Asteroid's ancient water
NASA's Lucy mission reveals ancient water on asteroid Donaldjohanson from a past collision.
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Key Points
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Lucy measured Donaldjohanson’s non-standard dynamics in detail: it completes a full end-over-end rotation every 10.5 Earth days and also oscillates around its long axis every 26.5 days—supporting the “wobbling top” interpretation rather than simple single-axis rotation.
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The study reports a specific observational signature of resurfacing: craters smaller than about 0.4 kilometers in diameter appear to have been preferentially erased, which Marchi and colleagues attribute to seismic shaking after a more recent impact.
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Donaldjohanson’s size was given in one account as roughly 8 kilometers long and 3.5 kilometers wide, helping frame how Lucy’s short encounter could resolve lobes, neck structure, and mineralogical clues at high precision.
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Lucy’s closest flyby details were reported as April 20, 2025 at roughly 650 miles from the asteroid (and the mission used the encounter as rehearsal for the next Trojan target, beginning with Eurybates in 2027).
NASA's Lucy spacecraft has revealed that asteroid Donaldjohanson harbors signs of ancient liquid water — a finding that could reshape how scientists think about water delivery to early Earth. The discovery comes from Lucy's April 20, 2025 flyby, when the probe passed just 600 miles from the peanut-shaped rock, according to Space.com.
The results, published June 18, 2026 in the journal Science, show that the 8-kilometer-long asteroid is no ordinary space rock. Lead author Dr. Simone Marchi of the Southwest Research Institute called the encounter a window into the solar system's past, saying it gave scientists "a detailed understanding of its formation and evolution... including the ancient presence of water," as reported by IFLScience.
A Peanut-Shaped Time Capsule Born From Catastrophe
Donaldjohanson — nicknamed "DJ" — measures roughly 8 km long and 3.5 km wide. It has two cratered lobes joined by a smoother neck, giving it the look of a peanut shell. Space.com reports that scientists now believe it formed when two fragments from a massive collision gently merged together, creating what is called a contact binary.
That original collision happened about 155 million years ago. A roughly 50-mile-wide parent body was shattered when a 12-mile-wide projectile struck it, according to Gizmodo. This event created the Erigone asteroid family — a cluster of around 1,800 to 2,000 rocks that share similar orbits. DJ is one of its members.
Minerals Hint at Liquid Water in the Ancient Solar System
Perhaps the most striking find is chemical. Lucy's instruments detected iron-bearing phyllosilicates on Donaldjohanson's surface. These minerals only form when liquid water is present, according to Newsy Today. That means DJ's parent body was once water-rich — a surprise for a rock sitting in the inner asteroid belt, which scientists long assumed was dry.
The find supports the idea that water-bearing materials spread widely through the early solar system. It suggests that asteroids like Donaldjohanson may have helped deliver water — and possibly ingredients for life — to young planets like Earth. Head Topics notes that scientists see DJ as a potential clue to how this volatile delivery worked.
DJ's Wobbling Spin Puzzles Orbital Scientists
DJ does not spin the way most asteroids do. Instead of a clean single-axis rotation, it tumbles in two overlapping motions. It completes one end-over-end rotation every 10.5 Earth days. It also oscillates around its long axis every 26.5 days. Together, this creates a slow, wobbling motion — like a spinning top that has started to tip, according to Space.com.
Dr. Marchi says this wobble was likely triggered by the YORP effect — tiny forces from sunlight heating the asteroid's surface unevenly — over the last 20 to 60 million years. Mission principal investigator Dr. Hal Levison noted that while the flyby was meant as an engineering rehearsal, the asteroid's "strikingly complicated geology" produced unexpected scientific rewards, as reported by Newsy Today.
Missing Craters Point to Seismic Shaking After Recent Impacts
Scientists noticed something odd about DJ's surface: small craters are mostly gone. Features smaller than 0.4 km across appear to have been wiped clean. Researchers believe a more recent impact sent shockwaves through the asteroid's loose, rubble-pile interior. That shaking caused dust and rocks to shift, filling in and erasing the smallest craters, according to Gizmodo.
This finding matters beyond DJ. It changes how scientists estimate the ages of other small asteroids using crater counts. If seismic shaking can erase craters, those age estimates could be wrong. Lucy is now headed toward its primary targets — Jupiter's Trojan asteroids — with its first visit to Eurybates scheduled for August 12, 2027, according to Space.com.
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