Newfound moon around asteroid Dinkinesh is actually two touching rocks

Asteroid Dinkinesh’s newly discovered moon is actually a contact binary, with two objects lightly touching at each end. This is the first time such a binary star has been discovered orbiting another asteroid.

Dinkinesh was the first rock visited by NASA’s Lucy spacecraft, which passed on November 1st. As the spacecraft passed, it discovered a small rock orbiting Dinkinesh, which the Lucy team tentatively named Serum.

However, as Lucy transmits more data to Earth, it becomes clear that Serum is not just a single object. Instead, it looks like two rocks of similar size connected at the edges, resulting in a sort of peanut-like shape. In the images from Lucy, one leaf of the asteroid must have been hidden behind the other, which is why the team initially missed it.

“All of these rocks will be independent, but I have to admit that I never expected to see bilobed moons like this,” he says. Hal Levison Director of the Lucy Mission at the Southwest Research Institute in Colorado. “There are some things about it that I don’t understand.”

First, the process that forms these small satellites is not expected to produce multiple satellites of the same size, Levison says. Also, rather than the two being connected as is, If they had fully merged, they would have had to collide at extremely low speeds.

“These small objects are like laboratories for all the physics we need to understand how solid bodies grow and become planets,” Levison says. Serum’s strange properties could indicate that there’s something wrong with current ideas about how planets formed, he says.

Over the course of the remaining mission, Lucy will visit eight more asteroids. Among them she will visit her seven asteroids, one in the main asteroid belt and then sharing Jupiter’s orbit, called the Trojans. Levison said additional satellites and other surprises are almost certainly in store. “Each of these systems is unique and has undergone its own evolution, so I would be surprised if we didn’t find a lot of unexpected things,” he says.