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Can CO CV Meteorites Come from the Eos Family?

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Can CO CV Meteorites Come from the Eos Family? 60th Annual Meteoritical Society Meeting 5049.pdf Can CO/CV meteorites come from the Eos family? Eos asteroid family is one of the largest groupings in the main b elt [1] and currently its memb ership consists of more than 480 ob jects [2]. The family is cut by the 9:4 mean-motion resonance with Jupiter, and 5 resonant asteroids have b een found within this resonance [3]. The family memb ers b elong to the rare K taxonomic class and show a sp ectral app earance in b etween C- and S-typ e asteroids [4,5]. Many authors suggest, on the basis of sp ectra and alb edo similarities, that K-typ e asteroids mayhave a mineralogical comp osition close to that of the anhydrous CO/CV carb onaceous chondrites [6,7,8]; however, the sp ec- trum of 221 Eos do es not show clear evidence for the calcium-aluminium-rich inclusions CAI absorption features typical of CO meteorites [9]. In order to test the link b etween CO/CV meteorites and K-typ e aster- oids, in the context of the broader GAPTEC pro ject [10], wehave b egan a massive and long-term numerical integration of a sample of synthetic ob jects aimed at simulating real family memb ers injected into the 9:4 mean-motion resonance. In this analysis, we use the SWIFT RMVS3 integrator package [11,12]. The chaotic region asso ciated with the 9:4 mean-motion resonance spans at least the region b etween 3.026 AU and 3.032 AUatlow eccentricityi.e. < 0.06 and mo derately low inclination 10 values, corresp onding to the lo cation of the Eos family.At presentwehave followed the dynamical evolution of all particles for 120 Myr forwards, one of them 78 for 139 Myr. Required eccentricity for an ob ject inside this resonance to b ecome a Mars crosser is 0.45, whereas values as large as 0.70 allow it to b ecome a Jupiter crosser. This di erence, together with the fact that the rate of increase of eccentricity due to resonant e ects is very small, allows Mars to extract the vast ma jority of particles from the resonance as so on as they b ecome Mars crossers, therefore losing the protection mechanism with re- sp ect to Jupiter encounters. At that stage most of the particles will b ecome Jupiter controlled, and will b e very probably ejected from the Solar System. Since the eccentricity required to b ecome an Earth crosser is 0.65, the ob jects can, in principle, exp erience Earth encounters b efore they havea chance to approach Jupiter. As a consequence, some ob jects can b ecome Earth controlled and can show a secular decrease in semi-ma jor axis. As a preliminary result, one of the simulated ob jects was found to follow a line of constant Tisserand parameter with resp ect to the Earth and for a short time to Venus, eventually colliding with our planet after 139.4 Myr. 1 60th Annual Meteoritical Society Meeting 5049.pdf Our simulation gives strong constraints for what concerns the orbital elements and the collisional history of CO/CV meteorites. Since only ab out 1 of the particles shows an evolved orbit semi-ma jor axis <2AU in a timescale to o long for accounting meteoritic material coming directly from the resonance, as consequence, the semi-ma jor axis and eccentricity of CO/CV meteorites fallen on the Earth should b e of the order of 3 AU and 0:65, resp ectively . Considering that the time required to achievean Earth-crossing orbit is at least 50 Myr and the fact that the collisional life- p time in Myr of a meteoroid is prop ortional to r where r is the radius in cm [12], therefore resulting in 10Myr for a b o dy metre-sized, meteorites coming out from 9:4 resonance must have su ered a collisional-cascade pro- cess. In spite of the fact that 92 of the test particles that have b een \depleted" [10] were found to b e ejected from the Solar System, the huge amountof material provided by the catastrophic impact that pro duced the Eos family, whose clue is the IRAS dust band asso ciated with the family, can yield for the 2 of CO/CV meteorite falls on the Earth. References: [1] Hirayama K. 1918 Astron. J., 31, 185-188. [2] Zappal a V. et al. 1995 Icarus, 116, 291-314. [3] Morbidelli A. et al. 1995 Icarus, 118, 132-154. [4] Tedesco E.F. et al. 1989 Astron. J., 97, 580-606. [5] Granahan J.C. et al. 1993 LPS, XXIV, 557. [6] Britt et al. 1992 Icarus, 99, 153-166. [7] Granahan J.C., 1993 PhD Thesis. [8] Doressoundiram A. et al. 1997 Icarus, submitted. [9] Cloutis E.A. and Ga ey M.J. 1993 Icarus, 105, 568-579. [10] Gladman B.J. et al. 1997 Science, submitted. [11] Wisdom J. and Holman M. 1991 Astron. J., 102, 1528-1538. [12] Levison H.F. and Duncan M. 1994 Icarus, 108, 18-36. [13] Wetherill G.W. 1988 Icarus, 76, 1-18. 2.
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