[1] The existence of contact binary asteroids was first speculated by planetary scientist Allan F. Cook in 1971, who sought for potential explanations for the extremely elongated shape of the Jupiter trojan asteroid 624 Hektor, whose longest axis measures roughly 300 km (190 mi) across and is twice as long as its shorter axes according to light curve measurements.
[2] Astronomers William K. Hartmann and Dale P. Cruikshank performed further investigation into Cook's contact binary hypothesis in 1978 and found it to be a plausible explanation for Hektor's elongated shape.
In 2002–2003, then-graduate student Scott S. Sheppard and his advisor David C. Jewitt observed the KBO and plutino 2001 QG298 with the University of Hawaiʻi's 2.24-m telescope at Mauna Kea, as part of a survey dedicated to measuring the light curves of KBOs.
[9] The contact binary nature of comets was first suspected after the Deep Space 1 spacecraft's flyby of 19P/Borrelly in 2001, which revealed a bilobate peanut-shaped nucleus with a thick neck connecting the two lobes.
[12]: 499 Later radar imaging and spacecraft exploration of the Jupiter family comet 103P/Hartley in 2010 also revealed a thick-necked, peanut-shaped nucleus similar to 19P/Borelly.
[14]: 167 For doubly-synchronous binary systems with 1 km (0.62 mi)-diameter components, the tangential and radial impact velocities when they collide are less than 50 mm/s (2.0 in/s), which are low enough to not disrupt the shapes of the two bodies.
[14]: 167 In 2007, Daniel J. Scheeres proposed that contact binary asteroids in the NEA population can undergo rotational fissioning after being rotationally accelerated by the YORP effect.
[14]: 167 In the trans-Neptunian region and especially the Kuiper belt, binary systems are thought to have formed from the direct collapse of gas and dust from the surrounding protoplanetary nebula due to streaming instability.
[19] In 2022, Anne Virkki and colleagues published an analysis of 191 near-Earth asteroids (NEAs) that were observed by the Arecibo Observatory radar from December 2017–2019.
A stellar occultation by the KBO 19521 Chaos on 29 March 2023 revealed that it had an apparently bilobate shape 380 km (240 mi) across, which could potentially make it the largest known contact binary object in the Solar System.
[30] Among the distant minor planets, the icy Kuiper belt object Arrokoth was confirmed to be a contact binary when the New Horizons spacecraft flew past in 2019.
[1] The small main-belt asteroid 152830 Dinkinesh was confirmed to have the first known contact binary satellite after the Lucy probe flew by it on November 1, 2023.