A contact binary satellite of the asteroid (152830) Dinkinesh
Harold F. Levison, S. Marchi, Keith Noll, J. R. Spencer, Thomas S. Statler, J. F. Bell, E. B. Bierhaus, Richard P. Binzel, W. F. Bottke, D. T. Britt, Michael E. Brown, M. W. Buie, P. R. Christensen, Neil Dello Russo, Joshua P. Emery, W. M. Grundy, M. Hahn, V. E. Hamilton, Carly Howett, H. H. Kaplan, Katherine A. Kretke, Tod R. Lauer, C. Manzoni, Raphael Marschall, Audrey Martin, B. May, S. Mottola, C. B. Olkin, M. Pätzold, J. W. Parker, Simon Porter, Frank Preusker, Silvia Protopapa, Dennis C. Reuter, S. J. Robbins, Julien Salmon, Amy Simon, S. A. Stern, J. M. Sunshine, Ian Wong, H. A. Weaver, Coralie D. Adam, Shanti Ancheta, John P. Andrews, Saadat Anwar, O. S. Barnouin, Matthew Beasley, Kevin Berry, Emma Birath, Bryce Bolin, Mark Booco, Rich Burns, P. S. Campbell, Russell Carpenter, Katherine Crombie, Mark Effertz, Emily Eifert, C. Ellis, Preston Faiks, Joel T. Fischetti, Paul J. Fleming, Kristen Francis, Ray Franco, Sandy Freund, Claire Gallagher, J. Geeraert, Caden Gobat, Donovan Gorgas, Chris Granat, Sheila Gray, P. Haas, A. Harch, Katie Hegedus, Chris Isabelle, Bill Jackson, Taylor Jacob, S. H. M. Jennings, D. E. Kaufmann, Brian A. Keeney, T. Kennedy, Karl Lauffer, Erik J. Lessac‐Chenen, Rob Leonard, Andrew H. Levine, Allen Lunsford, Tim Martin, Jim McAdams, G. Mehall, Trevor F. Merkley, Graham Miller, Matthew Montanaro, Anna B. Montgomery, G. A. Murphy, Maxwell Myers, Derek Nelson, Adriana Ocampo, Ryan Olds, John Pelgrift, Trevor Perkins, Jon P. Pineau
Abstract
Abstract Asteroids with diameters less than about 5 km have complex histories because they are small enough for radiative torques (that is, YORP, short for the Yarkovsky–O’Keefe–Radzievskii–Paddack effect) 1 to be a notable factor in their evolution 2 . (152830) Dinkinesh is a small asteroid orbiting the Sun near the inner edge of the main asteroid belt with a heliocentric semimajor axis of 2.19 au ; its S-type spectrum 3,4 is typical of bodies in this part of the main belt 5 . Here we report observations by the Lucy spacecraft 6,7 as it passed within 431 km of Dinkinesh. Lucy revealed Dinkinesh, which has an effective diameter of only 720 m, to be unexpectedly complex. Of particular note is the presence of a prominent longitudinal trough overlain by a substantial equatorial ridge and the discovery of the first confirmed contact binary satellite, now named (152830) Dinkinesh I Selam. Selam consists of two near-equal-sized lobes with diameters of 210 m and 230 m. It orbits Dinkinesh at a distance of 3.1 km with an orbital period of about 52.7 h and is tidally locked. The dynamical state, angular momentum and geomorphologic observations of the system lead us to infer that the ridge and trough of Dinkinesh are probably the result of mass failure resulting from spin-up by YORP followed by the partial reaccretion of the shed material. Selam probably accreted from material shed by this event.