A numerical check of the Collisional Resurfacing scenario Philippe Thébault & Alain Doressoundiram Observatoire de Meudon

Color Dispersion within the Kuiper Belt

- Correlated to orbital parameters ¤ inclination ¤ eccentricities (?) ¤ periastron ¤ V rms = (e 2 + i 2 ) 1/2 V kep

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 V rms =(e 2 +i 2 ) 1/2. V Kep But it’s more complicated than this …

Problems with a local V rms 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 AU region placed in the identified stable regions embedded in a swarm of ¤ test impactors bodies Close encounter search algorithm => estimate coll and E cin for each impact on a target At the end of the run, we compare  E cin 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

d) SKBO only (academic)

¤ moderate correlation with e ¤ Weak correlation with i ¤ Strong correlation with q ¤ V rms correlation with large dispersion ¤ « bluer » plutinos Results / case 1

¤ Weak correlation with e ¤ Weak correlation with i ¤ moderate correlation with q ¤ V rms correlation with large dispersion ¤ « bluer » plutinos Results / case 2

¤ moderate correlation with e ¤ Weak correlation with i ¤ moderate correlation with q ¤ V rms correlation with large dispersion ¤« bluer » outer disc bodies Results / case 3

No significant correlations Results / case 4

eccentricityinclination q Case 1: 48 AU cutoff0.33 ( )0.12 (0.05)0.48 ( ) Case 2: exicted outer disc0.27 ( )0.14 (0.015)0.28 ( ) Case 3: « cold » outer disc0.41 ( )0.16 ( )0.38 ( ) Case 4: SKBO only0.12 ( )0.06 (0.55)-0.07 (0.24) Correlations between  E cin 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 V rms 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, V rms … ( i ) c.f. color indexes in the« real » belt numerical estimations of inhomogeneities of the collisional activity within the KB