The newly discovered moon of asteroid Dinkinesh is actually a contacting binary – two objects that are lightly touching at their ends. This is the first time that such a binary has been found orbiting another asteroid.
Dinkinesh was the first rock seen by NASA’s Lucy spacecraft, which flew by on November 1. As the spacecraft passed by, it found a small rock orbiting Dinkinesh, which the Lucy team tentatively named Salaam.
But as Lucy sends more data back to Earth, it becomes clear that Salaam is not just an object. Instead, it appears to be two similarly sized rocks joined at the end, resulting in a sort of peanut shape. The team missed it at first because in Lucy’s images, one of the asteroid’s lobes would be hidden behind the other.
“All these rocks are going to be their own individuals, but I have to admit I never would have expected such a bilobed satellite,” says Hal Levison at the Southwest Research Institute in Colorado, head of the Lucy mission. “There are many things about it that I don’t understand.”
The processes that shaped these small satellites are not expected to create multiples of the same size, Levison says. Furthermore, both should be connected as they are Having completely merged, they would have collided at extremely low speeds.
“These small bodies are kind of the laboratories of all the physics we need to try to understand how solid bodies became planets,” says Levison. He says Salaam’s strange properties may indicate something is not right about our current ideas about the formation of planets.
During the rest of its mission, Lucy is scheduled to visit eight more asteroids – one in the main asteroid belt, and then seven asteroids that share Jupiter’s orbit, called Trojans. Levison says there are almost certainly more additional satellites and other surprises in store. “Each of these systems is unique, it’s gone through a unique evolution, so I’d be surprised if we don’t find a lot of things we’re not expecting,” he says.