Constraining the final merger of contact binary (486958) Arrokoth with soft-sphere discrete element simulations

• DOI: 10.5194/epsc2020-378
• Publication Date: 2020-10-08T10:21:39Z
• Authors: Julian C. Marohnic; Derek C. Richardson; William B. McKinnon; Harrison F. Agrusa; Joseph V. DeMartini; Andrew F. Cheng; S. Alan Stern; Cathy B. Olkin; Harold A. Weaver; John R. Spencer
• Keywords: Earth and Planetary Astrophysics (astro-ph.EP); 0103 physical sciences; FOS: Physical sciences; 01 natural sciences; Astrophysics - Earth and Planetary Astrophysics; 0105 earth and related environmental sciences

In 2019, the New Horizons spacecraft flew by Kuiper belt object (486958) Arrokoth, a member of cold classical population in belt. Images returned from flyby reveal that Arrokoth is contact binary composed two distinct lobes joined narrow region (the "neck"). The are roughly similar to oblate spheroids shape and long axis whole body about 35 km [1]. Cold objects like thought be among most primitive bodies our solar system, forming their current positions nebula over 4 Gyr ago remaining nearly undisturbed since. mechanism which formed thus great interest may lend unique insight into formation terrestrial outer system. Under assumption union progenitor bodies, we use numerical code model final stage merger created this object. We investigate range possible parameters results determine plausible scenarios. describe methods used simulate detail results. work presented here described greater Marohnic et al. 2020, press for Icarus special issue on science [2].We parallel N-body 'pkdgrav' [3]. pkdgrav uses soft-sphere discrete element method (SSDEM) compute collisions between spherical particles. SSDEM resolves contacts allowing particles interpenetrate slightly as proxy deformation. Restoring forces modeled damped springs static, rolling, twisting friction accounted well. Both separately, "rubble piles" total, each simulated event 100,000 200,000 Our simulations test effects varying impact angle speed, material cohesion strength, shape, bulk density, spin (see Figure 1).                                                                                                                                                                                       1: A gentle rubble-pile formerly close, synchronous orbit. preserved, neck-like area remains well-defined.   The suite suggest any could produce an would have been quite slow (roughly equal mutual escape speed or slower) at near-grazing angle. find scenario gradual inspiral close orbit leading final, merger.Acknowledgements: were performed Deepthought 2 cluster University Maryland, College Park. This was supported NASA grant NNX15AH90G awarded Solar System Workings program, Maryland Graduate School Research Scholarship Award, NASA's project via contracts NASW-02008 NAS5-97271/TaskOrder30. [1]: Stern, S.A., Weaver, H.A., Spencer, J.R., Olkin, C.B., Gladstone, G.R., Grundy, W.M., Moore, J.M., Cruikshank, D.P., Elliott, McKinnon, W.B. Parker, J.W., 2019. Initial exploration 2014 MU69, small Belt Science, 364(6441).[2]: Marohnic, J.C., Richardson, D.C., W.B., Agrusa, H.F., DeMartini, J.V., Cheng, A.F., H.A. 2020. Constraining with simulations. Icarus, p.113824.[3]: Stadel, J.G., 2001. Cosmological analysis (Doctoral dissertation, Washington).