A tiny moon orbiting an asteroid turned out to consist of two touching pieces. NASA's Lucy spacecraft found the object, named Selam, during its November 2023 flyby of Dinkinesh. A mission update on October 19 revisited the discovery.
The unexpected shape makes the pair useful for studying how small bodies assemble. Lucy's main targets are Jupiter's Trojan asteroids, but encounters on the way have already revealed structures that distant observations could not resolve.
Dinkinesh was added to the flight plan as a test of the spacecraft's systems. Close-up images revealed a companion, then showed that the companion itself was a contact binary. That term describes two lobes touching to form one body.
The mission team says it had never previously seen a contact-binary satellite orbiting another asteroid. The finding came before Lucy reached either of the Trojan swarms leading and trailing Jupiter.
A later encounter, with Donaldjohanson in April 2025, revealed another two-lobed body. Researchers described a smooth neck joining its lobes and a complicated rotational motion.
These observations also serve an engineering purpose. Lucy used the flybys to test navigation and instruments before its main encounters. Its first Trojan encounter, with Eurybates and its moon Queta, is scheduled for August 2027.
The 12-year mission plans visits to 11 asteroids. That schedule is a mission plan, not a count of completed encounters.
The supposedly preliminary stops have already produced discoveries of their own.
