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A numerical check of the
Collisional Resurfacing scenario
Philippe Thébault & Alain Doressoundiram
Observatoire de Meudon
Color Dispersion within the Kuiper Belt
Color Dispersion within the Kuiper Belt
- Correlated to orbital parameters
¤ inclination
¤ eccentricities (?)
¤ periastron
¤ Vrms = (e2 + i2)1/2 Vkep
Possible explanations
• Intrinsic physical differences within the early KB
•Coexistence of 2 distincs populations
¤ Excited objects originating from the a < 30 AU region
¤ indigenous « Cold » objects
•Collisional resurfacing
Unlikely because of too weak physical gradients in KBO region
- Surface Reddening by space wethearing
(sun radiative processing, sun or galactic cosmic rays,…)
-Mutual Collisions
resurfacing by fresh « gray » material
The collisional resurfacing scenario
• Competing effect between
Requires both mechanisms to act on comparable timescales
The collisional resurfacing scenario
While space weathearing should act ~homogeneously throughout the KB, the level of collisional resurfacing should strongly depend on KBO’s excitations and positions
Collisional resurfacing should leave a signature that might be tracked
Could it explain the observed correlation with orbital parameters?
To a first approximation:
Search for a link between color-index and objects’ excitation
Vrms=(e2+i2)1/2.VKep
But it’s more complicated than this …
Problems with a local Vrms analysis…
Need for a more complete study, taking into account spatial distributions and mutual interactions
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 ?…
Deterministic code following the evolution of test particles under the gravitational pull of Sun+4giant-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 => estimate <dv>coll 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.
Numerical Procedure
The target population
The impactor population
a) cut-off at 48 AU
The impactor disc
b) extended excited disc
c) extended « cold » disc
The impactor population
The impactor population
d) SKBO only (academic)
¤ moderate correlation with e
¤ Weak correlation with i
¤ Strong correlation with q
¤ Vrms correlation with large dispersion
¤ « bluer » plutinos
Results / case 1
¤ Weak correlation with e
¤ Weak correlation with i
¤ moderate correlation with q
¤ Vrms correlation with large dispersion
¤ « bluer » plutinos
Results / case 2
¤ moderate correlation with e
¤ Weak correlation with i
¤ moderate correlation with q
¤ Vrms correlation with large dispersion
¤« bluer » outer disc bodies
Results / case 3
No significant correlations
Results / case 4
eccentricity inclination qCase 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)
Correlations between Ecin and orbital parameters
(Spearman’s rank correlation coefficient)
Similarities with color-index distribution in the « real » belt
Global statistical correlations
with e, i, q and Vrms
but…
¤ Stronger correlation with e than with i
BUT other features strongly contradict the observed correlations:
¤ tendency towards highly impacted (« bluer ») plutinos
-« out of plane effect »
- more structure in e than in i
Possible explanations
• simplicity of the numerical model?
• better understanding of the physical processes at play
Long range effect of the space weathering
continuous reddening or formation of a neutral mantle?
different collisional environment in the plutino region?
too academic impactor discs ?
• give up the C.R. scenario in favour of an alternative explanation
Can these contradictions be explained within the frame of the C.R. scenario?
• but problems with the spatial localisation of
highly collisional regions “gray” KBOs localisation
Conclusions
• general statistical correlations with e,q, Vrms… ( i )
c.f. color indexes in the« real » belt
numerical estimations of inhomogeneities of the collisional activity within the KB