Somewhere between Mars and Jupiter, a three-mile-wide rock drifts through space, carrying secrets from an ancient planetary collision. Its name? (52246) Donaldjohanson. And when NASA’s Lucy spacecraft swings by in April 2025, we’ll finally get a close look at this mysterious wanderer.
Donaldjohanson didn’t start as a lone traveler. Scientists at the Southwest Research Institute (SwRI) believe it was born about 150 million years ago when a much larger asteroid shattered into pieces. Since then, time and physics have played their usual tricks, sculpting its orbit and spin into something unique.
“Based on ground-based observations, Donaldjohanson appears to be a peculiar object,” says Dr. Simone Marchi, deputy principal investigator for the Lucy mission. That’s scientist-speak for “this rock is a little strange.” And strange it is—potentially elongated, spinning unusually slowly, and possibly influenced by thermal torques that have been messing with its rotation for eons.
Donaldjohanson isn’t just any space rock; it’s part of the Erigone collisional asteroid family, a group of fragments that share a common origin. Its ancestral asteroid exploded in the inner main belt, not far from the regions that spawned near-Earth asteroids Bennu and Ryugu. Those names should ring a bell—Bennu was recently sampled by NASA’s OSIRIS-REx, and Ryugu by Japan’s Hayabusa2.
Marchi is eager for Lucy’s flyby, noting that Donaldjohanson seems vastly different from those two well-studied asteroids. “Yet, we may uncover unexpected connections,” he teases. Translation: Space loves surprises, and there’s no telling what secrets this asteroid might spill.
Its name, however, is no mystery. Donaldjohanson is named after the paleontologist who discovered Lucy, the famous 3.2-million-year-old hominin fossil found in Ethiopia in 1974. That fossil rewrote the story of human origins. Now, the Lucy mission hopes to do something similar—except this time, it’s rewriting the history of the solar system.
This rock also holds another weird distinction: It’s the only named asteroid to be visited while its human namesake is still alive. If that’s not sci-fi enough for you, imagine this—an ancient asteroid, a spacecraft named after an early ancestor, and a mission spanning over a decade, all connected by a single name.
Lucy, the spacecraft, is on a 12-year odyssey to visit 11 asteroids, primarily the Trojan asteroids that lurk in Jupiter’s orbit. Before it reaches those fossilized planetary leftovers, though, it will swing by Donaldjohanson—a sort of cosmic test run. “Encounters with main belt asteroids not only provide a close-up view of those bodies,” says Dr. Hal Levison, Lucy’s principal investigator, “but also allow us to perform engineering tests of the spacecraft’s innovative navigation system before the main event.”
Think of it as a dress rehearsal before Lucy dives into the real fossil record of the solar system. These space rocks are time capsules from an era before planets were fully formed, holding the raw materials that built everything from Earth to Jupiter. If you want to understand where we came from, you start with the relics drifting in space.
April 2025 can’t come soon enough.
Did You Know?
- Asteroids can have moons. Some even have rings—because apparently, space rocks like to accessorize.
- Donaldjohanson rotates so slowly that if you stood on it (ignoring the whole “no atmosphere” thing), you’d barely notice it spinning beneath you.
- NASA’s Lucy spacecraft is powered by some of the largest solar panels ever sent beyond Mars—because space isn’t just cold, it’s also stingy with sunlight.
