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A numerical check of the Collisional Resurfacing
scenario
Philippe Thébault Alain Doressoundiram Observ
atoire de Meudon
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Color Dispersion within the Kuiper Belt
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Color Dispersion within the Kuiper Belt
- Correlated to orbital parameters
inclination eccentricities (?)
periastron Vrms (e2 i2)1/2 Vkep
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Possible explanations

• Intrinsic physical differences within the early
  KB

Unlikely because of too weak physical gradients
in KBO region

• Coexistence of 2 distincs populations
• Excited objects originating from the a lt 30 AU
  region
• indigenous  Cold  objects

• Collisional resurfacing

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The collisional resurfacing scenario

• Competing effect between

• Surface Reddening by space wethearing
• (sun radiative processing, sun or galactic
  cosmic rays,)

• Mutual Collisions
• resurfacing by fresh  gray  material

Requires both mechanisms to act on comparable
timescales
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The collisional resurfacing scenario
While space weathearing should act homogeneously
throughout the KB, the level of collisional
resurfacing should strongly depend on KBOs
excitations and positions
Could it explain the observed correlation with
orbital parameters?
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To a first approximation Search for a link
between color-index and objects
excitation Vrms(e2i2)1/2.VKep
But its more complicated than this
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Problems with a local Vrms analysis
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GOAL Numerically estimate the relative spatial
distribution of kinetic energy received by
collisions within the KB search for
similarities with the relative distribution of
color-index
do the regions of  bluer  KBOs match the
regions of higher collisional activity ?
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Numerical Procedure
Deterministic code following the evolution of
test particles under the gravitational pull of
Sun4giant-planets. 2 populations 500 test
target bodies in the 38-55 AU region placed in
the identified stable regions embedded in a
swarm of 2500-5000 test impactors bodies
Close encounter search algorithm gt estimate
ltdvgtcoll and Ecin for each impact on a target At
the end of the run, we compare ?Ecin for each
target and derive a spatial map of the relative
amount of kinetic energy received by collisions
within the numerical system.
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The target population
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The impactor population
a) cut-off at 48 AU
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The impactor disc
b) extended excited disc
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The impactor population
c) extended  cold  disc
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The impactor population
d) SKBO only (academic)
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Results / case 1
moderate correlation with e Weak correlation
with i Strong correlation with q Vrms
correlation with large dispersion  bluer 
plutinos
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Results / case 2
Weak correlation with e Weak correlation with
i moderate correlation with q Vrms
correlation with large dispersion  bluer 
plutinos
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Results / case 3
moderate correlation with e Weak correlation
with i moderate correlation with q Vrms
correlation with large dispersion  bluer 
outer disc bodies
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Results / case 4
No significant correlations
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Correlations between ? Ecin and orbital parameters
eccentricity inclination q
Case 1 48 AU cutoff 0.33 (3.10-2) 0.12 (0.05) 0.48 (4.10-25)
Case 2 exicted outer disc 0.27 (8.10-8) 0.14 (0.015) 0.28 (5.10-8)
Case 3  cold  outer disc 0.41 (2.10-15) 0.16 (4.10-3) 0.38 (4.10-2)
Case 4 SKBO only 0.12 (4.10-3) 0.06 (0.55) -0.07 (0.24)
(Spearmans rank correlation coefficient)
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Similarities with color-index distribution in the
 real  belt
Global statistical correlations with e, i, q
and Vrms
but
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BUT other features strongly contradict the
observed correlations
Stronger correlation with e than with i
- out of plane effect 
- more structure in e than in i
tendency towards highly impacted ( bluer )
plutinos
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Possible explanations

• simplicity of the numerical model?

too academic impactor discs ?
different collisional environment in the
plutino region?

• better understanding of the physical processes
  at play

Long range effect of the space weathering continu
ous reddening or formation of a neutral mantle?

• give up the C.R. scenario in favour of an
  alternative explanation

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Conclusions
numerical estimations of inhomogeneities of the
collisional activity within the KB

• general statistical correlations with e,q, Vrms
  ( i )
• c.f. color indexes in the real  belt

• but problems with the spatial localisation of
• highly collisional regions ? gray KBOs
  localisation

Can these contradictions be explained within the
frame of the C.R. scenario?
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