NASA’s Lucy spacecraft, on its way to Jupiter’s Trojan asteroids, has its next target in its sights: the main belt asteroid 52246 Donaldjohanson.
Currently 45 million miles (70 million kilometers) from the two-mile-wide (3.2-kilometer-wide) Donaldjohanson, Lucy‘s high-resolution camera L’LORRI (Lucy Long Range Reconnaissance Imager) spotted the asteroid moving against a background of stars. Lucy will continue to track Donaldjohanson, adjusting its trajectory to ensure an accurate flyby on April 20, when the spacecraft will come within 596 miles (960 kilometers) of the asteroid, which orbits in the asteroid belt between Mars and Jupiter.
The encounter with Donaldjohanson won’t be Lucy’s first visit to an asteroid. Having launched on Oct. 16, 2021, Lucy encountered the asteroid Dinkinesh and its moon, Selam, in November of 2023. Like Donaldjohanson, Dinkinesh and Selam are also inhabitants of the asteroid belt between Mars and Jupiter. Selam in particular was very interesting because it turned out to be a contact binary — two separate objects touching each other and held together by their mutual gravity. Selam’s origin is still a puzzle, but scientists think it might be made from material flung off Dinkinesh as Dinkinesh’s rotation was spun up by solar heating, exerting a torque over the course of millions of years.
Although relatively few minor planets have been explored by spacecraft, a high fraction of them have proved to be anything but boring, some having accompanying moons, others adopting unusual shapes and some spraying jets of debris.
For now, however, Donaldjohanson appears only as a point of light to Lucy, and the spacecraft won’t be able to detect any details about its structure until the day of the close encounter, when Donaldjohanson will appear large enough in Lucy’s sky to begin to resolve its features.
Who knows what Lucy will find?
Then, after the Donaldjohanson fly-by, Lucy will still have a packed schedule ahead of it. In August of 2027, Lucy will have its first encounter with one of Jupiter’s Trojan asteroids. The Trojans are two huge swarms of asteroids that have settled into the Lagrange L4 and L5 points, 60 degrees ahead and 60 degrees behind Jupiter in its orbit around the sun. The Trojan asteroids are all named after heroes of the Trojan War in Greek mythology — the first Trojan that Lucy will meet is the 620-mile-wide (1,000-kilometer-wide) 3548 Eurybates, in the “Greek camp” located at L4. After visiting three more Trojan asteroids in the Greek camp, Lucy will actually head back to Earth in 2030 to receive a gravitational slingshot towards the “Trojan camp” at Jupiter’s L5 point in 2033.
And, if you’re wondering, Donaldjohanson has a direct link to the Lucy spacecraft’s name. Donald Johanson is a paleoanthropologist who discovered parts of a fossilized skeleton of an ancestor of homo sapiens’, an australopithecine that lived 3.2 million years ago in what is now Ethiopia. That skeleton was named “Lucy.” The spacecraft named after that ancient hominid is also exploring fossils, in the sense that asteroids are leftovers from the dawn of the solar system and can tell us much about Earth’s origin, just as Lucy the fossil can tell us about human evolution.
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