Prsentation PowerPoint

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THE FORMATION OF THE OORT CLOUD
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• Historic paper Duncan, Quinn Tremaine, 1977,
  AJ 94, 1330
• combination of Monte Carlo and direct
  integrations
• initial conditions a2,000AU, e0.99

• Work re-done by Dones, Levison, Duncan
  Weissman, Icarus, in press. 2005.
• Direct numerical integrations
• Initial conditions 5ltalt40 AU, e0, i0
• 4 giant planets, galactic tide, passing stars
• No planet migration
• No gas
• Current galactic environment
• Current tide
• Stellar density 0.041Msun/pc3, 0.11lt Mlt18.24
  Msun, 1.7 lt vrel lt 158 km/s (median 46 km/s)
  52,648 encounters within 1pc in 4Gy??

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RECIPE TO FORM AN OORT CLOUD
Galaxy mass distribution
The planets expell the comets from their
neighbourhood on orbits with moderate inclination
relative to the Solar System plane.
60o
Solar system plane
Thus, the comets have a large inclination
relative to the galactic plane. They feel a
strong disk tide
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RECIPE TO FORM AN OORT CLOUD
Dynamics of a comet with a10,000 AU under the
galactic tide
Comet in Oort cloud (peri lifted from the planet
region)
Comet propelled to the inner solar system
Comet coupled to Uranus
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RECIPE TO FORM AN OORT CLOUD
Galaxy mass distribution
The galactic tide changes i and e
Enhance e
60o
Solar system plane
Precession about the galactic frame
Raise q
Raise of q captures in Oort cloud Enhancement in
e pushes the comet to the interior of the Solar
System
The precession around the axis orthogonal to the
galactic plane can turn a ecliptic prograde comet
into a retrograde one
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An example of evolution
a
q
Stellar encounters
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Making the Oort cloud a,q evolution
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Key snapshots
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Making the Oort cloud a,igalactic evolution
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Making the Oort cloud a,iecliptic evolution
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Key snapshots
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Another example of evolution
a
q
q decreases to less than 10 AU (interacts with
Saturn)
Stellar encounter
Correlated q,i oscillations (notice shorter
period than before because a is larger)
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A third example of evolution
a
q
q 10 AU
Late insertion in the Oort cloud
Stellar encounter
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Incursions to qlt10 AU are fairly typical
Running means
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If qlt 10 AU, T gt 100 K Stern et al., (2000)
detected Ar in Hale-Bopp, which argues that the
comet (or at least its interior) has never been
at Tgt 35-40 K Weaver et al. (2002) searched three
other long-period comets and found no evidence of
Ar.
Consistent with simulated scatter in qmin?
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qlt10 AU DOES NOT IMPLY deep encounters with Saturn
Distant encounters with Saturn or deep encounters
with Uranus or Neptune are the main players in
Oort cloud formation. Deep encounters with
Jupiter or Saturn eject the comet to the
interstellar space
agt20,000 AU
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Jupiter (and Saturn) kills
The typical energy kick provided to the comet
during a close encounter with Jupiter or Saturn
is 10-3. Thus the comets evolves in a random
walk with jumps ?(1/a)10-3 However, the Oort
cloud is 10-4 wide only in 1/a The comets
kicked by Jupiter and Saturn jump over the Oort
cloud. This is NOT the case of comets kicked by
Uranus or Neptune, or suffering distant
encounters with Saturn.
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Oort cloud injection probability as a function of
initial location
agt20,000 AU
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THE STRUCTURE OF THE OORT CLOUD
as it comes out from the simulations
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Scattered disk
Hills cloud
isotropic
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Solar system plane
20,000 AU
Galactic plane
100,000 AU
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Mass distribution in the Oort cloud
n(r) r-3 Roughly equal masses in Inner and
Outer Oort clouds
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Mass evolution as a function of time
Peaks _at_ 9My (Jupiters disk)
Overall efficiency 5.5
ignore
20x
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PROBLEM I
Outer Oort cloud 1012 comets (H10lt11) H1011
D2.3 km ?0.6 g/cm3 D2.3km
M4x1015g Size distribution D-2 for 2ltDlt11km
mean mass4x1016g
Weissman (1996), based on 1P/Halley
Hence, the Outer Oort cloud should contain
4x1028g 7M?
Efficency to build the Outer Oort cloud 2.5
Thus the disk had to be
270 M?
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• its a lot!
• Numerical simulations (see next lecture) show
  that, with such a massive, disk Neptune would
  have migrated too far away, and Jupiter and
  Saturn would have migrated passed their mutual
  25 resonance. These simulations imply that the
  disk was 35-50 M?
• Ways out ?
• Comets may be less dense than 0.6g/cm3
  The density of
  19P/Borrelly is 0.18-0.30 g/cm3 (Davidson and
  Gutierrez, 2004). Is this typical of ALL comets?
• Increase the Oort cloud capture efficiency (see
  next)

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PROBLEM II
Outer Oort cloud 1012 comets
(H10lt11) Scattered Disk 3x108 comets (H10lt9)
109 comets (H10lt11) (assuming that the
cumul. H-distribution has exponent 0.28
(Weissman, Lowry, 2001)
Hence, the observed ratio Outer Oort cloud /
Scattered disk 103
According to the Oort cloud formation
simulations, the ratio Outer Oort
cloud / Scattered disk 10 (!!!)
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POSSIBLE SOLUTION (to both problems) the
environment of the young Sun was much denser than
the current one (more stellar encounters
stronger tide) Fernandez, 1997
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• If the decoupling of comets from the planetary
  system occurs for a103-103.5 AU this means that
• A more massive and bounded Inner Oort cloud is
  formed
• More mass can be stored in the Oort cloud overall
• Jupiter and Saturn can be more effective in
  placing comets in the Oort cloud

• If Neptune is not the main contributor to the
  Oort cloud, the ratio OC / SD is enhanced

GOOD IDEA JULIO!
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(No Transcript)
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Numerical simulations of the formation of the
Oort cloud in a dense environment have been done
by Fernandez and Brunini (Icarus 145, 580 2000)

• They assumed three kinds of environment
• Loose cluster 10 stars/pc3
• Dense cluster 25 stars/pc3
• Superdense cluster 100 stars/pc3
• In all cases, stars are Solar Mass current star
  environment 0.041 MS/pc3
• Most runs assumed a placental gas of 105 H2/cm3
  (current density 3 H2/cm3 )
• Encounter velocities 1km/s (current ones
  40km/s)
• Planetesimals i.cs. à la DQT87 (large a100-200,
  q in planet zone)

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Fernandez-Brunini results
From U,N
From J,S

• The denser the environment, the more bound is the
  Oort cloud.
• However, the Outer Oort cloud (that active today)
  is totally empty
• Thus the idea may work provided that
• There is a way to move Inner OC comets to the
  Outer OC
• The inner OC is very massive

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The overall efficiency is increased by a factor
25-10 with respect to DLDW (but not relative to
DQT). Is it the solution of the mass problem?
However, the contribution from Jupiter-Saturn
zone is still minimal (comets from J,S region
land in a part of the OC where they are stripped
away by the stellar encounters) the paradox of
the OC/SD ratio remains
DQT87
DLDW
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SEDNA and 2000 CR105 evidence for a dense
environment?
SEDNA
2000 CR105
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SEDNA and 2000 CR105 evidence for a dense
environment?
SEDNA
EMPTY
2000 CR105
Observational biases 1/P1/a3/2 would strongly
favor the discovery of bodies in the empty zone,
if they existed
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In the current environment the orbits of Sedna or
2000 CR105 would not be produced.
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531
74
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We need a mechanism that lifts the peri of bodies
only beyond 200-500 AU. A dense galactic tide
can do this
Dense cluster
Loose cluster
From Jupiter zone From Uranus zone
Sedna
From Fernandez-Brunini, 2000
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Simulation of the emplacement of Sedna and 2000
CR105 from the scattered disk, due to a solar
mass star passing at 800 AU with 1km/s
encounter velocity (Morbidelli and Levison, 2004)
Jovian SD _at_ 9My, from DLDW simulations
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Effect of the stellar encounter distance. For a
MMs, q800 AU. For M1/10 MS, q400 AU.
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The stellar encounter had to happen early (i.e.
in the first few My), otherwise the Oort cloud
would be too anemic.
Example stellar encounter 1Gy
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Total mass placed in Sedna-like orbit Mass of
the Scattered disk in the 400ltalt600 AU range
from DLDW simulations, it is at
most 0.5 of the mass of the initial planetesimal
disk (50 M?), thus 0.25 M? The lifting
efficiency
from our
simulations 0.8 Therefore, the total mass in
Sedna-like orbit can be at most 0.2 M?
According to Mike Brown Sedna could have been
spotted along 1 of its orbit 100
Sednas The survey covered 1/5 of the total sky
500 Sednas (if i isotropic) Assuming the KB
size distribution 5 M? in Sedna-like orbit !!
BIG UNCERTAINTY could very well be 0.1 M?
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Capture of Sedna from the protoplanetary disk of
a low mass star (Morbidelli, Levison, 2004)
Sun
Resulting heliocentric velocity (parabolic)
Velocity w.r.t. Sun (weakly hyperbolic)
Velocity w.r.t. brown dwarf
Brown dwarf
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Capture of Sedna from the protoplanetary disk of
a low mass star (Morbidelli, Levison, 2004)
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The capture efficiency can be high 30-40 of the
planetesimal disk between 20-100 AU, if the
inclination of the disk relative to the Sun-dwarf
orbital plane is small (lt30). Drops at high-i.
Brown dwarfs and low mass stars have IR excess
(signature of a protoplanetary disk). However, do
they have planetesimals the size of Sedna?
Unswer unknown!
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CONCLUSIONS

• The formation of the Oort cloud is,
  qualitateively, a well-understood process
• From the quantitative point of view, however, two
  big problems remain unsolved.
• It is reasonable that the solar system formed in
  a dense environment (cluster).
• Sednas orbit can be the witness of such
  environment
• It is unclear yet if the dense environment could
  solve the Oort cloud problems
• Open topic of research