Contact binary
A contact binary is a small body made of two lobes that have gently come together and touch.
A contact binary is an asteroid or comet with two distinct lobes joined at a narrow neck, as if two bodies had drifted together and stuck. Radar and spacecraft images show that many small bodies have this shape.
Famous examples include comet 67P/Churyumov–Gerasimenko, visited by Rosetta, which looks like a rubber duck, and Itokawa, visited by Hayabusa, which looks like a sea otter or a peanut. The Kuiper Belt object Arrokoth, seen by New Horizons in 2019, is made of two flattened lobes that merged very gently, perhaps at walking pace. In 2023 Lucy found that the small moon of asteroid Dinkinesh is itself a contact binary.
Contact binaries form in several ways: a binary pair can slowly spiral together, or a spinning body can split and its pieces reconnect. Their gentle joins show that some collisions in the early Solar System were remarkably slow, very different from the violent impacts that make most meteorites.
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