Prsentation PowerPoint

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THE PRIMORDIAL SCULPTING OF THE KUIPER BELT


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SUMMARY FROM LECTURE 1 THE INTRIGUING ASPECTS
OF THE KUIPER BELT THAT NEED TO BE EXPLAINED IN
THE FRAMEWORK OF SOLAR SYSTEM EVOLUTION

• Existence of the resonant Kuiper belt population
• Eccentricity distribution of classical KBOs (and
  weird a,e shape)
• Outer edge of the classical belt
• Co-existence of HOT and COLD classical
  populations with different physical properties
• The mass deficit of the Kuiper Belt

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CAUTION! CELESTIAN MECHANICIANS AT WORK!!
..A PORTFOLIO OF MODELS
Guideline Discuss he mechanisms that, put
together, give a coherent plausible scenario for
the primordial sculpting of the Kuiper
belt .not forgetting about plausible
alternatives.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
Oort Cloud(15)
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
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Planets had to migrate as they depleted the disk
of planetesimals around them.
Ejected!
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A self-consistent numerical simulation
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Origin and orbital distribution of the resonant
population
Mean motion resonance sweeping during Neptune
migration des explain the existence of the
resonant populations and their e,i distribution
(Malhotra, 1993, 1995 Hahn and Malhotra, 1999
Ida et al., 2000 Gomes 2000)
But it cannot explain all the rest (e,i
distribution of the classical belt, outer edge,
mass deficit)
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Origin of the HOT population
A nodal secular resonance might have swept the
belt as the nebula was dissipating, raising the
inclinations (Nagasawa and Ida, AJ, 120 2000).
However, this would work only if the nebula
midplane was different from the planets
midplane. No cold population would be preserved.
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Origin of the HOT population
i 30 20 10 0
An Earth-mass planet scattered by Neptune through
the Kuiper belt can also excite the inclination
(Petit et al., 1999). However the inclination
excitation is not enough and no bi-modal
distribution is produced.
30 40 50
60 Semi major axis (AU)
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Origin of the HOT population
Gomes (2003) again planet migration
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Origin of the HOT population
Gomes, Icarus, 2003
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Origin of the HOT population
Gomes scenario
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Gomes, 2003 Red dots represent the local
population, originally in the 40-50 AU zone Green
dots represent the population coming from
Neptunes region

Explains the inclination distribution of the hot
population, its low mass, its different color
maybe not its e-distribution
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Gomes, 2003 It also explains the origin of the
extended scattered disk at low-a (but not CR105
and Sedna)
2000 CR105
but why is the cold population not massive? Why
an edge at 50 AU?
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Gomes (2003) also showed that part of the
scattered population remains permanently trapped
in the 23 resonance, and well reproduces the
observed distribution (unlike the population
trapped from the classical disk). Consistent
with the color distribution of Plutinos (Hot
population/SD like)
observed
Pluto
simulated
From scattered disk (hot)
From classical disk (cold)
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Origin of the outer edge
Five models proposed

• The existence of a yet undiscovered Martian-mass
  planet orbiting in the 50-70 AU range (Brunini
  and Melita, 2002)
• Prevention of planetesimal accretion beyond 50 AU
  due to MRI turbulence (Balbus et al.)
• Gas-drag migration that moved all growing
  planetesimals from beyond to within 50 AU
  (Weidenschilling)
• Photo-evaporation of the disk due to nearby OB
  stars (Hollenbach et al.)
• A close stellar passage (Ida et al., 2000)

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Forming a 50-70 AU gap with a planet
The planet should still be there, and we should
have already found it ! (Brunini and Melita)
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MRI turbulence preventing planetesimal accretion
Turbulence no gravitational instability
planetesimal formation
? AU
No turbulence gravitational instability
planetesimal formation are possible
Balbus et al.
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Drifting growing planetesimals from the distant
disk
From Weidenschilling
Works also for dust! (Youdin and Shu)
The competition between accretion and gas-drag
induced migration prevents the formation of
sizeable planetesimals beyond ? AU
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Photo-evaporation of the distant disk
Narrow proplyds (disks around new born stars) are
observed in many young stellar associations
Their small sizes are believed to be due to the
photo-evaporation of the distant disk due to the
radiation of nearby OB stars
Hollenbach et al
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Forming the outer edge by a passing Star
The passage of a star at 150-200 AU would have
produced the sharp edge of the Kuiper belt at
50 AU (Ida et al., 2000 Kobayashi and Ida 2001
Melita et al. 2002)
However, severe constraints on the time of the
encounter are provided by the preservation of the
Oort Cloud
/qstar
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Forming the outer edge by a passing Star
A late stellar encounter would strip off the
already formed Oort cloud
(Dones et al.)
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Forming the outer edge by a passing Star
and there would be not enough material left to
form it again. The extended scattered disk with
40ltqlt50 would be as massive as the OC.
(Dones et al.)
A stellar encounter truncating the KB must have
occurred not later than 1 My after the beginning
of Oort cloud formation. Possible/probable in a
stellar cluster?
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Forming the outer edge by a passing Star
A stellar encounter truncating the KB must have
occurred not later than 1 My
This is the kind of encounter that you expect in
a stellar formation region (see simulation by
Bate et al.)
Are the KBOs already formed? Probably not. The
important is that beyond 50 AU the eccentricity
of the particles gets above the limit which
makes collisional damping impossible (Kenyon and
Bromley, 2002)
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Forming the outer edge by a passing Star
Personal opinion Of all the mechanisms presented
above, my preference goes to 2 (turbulence) and
3(planetesimal/dust drift), because they produce
a truncated planetesimal disk without requireing
a truncated protosolar nebula.
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But. Why is the edge at the location of the 12
resonance?
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The mass depletion problem
What depleted the mass of the cold classical
population in the 40-50 AU region? Two possible
ways

• Dynamical way, by exciting the eccentricity of
  most of the objects up to Neptune-crossing values
• Collisional grinding and evacuation of dust by
  radiation pressure

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Depletion by dynamical excitation
T20My
T50My
T100My
e
a (AU)
a (AU)
a (AU)
A massive planetary embryo scattered by Neptune
through the Kuiper belt can explain the mass
depletion and the KB e-distribution (Morbidelli
and Valsecchi, 1997 Petit et al., 1999) However
these simulations did not take into account the
mass of the belt particles. BAD!
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e
M
a
da/dtM
Note on planet migration
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e
M
a
da/dtM
dM -dM1dM2 If dMgt0 then d2a/dt2gt0 forced
migration If dMlt0 then d2a/dt2lt0 damped
migration
Ida et al. (2000, ApJ 534,428)
Note on planet migration
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Why did Neptune stop at 30 AU?
A numerical example
Neptune could have stopped at 30 AU if it started
at about 23 AU and the disk had a moderate mass
(Hahn and Malhotra, 1999). This would leave the
disk in the Kuiper belt zone undepleted.
runaway
damped
Gomes, Morbidelli, Levison, 2003
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Depletion by dynamical excitation
The bodies scattered by the embryo to
Neptune-crossing orbit would have forced Neptune
to migrate well beyond 30AU
30 Earth mass disk in the 10-50 AU range
Earth-mass embryo
To stop Neptune at 30 AU the total mass of the
10-50AU disk had to be lt 15 ME TOO SMALL!
Neptune
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Depletion by dynamical excitation
The bodies scattered by the embryo to
Neptune-crossing orbit would have forced Neptune
to migrate well beyond 30AU
30 Earth mass disk in the 10-50 AU range
Earth-mass embryo
To stop Neptune at 30 AU the total mass of the
10-50AU disk had to be lt 15 ME TOO SMALL!
Neptune
It is not possible to deplete the belt by
ejecting most of its objects to Neptune-crossing
orbit, otherwise Neptune would have migrated well
beyond 30 AU !
GENERAL HUGE IMPLICATION
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Depletion by collisional grinding
Collisional grinding can get rid of most of the
mass provided the eccentricity excitation is
large Stern and Colwell, 1997b but.
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4 potential problems
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• 4 potential problems
• To work, the scenario requires a weird size
  distribution (very steep one down to
  small sizes, so that most of the mass is in small
  bodies, easy to break)
• In their calculations
• Stern and Colwell assume bodies with Dlt200km
• Kenyon assumes a very low Q (inconsistent with
  lab experiments)
• If the collisions favorable for collisional
  grinding are assumed for the entire planetesimal
  disk (5-50 AU), the Oort cloud would not form
  the planetesimals would be destroyed before being
  ejected (Stern and Weissman, Charnoz et al., in
  preparation)

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4 potential problems 2) The excitation of the
cold belt may not be enough for an effective
collisional grinding Gomes (2003) showed that
the mass deficit is a problem for the sole cold
population. The latter has emean 0.05 and
imean2 deg., much smaller than those required in
Stern and Colwells calculations (emean0.25,
imean 7 deg)
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4 potential problems 3) TNO binaries could not
survive the intense collisional process
collisions with bodies 100x less massive than the
satellites would give the latter an impulse
velocity gt escape velocity

• (Petit and Mousis, 2004)

dispersed
survived
dispersed
survived
survived
survived
dispersed
survived
survived
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4 potential problems 4) Collisional grinding
would have driven the ?8 resonance through the
still massive disk. The resonant planetesimals,
once in Neptune crossing orbit might have driven
the planet beyond 30 AU
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we need a change of perspective concerning the
mass depletion problem
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• we need a change of perspective concerning the
  mass depletion problem
• the Kuiper belt was never massive.

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• we need a change of perspective concerning the
  mass depletion problem
• the Kuiper belt was never massive.
• The outer edge of the massive proto-planetary
  disk was somewhere at 30-35 AU.

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• we need a change of perspective concerning the
  mass depletion problem
• the Kuiper belt was never massive.
• The outer edge of the massive proto-planetary
  disk was somewhere at 30-35 AU.

ADVANTAGE I The edge forces the planet to stop
in its vicinity for a wide range of disk masses
(whatever the initial planet position).
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• we need a change of perspective concerning the
  mass depletion problem
• the Kuiper belt was never massive.
• The outer edge of the massive proto-planetary
  disk was somewhere at 30-35 AU.

ADVANTAGE II Massive embryos would have been
caught by Neptune at the disk's edge and
dynamically eliminated.
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The push-out mechanism for the cold population
must be different from that of Gomes (2003) but
not in contradiction with it. it has
to preserve the initial small inclinations.

• Levison and Morbidellis mechanism
• The current cold-belt bodies were captured in the
  12 mean motion resonance with Neptune during the
  migration of the planet
• They moved outward with the resonance while
  Neptune moved
• They were progressively released from the
  resonance due to the non-smoothness of Neptunes
  migration, thus populating the 40-48 AU region

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However, at first sight, this idea cannot work.
The eccentricity of the particles transported by
the 12 resonance increases as they are pushed out
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However, at first sight, this idea cannot work.
The eccentricity of the particles transported by
the 12 resonance increases as they are pushed out
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However, at first sight, this idea cannot work.
The eccentricity of the particles transported by
the 12 resonance increases as they are pushed out
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However, at first sight, this idea cannot work.
The eccentricity of the particles transported by
the 12 resonance increases as they are pushed out
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However, at first sight, this idea cannot work.
The eccentricity of the particles transported by
the 12 resonance increases as they are pushed out
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However, at first sight, this idea cannot work.
The eccentricity of the particles transported by
the 12 resonance increases as they are pushed out
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Nevertheless, in a numerical simulation, it does
work (for a while)
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Q Why doesnt the eccentricity of the resonant
particles increase as predicted by the adiabatic
theory?
Massive case
Not massive case
A Because of the total non-negligible mass of
the resonant particles
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Q Why doesnt the eccentricity of the resonant
particles increase as predicted by the adiabatic
theory?
A Because of the total non-negligible mass of
the resonant particles
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In the numerical simulation the push-out mecanism
stops because the resonance looses its mass too
quickly. But this is probably an artifact of the
grainyness of Neptunes migration, due to the
limited (10,000) number of planetesimals used to
model the disk. In a smoother migration (driven
by a larger number of smaller planetesimal), the
resonance could keep its mass longer and the
push-out scenario could work up to the end.
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Push-out simulation with imposed smooth migration
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Final (a,e) distribution in Levison and
Morbidelli scenario
Smooth migration kicks (5 bodies of ½ Moon mass)
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Final (a,e) distribution in Levison and
Morbidelli scenario
Smooth migration kicks (5 bodies of ½ Moon
mass)
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OPEN PROBLEMS

• Origin and location of the primordial edge
• Origin of the physical differences between the
  hot and cold populations
• Why do the hot and cold populations share
  remarkably similar a,e distributions?
• How uranus reached 20 AU? (see next lecture)

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Recent work by Kobayashi, Ida and Tanaka (Icarus,
in press) propose that a close stellar encounter
truncated the disk and produced the Hot population
The Hot population is produced from the outer
part of the disk (initial agt35 AU). The Cold
population would come later with
Levison-Morbidelli mechanism. Could explain the
physical differences between Hot and Cold pops.
Objects placed by the encounter
Current objects
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Recent work by Kobayashi, Ida and Tanaka (Icarus,
in press) propose that a close stellar encounter
truncated the disk and produced the Hot population
The Hot population is produced from the outer
part of the disk (initial agt35 AU). The Cold
population would come later with
Levison-Morbidelli mechanism. Could explain the
physical differences between Hot and Cold pops.
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Problems with Kobayashi et al. Scenario Q. The
stellar encounter had to occur early. Were the
objects already formed? A. Yes, if they formed
by gravitational instability (not widely
accepted) Q. Why did Neptune stop at 30
AU? A. If the stellar encounter occurred when
the proto-solar nebula was still present the
planets evolution was dominated by the
interaction with the gas and was insensitive to
the presence of crossing planetesimals
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CONCLUSIONS

• THIS IS THE SCENARIO OF THE PRIMORDIAL SCULTPING
  OF THE KUIPER BELT AS THE SPEAKER CURRENTLY
  UNDERSTANDS IT
• The proto-planetary disk was truncated somewhere
  inside 40 AU
• Possibly by orbital decay during planetesimal
  growth
• Neptunes migration did all the rest
• The resonant population (Malhotra, 1993, 1995)
• The Hot population (Gomes, 2003)
• The Cold population (Levison and Morbidelli,
  2003)
• Distant stellar encounters also played a role,
  e.g. for the origin of Sedna