Most asteroids, from a great distance, look more or less like potatoes — irregular, lumpy, and unremarkable. Donaldjohanson looked like a peanut. And it was wobbling.
Data returned from NASA's Lucy spacecraft, which buzzed the 5-mile-wide asteroid on April 20, 2025, at a blistering 30,000 mph, has now been analyzed and published in the journal Science as of June 18, 2026. The results paint a portrait of a body unlike any asteroid humans have sampled or studied up close: a bilobate structure — two distinct lobes connected by a narrow neck — that is tumbling end-over-end every 10.5 Earth days while simultaneously wobbling around its long axis once every 26.5 days. It is, in the driest possible scientific terms, in a state of non-principal-axis rotation. In less dry terms, it is doing something deeply strange for a rock that has been floating in space for 155 million years.
A Dress Rehearsal That Upstaged the Main Act
Donaldjohanson was never supposed to be the star of the Lucy mission. It was a warm-up — a "dress rehearsal" encounter on the spacecraft's long journey to Jupiter's Trojan asteroids, those ancient swarms of space rocks that share the gas giant's orbit around the Sun. Lucy's primary targets don't come into play until it reaches Eurybates on August 12, 2027. But the dress rehearsal turned out to be far more interesting than anyone anticipated.
Lucy's L'LORRI instrument — the Lucy Long Range Reconnaissance Imager, a high-resolution black-and-white camera — began collecting images from an initial distance of 58,000 miles, gathering data over a two-hour approach window that culminated in a closest pass of just 650 miles (about 1,000 kilometers). That's close enough to resolve surface features: craters, ridges, and the unmistakable pinched waist where the asteroid's two lobes meet.
What emerged from the images was a body that didn't behave the way models predicted a small main-belt asteroid should. The dual rotation — end-over-end plus a lateral wobble — immediately raised questions about how Donaldjohanson formed and what forces have been acting on it since.
Born From Wreckage
The research team's analysis points to a violent origin story. Donaldjohanson appears to be roughly 155 million years old, formed when a larger, carbon- and water-rich asteroid was shattered by a catastrophic collision. The fragments from that impact didn't simply scatter into the void. Some of them drifted back together under their own feeble gravity, slowly coalescing into the bilobate structure we see today — two major chunks that stuck together at a narrow contact point, producing the peanut shape.
This kind of formation mechanism, called a rubble-pile reaccumulation, isn't unique. The near-Earth asteroids Bennu and Ryugu — targets of NASA's OSIRIS-REx and Japan's Hayabusa2 missions, respectively — are also rubble piles. But the comparison between Donaldjohanson and its better-known cousins is where things get genuinely illuminating.
Three Rubble Piles, Three Very Different Stories
Bennu and Ryugu are both between 1 and 2 billion years old. They formed deep in the asteroid belt and, over geological time, migrated inward to near-Earth orbits where solar radiation, gravitational nudges, and other forces reshaped their surfaces and sped up their rotations. Bennu spins once every four hours. Ryugu completes a rotation every seven hours. Both show evidence of prolonged exposure to liquid water early in their histories — their surfaces are rich in magnesium-bearing clay minerals that form only through extended contact with water.
Donaldjohanson breaks the pattern on nearly every count. At 155 million years old, it is dramatically younger. It never migrated — it has remained in the main asteroid belt since the day it formed. And while Lucy's infrared spectrometer detected iron-rich clay minerals on its surface, confirming that liquid water was present at some point in the history of Donaldjohanson's parent body, magnesium-rich clays were conspicuously absent. The implication: whatever water exposure Donaldjohanson's source material experienced, it was brief. This was a quick splash, not a long soak.
The rotation comparison is equally stark. Bennu and Ryugu are compact, fast-spinning tops. Donaldjohanson is an elongated, slowly tumbling peanut. But it wasn't always slow. The research team estimates that when Donaldjohanson first formed, it was spinning at least ten times faster than its current rate. Something has been bleeding away its angular momentum for tens of millions of years.
Death by Sunlight
The culprit, according to the team's analysis, is the YORP effect — a phenomenon in which sunlight absorbed and re-emitted as heat by an irregularly shaped asteroid generates tiny recoil forces. On a perfectly spherical body, these forces cancel out. On something shaped like a peanut, they don't. Over millions of years, the asymmetric thermal radiation acts like an invisible brake (or accelerator, depending on the geometry), gradually altering the body's spin rate and axis.
For Donaldjohanson, the YORP effect has been working as a brake. The team estimates the slowdown has been ongoing for the last 20 to 60 million years, steadily draining the asteroid's rotational energy and pushing it into the complex, wobbling tumble that Lucy observed. It is a textbook case of how the seemingly negligible force of re-radiated sunlight can, given enough time, fundamentally reshape the dynamics of a small body in space.
What Comes Next
Lucy is now continuing its journey outward. Its next encounter — and the real beginning of its primary science mission — is the Trojan asteroid Eurybates, scheduled for August 12, 2027. The Trojans are a fundamentally different population from main-belt asteroids like Donaldjohanson. Trapped in Jupiter's gravitational sweet spots for billions of years, they are thought to be among the most pristine relics of the early solar system, preserved in a kind of gravitational deep freeze since the era when the giant planets were still migrating to their current orbits.
As Simone Marchi, Lucy's deputy principal investigator at the Southwest Research Institute, put it: "It's helpful for scientists to compare Donaldjohanson with asteroids like Bennu and Ryugu, because every subtle difference is another clue to our origin story."
If a dress rehearsal flyby of a relatively young main-belt asteroid can upend expectations this thoroughly, the Trojans — billions of years older and far less studied — may have considerably larger surprises in store.
Why It Matters
Donaldjohanson is the kind of result that recalibrates assumptions. Before this flyby, the prevailing understanding of small rubble-pile asteroids was largely built on Bennu and Ryugu — ancient, fast-spinning, water-altered bodies that had migrated far from their birthplaces. Donaldjohanson shows that a younger body, one that stayed put in the belt, can look and behave in fundamentally different ways: different shape, different rotation state, different water history, different evolutionary trajectory.
That matters because planetary scientists use asteroids as forensic evidence for reconstructing the early solar system. Every assumption about how these bodies form, evolve, and move has downstream consequences for models of planetary formation and migration. A single asteroid that breaks the mold forces a re-examination of which patterns are universal and which are artifacts of a biased sample — we've only visited a handful of these objects up close, and each new one has complicated the picture rather than confirming it.
Lucy's primary mission to the Trojans, now less than 14 months away from its first major encounter, promises to complicate it further. And that, in planetary science, is exactly the point.
