A contact binary satellite of the asteroid (152830) Dinkinesh
Authors: Levison Harold F. , Marchi Simone , Noll Keith S. , Spencer John R. , Statler Thomas S. , Bell James F. , Bierhaus Edward B. , Binzel Richard , Bottke William F. , Britt Daniel , Brown Michael E. , Buie Marc W. , Christensen Philip R. , Dello Russo Neil , Emery Joshua P. , Grundy William M. , Hahn Matthias , Hamilton Victoria E. , Howett Carly , Kaplan Hannah , Kretke Katherine , Lauer Tod R. , Manzoni Claudia , Marschall Raphael , Martin Audrey C. , May Brian H. , Mottola Stefano , Olkin Catherine B. , Pätzold Martin , Parker Joel Wm. , Porter Simon , Preusker Frank , Protopapa Silvia , Reuter Dennis C. , Robbins Stuart J. , Salmon Julien , Simon Amy A. , Stern S. Alan , Sunshine Jessica M. , Wong Ian , Weaver Harold A. , Adam Coralie , Ancheta Shanti , Andrews John , Anwar Saadat , Barnouin Olivier S. , Beasley Matthew , Berry Kevin E. , Birath Emma , Bolin Bryce , Booco Mark , Burns Rich , Campbell Pam , Carpenter Russell , Crombie Katherine , Effertz Mark , Eifert Emily , Ellis Caroline , Faiks Preston , Fischetti Joel , Fleming Paul , Francis Kristen , Franco Ray , Freund Sandy , Gallagher Claire , Geeraert Jeroen , Gobat Caden , Gorgas Donovan , Granat Chris , Gray Sheila , Haas Patrick , Harch Ann , Hegedus Katie , Isabelle Chris , Jackson Bill , Jacob Taylor , Jennings Sherry , Kaufmann David , Keeney Brian A. , Kennedy Thomas , Lauffer Karl , Lessac-Chenen Erik , Leonard Rob , Levine Andrew , Lunsford Allen , Martin Tim , McAdams Jim , Mehall Greg , Merkley Trevor , Miller Graham , Montanaro Matthew , Montgomery Anna , Murphy Graham , Myers Maxwell , Nelson Derek S. , Ocampo Adriana , Olds Ryan , Pelgrift John Y. , Perkins Trevor , Pineau Jon , Poland Devin , Ramanan Vaishnavi , Rose Debi , Sahr Eric , Short Owen , Solanki Ishita , Stanbridge Dale , Sutter Brian , Talpas Zachary , Taylor Howard , Treiu Bo , Vermeer Nate , Vincent Michael , Wallace Mike , Weigle Gerald , Wibben Daniel R. , Wiens Zach , Wilson John P. , Zhao Yifan 
Published: May 2024

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 evolution2. (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 spectrum3,4 is typical of bodies in this part of the main belt5. Here we report observations by the Lucy spacecraft6,7 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.