Gas assisted capture -> fine tuned
Ćuk & Gladman (2005)
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Pull-down capture during planet growth
Heppenheimer & Porco (1977)
–
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> fine tuned
Difficulties with Uranus and Neptune
Binary disruption (Agnor & Hamilton 2006) ->inefficient,
maybe explain Triton
Satellite capture during planetary encounters;
somewhat fine tuned;
Nesvorný, Vokrouhlický & Morbidelli 2007
Jewitt & Haghighipour (ARAA 2007)
A new in-situ formation model:
Analogy to planetary systems
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Solar system/Kepler multiple systems
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> Regular satellites
Eccentric and/or inclined systems
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> Irregular satellites
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> Hot Jupiters -> Triton
Origin of eccentric/inclined and hot
Jupiter planetary systems
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Planet-planet scattering (e.g. Rasio & Ford
1996)
Secular evolution due to third
planetary/stellar companions (e.g. Mazeh
et al. 1997)
Important role for tidal friction (e.g. Wu &
Murray 2003)
Formation of satellites at the outer
regions was not modeled
●
The circumplanetary disk should extend up
to R_H
2012
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Where are the external regular satellites ?
In-situ formation of irregular
moons and the role of moon-moon
scattering and secular evolution
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Model multiple large moons in the irregular
moon separation regime
Secular evolution arises naturally due to
perturbations by the Sun
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Model evolution in a gaseous disk
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Model tidal friction by the planet
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Model planet asphericity
In-situ formation of irregular
moons and the role of moon-moon
scattering and secular evolution
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Model multiple large moons in the irregular
moon separation regime
Secular evolution arises naturally due to
perturbations by the Sun
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Model moons formation in the outer disk
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Model evolution in a gaseous disk
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Model tidal friction by the planet
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Model planet asphericity
Perets & Payne, in prep.
Moon-moon scattering:
Disk heating and satellite growth
Perets & Payne, in prep.
Moon-moon scattering:
Formation of prograde irregulars and
runaway moons
Moon-moon scattering:
Temporary re-capture of irregular moons
Moon-moon scattering:
Formation of retrograde irregular moons ?
Origin of some big Solar system
minor-bodies ?
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Ejected moons may have survived to this
day
What kinematic or compositional signature
would we expect ?
The origin of Earth's moon
Earth moon formation theories
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Fission (Darwin)
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Capture (Kuiper)
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Co-accretion
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Giant impact (Hartmann, Canup)
Need to explain: lack of Iron, similar
isotope composition (titanium, oxygen) as
the Earth, inclination,angular momentum
Earth moon formation theories
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Fission (angular momentum, inclination
problem)
Capture (fine tuned, composition)
Co-accretion (Iron core depleted, angular
momentum)
Giant impact (preferred paradigm)
Need to explain: lack of Iron, similar
isotope composition (titanium oxygen) as
the Earth, inclination,angular momentum
The Earth moon formed through a
giant collision...
The Earth-moon composition
problem
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Most of the material comes from the
impactor
Material from different planets suggest very
different composition of the different
planets
The fast-spinning Earth solution
Is the composition problem really
a problem ?
Raymond et al. 2009
Is the composition problem really
a problem ?
Mastrobuono-Battisti & Perets, in prep.
... but the proto-Earth likely had
many previous collisions
Raymond et al. 2009
Earth's previous moons and the
multiple-collisions origin of the moon
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Model a giant impact while a
previous moon exists
Check if previous moons halts
formation of a new moon
Model tidal evolution and
dynamics of two moons
-> SPH
Analytic + N-body
+tides
Model consequent multiple Monte-Carlo
collisions and the collisional (use N-body
growth of the moon
results)
Earth's previous moons and the
multiple-collisions origin of the moon
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Model a giant impact while a
previous moon exists
Check if previous moons halts
formation of a new moon
Model tidal evolution and
dynamics of two moons
-> SPH
Analytic + N-body
+tides
Model consequent multiple Monte-Carlo
collisions and the collisional (use N-body
growth of the moon
results)
New moons can form while
previous one exists
Citron+Perets+Aharonson,
In prep.
Few-body simulations results
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Put a newly formed close single moon;
evolve for a few Myrs
Put a second close moon, and evolve
Shorter period moons tidally evolve faster
and may over run older ones
–
> unstable configuration
–
> Chaotic evolution
~30% of the moons mutually collide, the
rest re-collide with the Earth or ejected
Summary:
Breaking old paradigms of moon formation
An in-situ origin for irregular
satellites instead of capture
scenarios
● Existence of previous moons
of Earth, and a multiplecollisions origin for the Moon
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