Asteroid ‘Dinky’ Visited by NASA’s Lucy Spacecraft Found To Have Contact Binary Moon

Experts have proposed a model that shows how a twin moon was created around asteroid Dinkinesh. This is the first contact binary moon ever discovered.

Twin Moons Stuck Together

In November 2023, NASA's Lucy spacecraft flew past its first official target - a binary main-belt asteroid named Dinkinesh. It is one of the 11 asteroids that Lucy plans to explore over its 12-year journey.

Also known as "Dinky," this cosmic rock is actually not alone in space. Lucy discovered that a satellite asteroid dubbed "Selam" revolves around Dinky. This moon was named after the child counterpart of the Lucy hominin fossil found in 1974.

As the spacecraft sent more data back to Earth, astronomers discovered that Selam was not just a single moon but two moons stuck together. The unexpected finding was published in the paper "A contact binary satellite of the asteroid (152830) Dinkinesh."

Led by astronomy and geology professor Jessica Sunshine from the University of Maryland, the Lucy team noted that the strange arrangement challenges current theories about the formation of asteroids and other cosmic objects. It also offers additional insight into the dynamics, internal structure, and evolutionary history of both Dinkinesh and Selam.

With the additional observations taken by Lucy, the scientists were able to better explore features like the rotation speed of Dinkinesh and the orbit pattern of Selam. They also gained a better understanding of the kind of materials they are possibly made of, bringing them closer to learning the secrets of the creation of terrestrial bodies.

Lucy spacecraft provided images which revealed a trough on Dinky where a quarter of its body separated from the asteroid. It was actually a ridge created after the structural failure of the asteroid.

How Did Binary Moons Form?

Dinky is known to have fast spinning motion which is assumed to be the result of uneven reflection of sunlight on its surface. Sunshine and colleagues theorize that this accelerated movement caused Dinky to shed and release rocky debris into orbit. At the same time, some of the fragments aggregated to form Selam, and another portion of the debris rained back down on the asteroid as boulders, creating the ridges photographed by Lucy.

It is widely accepted that planets form when smaller celestial bodies like asteroids run into each other as they orbit the Sun. Their tendency to break apart or stick together depends on their strength and internal structure. The research team believed that Dinky may have some internal strength, which enabled it to maintain most of its structure.

How Dinkinesh formed unusual dual moons still remains a mystery. Still, Sunshine and her team believe that their research findings can unlock the door to comparative studies with similar cosmic bodies.

For instance, the Didymos binary system can be compared to this ultra-rare double moon, especially since they share similar properties like general shape, size, and composition. While the Didymos binary system has very different features from the Dinkinesh system, they may have undergone similar processes to become what they are today.