NASA Encounters Wobbling, Peanut-Shaped Asteroid With A Prehistoric Secret

NASA’s Lucy Probe Reveals a Lopsided, Wobbling Asteroid Born From One of the Solar System’s Most Violent Crashes

Deep in the asteroid belt, there’s a space rock doing something genuinely strange: it’s not just spinning, it’s wobbling. NASA’s Lucy spacecraft recently flew past an asteroid called Donaldjohanson, and what scientists found has reshaped what they know about how these ancient objects behave, age, and change over time.

On April 20, 2025, Lucy zipped past the asteroid, nicknamed “DJ” by the research team, closing to within about 961 kilometers while traveling at roughly 13 kilometers per second. The close encounter revealed a lumpy, peanut-shaped rock stretching nearly 9 kilometers at its longest point, slowly tumbling through space in a way that defies the simple spinning motion most people picture when they think of a rotating asteroid. The findings, published in the journal Science, offer a remarkably detailed portrait of a rock that has been quietly evolving for over a hundred million years.

DJ isn’t just any asteroid. Scientists believe it’s a fragment of a much larger parent body, estimated at around 80 kilometers across, smashed apart by a roughly 20-kilometer impactor about 155 million years ago. That’s around the same time dinosaurs were still roaming Earth. Its chemical fingerprint, including iron-bearing minerals associated with liquid water, supports a connection to that long-destroyed parent body.

DJ’s Peanut Shape Tells the Story of a Violent Creation

DJ’s most immediately visible feature is its shape: two distinct, heavily cratered lobes, like two rough boulders pressed together, connected by a smoother, bridge-like middle section. Overall, it measures 8.8 kilometers long, 4.4 kilometers wide, and 3.1 kilometers tall. Lucy only captured the inbound side during the flyby, with observations cut off 31 seconds before closest approach, so the far side was modeled rather than directly imaged. Researchers believe this double-lobed structure formed after the original collision shattered the parent body, with fragments slowly clumping back together under their own gravity.

That middle section is noticeably smoother than the rest of the surface. Researchers propose that earlier in DJ’s history, as sunlight-driven effects slowed its spin, the asteroid reached a roughly 10-hour rotation period. At that point, slopes in the neck region may have failed, sending loose material toward both lobes, building the ridge and leaving the neck smoother than the cratered lobes.

How Donaldjohanson’s Wobbling Rotation Defies Expectations

One of the most surprising findings is how DJ rotates. Rather than spinning cleanly around a fixed axis the way a top does, DJ tumbles. Its rotation is unstable, creating a slow, gyrating motion inferred from brightness changes over time. Researchers detected this by studying how DJ’s brightness varied over the 59 days before the flyby. Those variations revealed two overlapping cycles, one roughly every 10.5 days and another every 19 days. That dual rhythm is the telltale sign of a tumbling rotation.

What makes this especially interesting is that DJ is expected to stay in this tumbling state for an extraordinarily long time. Scientists calculated that it would take approximately 20 billion years, far longer than the current age of the universe, for DJ to naturally settle back into a clean, stable spin on its own, though that figure is model-based and tied to assumptions about DJ’s internal properties. Based on similar modeling, the tumbling likely began somewhere between 80 and 120 million years after the original collision, as the slow, steady pressure of sunlight gradually braked its spin.

Craters Reveal a Surface Reshaped in the Last 40 Million Years

Craters larger than about 0.4 kilometers are abundant and consistent with DJ’s age, but smaller craters are surprisingly sparse, far fewer than scientists would expect if the surface had simply been accumulating impacts undisturbed since the original collision. Researchers concluded those smaller craters were likely wiped out sometime in the last 40 million years, probably by shaking triggered by a larger impact. When a big enough rock slams into an asteroid, the resulting shockwaves can cause loose surface material to shift and settle, filling in and erasing smaller craters. More localized crater degradation on the middle section is estimated within the last 20 million years, though these timescales carry uncertainties tied to assumptions about impact rates. Researchers also confirmed that DJ has no moons and showed no signs of cometary activity.

Ancient Water Locked in DJ’s Chemistry Points to Solar System Origins

Lucy carried instruments capable of measuring the chemical makeup of DJ’s surface from a distance, and the results are consistent with a history involving liquid water, not on DJ itself, but inside the larger parent body before it was destroyed. DJ’s chemistry suggests this process was cut short at an early stage, possibly because the parent body ran out of water or heat. This sets DJ apart from well-studied asteroids like Bennu and Ryugu, which show signs of more extensive water alteration.

Lucy’s main mission is to study the Trojan asteroids, space rocks that share Jupiter’s orbit. But the detour past DJ has proven scientifically rich, delivering a close-up look at an asteroid whose entire life story, from the catastrophic smash-up that created it to the ancient water that once flowed inside its parent body, can now be read in its craters, chemistry, and wobbling spin.

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