NASA’s Lucy observes binary orbiting asteroid for the first time.

In a surprising twist of discovery, as NASA’s Lucy spacecraft transmitted data from its first encounter with the asteroid Dinkinesh on November 1, 2023, the scientific team uncovered an unexpected revelation about Dinkinesh’s satellite. It turns out that the satellite is a contact binary, consisting of two smaller objects touching each other. This newfound perspective provides the first documented instance of a contact binary orbiting another asteroid.

When the initial images of Dinkinesh and its satellite were received, the two lobes of the contact binary coincidentally appeared to be aligned from Lucy’s viewpoint at closest approach. However, as additional images captured around the encounter were transmitted, the true nature of this object became evident.

“Contact binaries seem to be fairly common in the solar system,” stated John Spencer, Lucy’s deputy project scientist, who is based at the Southwest Research Institute in Boulder, Colorado. “We haven’t seen many up-close, and we’ve never seen one orbiting another asteroid. We’d been puzzling over odd variations in Dinkinesh’s brightness that we saw on approach, which gave us a hint that Dinkinesh might have a moon of some sort, but we never suspected anything so bizarre!”

Lucy’s primary mission objective is to survey the Jupiter Trojan asteroids, which have never been visited before. The encounter with the small main belt asteroid Dinkinesh was added to the mission in early 2023 to serve as a test of the system that enables the spacecraft to continuously track and image its asteroid targets as it swiftly flies past them. The unexpected revelation was made possible by the system’s excellent performance during the Dinkinesh encounter, allowing the team to capture multiple views of the system, gaining a better understanding of the asteroids’ shapes.

“This discovery is puzzling, to say the least,” said Hal Levison, the principal investigator for Lucy, also affiliated with the Southwest Research Institute. “I would have never expected a system that looks like this. In particular, I don’t understand why the two components of the satellite have similar sizes. This is going to be fun for the scientific community to figure out.”

Tom Statler, Lucy’s program scientist at NASA Headquarters, remarked, “It’s truly marvelous when nature surprises us with a new puzzle. Great science pushes us to ask questions that we never knew we needed to ask.”

The scientific team continues to receive and process additional data from the Lucy spacecraft’s encounter with Dinkinesh and its satellite. Dinkinesh and its satellite are the first of the 11 asteroids that Lucy is scheduled to explore during its 12-year mission. Following its passage near the inner edge of the main asteroid belt, Lucy is currently on a trajectory back toward Earth for a gravity assist in December 2024. This close flyby will provide the necessary velocity for Lucy to navigate through the main asteroid belt and observe asteroid Donaldjohanson in 2025, before reaching the Trojan asteroids in 2027.

Lucy’s principal investigator is based at the Southwest Research Institute in Boulder, Colorado, with overall mission management provided by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Lockheed Martin Space, located in Littleton, Colorado, was responsible for building and operating the spacecraft. Lucy represents the 13th mission in NASA’s Discovery Program, with NASA’s Marshall Space Flight Center in Huntsville, Alabama, managing the program for the Science Mission Directorate at NASA Headquarters in Washington.