On Nov. 1, NASA’s Lucy spacecraft flew by not just its first asteroid, but its first two. The first images returned by Lucy reveal that the small main belt asteroid Dinkinesh is actually a binary pair.

“Dinkinesh really did live up to its name; this is marvelous,” said Hal Levison, referring to the meaning of Dinkinesh in the Amharic language, “marvelous.” Levison is principal investigator for Lucy from the Boulder, Colorado, branch of the San-Antonio-based Southwest Research Institute. “When Lucy was originally selected for flight, we planned to fly by seven asteroids. With the addition of Dinkinesh, two Trojan moons, and now this satellite, we’ve turned it up to 11.”

In the weeks prior to the spacecraft’s encounter with Dinkinesh, the Lucy team had wondered if Dinkinesh might be a binary system, given how Lucy’s instruments were seeing the asteroid’s brightness changing with time. The first images from the encounter removed all doubt. Dinkinesh is a close binary. From a preliminary analysis of the first available images, the team estimates that the larger body is approximately 0.5 miles (790 m) at its widest, while the smaller is about 0.15 miles (220 m) in size.

This encounter primarily served as an in-flight test of the spacecraft, specifically focusing on testing the system that allows Lucy to autonomously track an asteroid as it flies past at 10,000 mph, referred to as the terminal tracking system.

“This is an awesome series of images. They indicate that the terminal tracking system worked as intended, even when the universe presented us with a more difficult target than we expected,” said Tom Kennedy, guidance and navigation engineer at Lockheed Martin in Littleton, Colorado. “It’s one thing to simulate, test, and practice. It’s another thing entirely to see it actually happen.”

While this encounter was carried out as an engineering test, the team’s scientists are excitedly poring over the data to glean insights into the nature of small asteroids.

“We knew this was going to be the smallest main belt asteroid ever seen up close,” said Keith Noll, Lucy project scientist from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “The fact that it is two makes it even more exciting. In some ways these asteroids look similar to the near-Earth asteroid binary Didymos and Dimorphos that DART saw, but there are some really interesting differences that we will be investigating.”

It will take up to a week for the team to downlink the remainder of the encounter data from the spacecraft. The team will use this data to evaluate the spacecraft’s behavior during the encounter and to prepare for the next close-up look at an asteroid, the main belt asteroid Donaldjohanson, in 2025. Lucy will then be well-prepared to encounter the mission’s main targets, the Jupiter Trojan asteroids, starting in 2027.

By Katherine Kretke
Southwest Research Institute, San Antonio

Media contact: Nancy N. Jones
NASA’s Goddard Space Flight Center, Greenbelt, Md.