Asteroids, Comets, Meteors (2012) 6056.pdf

DYNAMICAL EVOLUTION OF HAUMEA COLLISIONAL FAMILY AND IMPLICATIONS FOR THE OUTER SOLAR SYSTEM. P. S. Lykawka1, J. Horner2, T. Mukai3 and A. M. Nakamura3, 1 Astronomy Group, Faculty of Social and Natural Sciences, Kinki University, Japan ( [email protected] ), 2 Dept. of Astrophysics, School of Physics, University of New South Wales, Australia, 3 Dept. of Earth and Planetary Sciences, Kobe Uni- versity, Japan.

Introduction: Trans-neptunian objects (TNOs) or- neptunian belt: classical and detached (majority), res- biting in the trans-neptunian belt (or Edge- onant (<10%), and scattered (<1%). In particular, the worth-Kuiper belt) carry precious information about fraction of resonant fragments is sensitive to the tim- the origin and evolution of the solar system. More re- ing of the collision and orbital history of Neptune. cently, the first collisional family was identified in the ● If the ejection velocities of the fragments are belt, thus providing evidence of the importance of col- strongly dependent on their size, the larger fragments lisions between TNOs. The family consists of the will likely be more tightly clustered in orbital element dwarf planet (136108) Haumea (formerly 2003 EL61) space than their smaller counterparts within the trans- located at semimajor axis, a ~ 43 AU (currently neptunian belt. locked in the 12:7 mean motion resonance), and at ● Approximately 25-40% of the fragments ac- least nine other ~100 km-sized TNOs located around quired unstable orbits, and were subsequently lost a = 42-44.5 AU. Haumea is also one of the largest from the solar system. However, we do not expect TNOs known to date, with an estimated diameter of slowly diffusing unstable fragments to contribute sig- ~1500 km. The ten family members concentrate in or- nificantly to the currently known populations of Cen- bital elements at a = 42-44.5 AU, q = 37-39 AU and i taurs and short period comets.

= 24-29° and share the peculiar C-depleted and H2O ice rich surface spectra with Haumea’s. Here, based on current knowledge of the family and asteroid collision physics, we modeled the long term orbital evolution of an ensemble of fragments with varied sizes after the collision that created Haumea’s family over 4 Gyr. Three realistic scenarios of kinetic energies carried by the fragments were considered, represented by mean

ejection velocities veje = 200, 300 and 400 m/s. Each theoretical family of fragments was modeled with 1600 particles, whose orbits were evolved for 4 Gyr under the gravitational perturbation of the giant plan- ets and the most massive family members in supple- mentary calculations. We also tested other model parameters. Conclusions: ● We can reproduce the orbital distribution of the currently known members of the Haumean collisional family. However, the model suggests that the family fragments appear spread over a wide range of orbital The orbital distributions in a-e-i element space of representative theor- elements: ∆a ~ 6-11 AU; ∆e ~ 0.1-0.17; ∆i ~ 7-11°. etical Haumean collisional families after 4 Gyr for the three main scen- This provides predictions for new family members arios considered in this work, modeled with ejecta fragments following with future observations. a mean ejection velocity of 200, 300 and 400 m/s. Currently known ● The orbital diffusion of the stable theoretical Haumea collisional family members are shown with red squares. family fragments over 4 Gyr is extremely small. Therefore, the observed orbital distribution of Acknowledgments: PSL gratefully acknowledge Haumea’s family can be used to draw conclusions the use of the General Purpose cluster at the National about the nature of the collision that originated the Observatory of Japan (NAOJ) to perform the calcula- family. tions presented in this work. JH acknowledges the fin- ● The theoretical family fragments were found to ancial support of the Australian Research Council, populate all four dynamical classes within the trans- through the ARC discovery grant DP774000.