Abstract
Following its flyby and first imaging of the Pluto–Charon binary, the New Horizons spacecraft visited the Kuiper belt object (KBO) 2014 MU69 (also known as (486958) Arrokoth). The imaging showed MU69 to be a contact binary that rotates at a low spin period (15.92 hours), is made of two individual lobes connected by a narrow neck and has a high obliquity (about 98 degrees)1, properties that are similar to those of other KBO contact binaries inferred through photometric observations2. However, all scenarios suggested so far for the origins of such configurations3,4,5 have failed to reproduce these properties and their probable frequent occurrence in the Kuiper belt. Here we show that semi-secular perturbations6,7 operating on only ultrawide KBO binaries close to their stability limit can robustly lead to gentle, slow binary mergers at arbitrarily high obliquities but low rotational velocities, reproducing the characteristics of MU69 and other similar oblique contact binaries. Using N-body simulations, we find that approximately 15 per cent of all ultrawide binaries with a cosine-uniform inclination distribution5,9 are likely to merge through this process. Moreover, we find that such mergers are sufficiently gentle to deform the shape of the KBO only slightly. The semi-secular contact binary formation channel not only explains the observed properties of MU69, but may also apply to other Kuiper belt or asteroid belt binaries and in the Solar System and extra-solar moon systems.
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Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
Change history
22 May 2020
A Correction to this paper has been published: https://doi.org/10.1038/s41586-020-2351-4
References
Stern, S. A. et al. Initial results from the New Horizons exploration of 2014 MU69, a small Kuiper belt object. Science 364, eaaw9771 (2019).
Lacerda, P. A change in the light curve of Kuiper belt contact binary (139775) 2001 QG298. Astron. J. 142, 90–98 (2011).
Goldreich, P., Lithwick, Y. & Sari, R. Formation of Kuiper belt binaries by dynamical friction and three-body encounters. Nature 420, 643–646 (2002).
Richardson, D. C. & Walsh, K. J. Binary minor planets. Annu. Rev. Earth Planet. Sci. 34, 47–81 (2006).
Perets, H. B. & Naoz, S. Kozai cycles, tidal friction, and the dynamical evolution of binary minor planets. Astrophys. J. Lett. 699, 17–21 (2009).
Antonini, F. & Perets, H. B. Secular evolution of compact binaries near massive black holes: gravitational wave sources and other exotica. Astrophys. J. 757, 27–40 (2012).
Grishin, E., Perets, H. B. & Fragione, G. Quasi-secular evolution of mildly hierarchical triple systems: analytics and applications for GW sources and hot Jupiters. Mon. Not. R. Astron. Soc. 481, 4907–4923 (2018).
Grishin, E., Perets, H. B., Zenati, Y. & Michaely, E. Generalized Hill-stability criteria for hierarchical body systems at arbitrary inclinations. Mon. Not. R. Astron. Soc. 466, 276–285 (2017).
Naoz, S., Perets, H. B. & Ragozzine, D. The observed orbital properties of binary minor planets. Astrophys. J. 719, 1775–1783 (2010).
Lidov, M. L. The evolution of orbits of artificial satellites of planets under the action of gravitational perturbations of external bodies. Planet. Space Sci. 9, 719–759 (1962).
Kozai, Y. Secular perturbations of asteroids with high inclination and eccentricity. Astron. J. 67, 591–598 (1962).
Naoz, S. The eccentric Kozai–Lidov effect and its applications. Annu. Rev. Astron. Astrophys. 54, 441–489 (2016).
Fabrycky, D. & Tremaine, S. Shrinking binary and planetary orbits by Kozai cycles with tidal friction. Astrophys. J. 669, 1298–1315 (2007).
Porter, S. B. & Grundy, W. M. KCTF evolution of trans-Neptunian binaries: connecting formation to observation. Icarus 220, 947–957 (2012).
Veillet, C. et al. The binary Kuiper-belt object 1998 WW31. Nature 416, 711–713 (2002).
Petit, J. M. et al. The extreme Kuiper belt binary 2001 QW322. Science 322, 432–434 (2008).
Luo, L., Katz, B. & Dong, S. Double-averaging can fail to characterize the long-term evolution of Lidov–Kozai cycles and derivation of an analytical correction. Mon. Not. R. Astron. Soc. 458, 3060–3074 (2016).
Rein, H. & Liu, S.-F. REBOUND: an open-source multi-purpose N-body code for collisional dynamics. Astron. Astrophys. 537, A128 (2012).
Rein, H. & Spiegel, D. S. IAS15: a fast, adaptive, high-order integrator for gravitational dynamics, accurate to machine precision over a billion orbits. Mon. Not. R. Astron. Soc. 446, 1424–1437 (2015).
McKinnon, W. B. et al. The solar nebula origin of (486958) Arrokoth, a primordial contact binary in the Kuiper belt. Science 367, eaay6620 (2020).
Thirouin, A. & Sheppard, S. S. Light curves and rotational properties of the pristine cold classical Kuiper belt objects. Astron. J. 157, 228–247 (2019).
Parker, A. H. & Kavelaars, J. J. Collisional evolution of ultra-wide trans-Neptunian binaries. Astrophys. J. 744, 139–152 (2012).
Perets, H. B. Binary planetesimals and their role in planet formation. Astrophys. J. Lett. 727, 3 (2011).
Funato, Y., Makino, J., Hut, P., Kokubo, E. & Kinoshita, D. The formation of Kuiper belt binaries through exchange reactions. Nature 427, 518–520 (2004).
Heggie, D. C. Binary evolution in stellar dynamics. Mon. Not. R. Astron. Soc. 173, 729–787 (1975).
Grundy, W. et al. Mutual orbit orientations of transneptunian binaries. Icarus 334, 62–78 (2019).
Schäfer, C. et al. A smooth particle hydrodynamics code to model collisions between solid, self-gravitating objects. Astron. Astrophys. 590, A19 (2016).
Goldreich, P., Lithwick, Y. & Sari, R. Planet formation by coagulation: a focus on Uranus and Neptune. Annu. Rev. Astron. Astrophys. 42, 549–601 (2004).
Nesvorný, D., Li, R., Youdin, A. N., Simon, J. B. & Grundy, W. M. Trans-Neptunian binaries as evidence for planetesimal formation by the streaming instability. Nat. Astron. 3, 808–812 (2019).
Canup, R. M. A giant impact origin of Pluto–Charon. Science 307, 546–550 (2005).
Murray, C. D. & Dermott, S. F. Solar System Dynamics (Cambridge Univ. Press, 1999).
Liu, B., Muñoz, D. J. & Lai, D. Suppression of extreme orbital evolution in triple systems with short-range forces. Mon. Not. R. Astron. Soc. 447, 747–764 (2015).
Grishin, E., Lai, D. & Perets, H. B. Chaotic quadruple secular evolution and the production of misaligned exomoons and warm Jupiters in stellar multiples. Mon. Not. R. Astron. Soc. 474, 3547–3556 (2018).
Tremaine, S., Touma, J. & Namouni, F. Satellite dynamics on the Laplace surface. Astron. J. 137, 3706–3717 (2009).
Thirouin, A., Noll, K. S., Ortiz, J. L. & Morales, N. Rotational properties of the binary and non-binary populations in the trans-Neptunian belt. Astron. Astrophys. 569, A3 (2014).
Wandel, O. J., Schäfer, C. M. & Maindl, T. I. Collisional fragmentation of porous objects in planetary systems. In Proc. 1st Greek–Austrian Workshop Extrasolar Planetary Systems (eds Maindl, T. I., Varvoglis, H. & Dvorak, R.) 225–242 (2017).
Haghighipour, N., Maindl, T. I., Schäfer, C. M. & Wandel, O. J. Triggering the activation of main-belt comets: the effect of porosity. Astrophys. J. 855, 60 (2018).
Speith, R. Improvements of the Numerical Method of Smoothed Particle Hydrodynamics. Habilitation thesis, Univ. of Tübingen (2006)
Dvorak, R., Maindl, T. I., Burger, C., Schäfer, C. & Speith, R. Planetary systems and the formation of habitable planets. Nonlinear Phenom. Complex Syst. 18, 310–325 (2015).
Maindl, T. I. et al. Impact induced surface heating by planetesimals on early Mars. Astron. Astrophys. 574, A22 (2015).
Haghighipour, N., Maindl, T. I., Schäfer, C., Speith, R. & Dvorak, R. Triggering sublimation-driven activity of main belt comets. Astrophys. J. 830, 22 (2016).
Schäfer, C. M. et al. Numerical simulations of regolith sampling processes. Planet. Space Sci. 141, 35–44 (2017).
Burger, C., Maindl, T. I. & Schäfer, C. M. Transfer, loss and physical processing of water in hit-and-run collisions of planetary embryos. Celestial Mech. Dyn. Astron. 130, 2 (2018).
Malamud, U., Perets, H. B., Schäfer, C. & Burger, C. Moonfalls: collisions between the Earth and its past moons. Mon. Not. R. Astron. Soc. 479, 1711–1721 (2018).
Malamud, U., Perets, H. B., Schäfer, C. & Burger, C. Collisional formation of massive exomoons of superterrestrial exoplanets. Mon. Not. R. Astron. Soc. 492, 5089–5101 (2020).
Malamud, U. & Perets, H. B. Tidal disruption of planetary bodies by white dwarfs – I: A hybrid SPH-analytical approach. Mon. Not. R. Astron. Soc. 492, 5561–5581 (2020).
Malamud, U. & Perets, H. B. Tidal disruption of planetary bodies by white dwarfs – II: Debris disc structure and ejected interstellar asteroids. Mon. Not. R. Astron. Soc. 493, 698–712 (2020).
Herrmann, W. Constitutive equation for the dynamic compaction of ductile porous materials. J. Appl. Phys. 40, 2490–2499 (1969).
Carroll, M. & Holt, A. C. Suggested modification of the P–α model for porous material.J. Appl. Phys. 43, 759–761 (1972).
Jutzi, M., Michel, P., Hiraoka, K., Nakamura, A. M. & Benz, W. Numerical simulations of impacts involving porous bodies. II. Comparison with laboratory experiments. Icarus 201, 802–813 (2009).
Leleu, A., Jutzi, M. & Rubin, M. The peculiar shapes of Saturn’s small inner moons as evidence of mergers of similar-sized moonlets. Nat. Astron. 2, 555–561 (2018).
Jutzi, M., Benz, W., Toliou, A., Morbidelli, A. & Brasser, R. How primordial is the structure of comet 67P? Combined collisional and dynamical models suggest a late formation. Astron. Astrophys. 597, A61 (2017).
Rotundi, A. et al. Dust measurements in the coma of comet 67P/Churyumov–Gerasimenko inbound to the sun. Science 347, aaa3905 (2015).
Malamud, U. & Prialnik, D. Modeling Kuiper belt objects Charon, Orcus and Salacia by means of a new equation of state for porous icy bodies. Icarus 246, 21–36 (2015).
Lorek, S., Gundlach, B., Lacerda, P. & Blum, J. Comet formation in collapsing pebble clouds. What cometary bulk density implies for the cloud mass and dust-to-ice ratio. Astron. Astrophys. 587, A128 (2016).
Fulle, M. et al. The dust-to-ices ratio in comets and Kuiper belt objects. Mon. Not. R. Astron. Soc. 469, S45–S49 (2017).
Jutzi, M., Benz, W. & Michel, P. Numerical simulations of impacts involving porous bodies. I. Implementing sub-resolution porosity in a 3D SPH hydrocode. Icarus 198, 242–255 (2008).
Grady, E. D. & Kipp, E. Dynamic fracture and fragmentation. In High-Pressure Shock Compression of Solids (eds Asay, J. R. & Shahinpoor, M.) 265–322 (Springer, 1993).
Benz, W. & Asphaug, E. Impact simulations with fracture. I – Method and tests. Icarus 107, 98 (1994).
Benz, W. & Asphaug, E. Catastrophic disruptions revisited. Icarus 142, 5–20 (1999).
Jutzi, M. SPH calculations of asteroid disruptions: the role of pressure dependent failure models. Planet. Space Sci. 107, 3–9 (2015).
Collins, G. S., Melosh, H. J. & Ivanov, B. A. Modeling damage and deformation in impact simulations. Meteorit. Planet. Sci. 39, 217–231 (2004).
Acknowledgements
We acknowledge discussions with D. C. Fabrycky and E. Kite. H.B.P. acknowledges support from the MINERVA Center for Life Under Extreme Planetary Conditions and the Kingsley Fellowship at Caltech. C.M.S. and O.W. acknowledge support by the High Performance and Cloud Computing Group at the Zentrum für Datenverarbeitung of the University of Tübingen, the state of Baden-Württemberg through bwHPC and the German Research Foundation (DFG) through grant number INST 37/935-1 FUGG. C.M.S. acknowledges support from the DFG through grant number 398488521.
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E.G. led the project, performed the analytic calculations and ran and analysed the N-body simulations. U.M. led the hydrodynamical modelling, its analysis and wrote the hydrodynamical sections. H.B.P. initiated the project and supervised it, suggested the main ideas and concepts and took part in all of the analysis. O.W. ran the hydrodynamical simulations and was the main developer of the porosity module in the hydrodynamical code. C.M.S. developed the hydrodynamical code and supervised the development of the porosity module. E.G. and H.B.P. wrote the main text.
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Extended data figures and tables
Extended Data Fig. 1 Additional results of the collision models.
a, 40° impact angle, medium-strength material. b, 40° impact angle, low-strength material. c, d, Low-density model (0.5 g cm−3) with an impact angle of 55° and medium-strength material. The edge (c) and face (d) views are given.
Extended Data Fig. 2 Additional results of the collision models.
5° impact angle, high-strength material and large escape velocity, v = 10vesc.
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Grishin, E., Malamud, U., Perets, H.B. et al. The wide-binary origin of (2014) MU69-like Kuiper belt contact binaries. Nature 580, 463–466 (2020). https://doi.org/10.1038/s41586-020-2194-z
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DOI: https://doi.org/10.1038/s41586-020-2194-z
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