There is a small object in the main asteroid belt, between Mars and Jupiter, that rotates like a wobbly top. It takes ten and a half days to turn end-over-end, and another twenty-six and a half to wobble back and forth around its long axis, as if unsure of its balance. It is shaped like a peanut — two lobes joined by a narrow neck, the kind of shape a child might draw if asked to imagine a lumpy asteroid. It is about eight kilometers long. It is called Donaldjohanson.
It is named after the paleontologist who, in 1974, discovered a partial skeleton of an early human ancestor in the Afar Triangle of Ethiopia. He named her Lucy, after the Beatles song playing on a cassette tape in the camp that night. Three million years old, small, bipedal — one of the oldest hominids ever found. The fossil that rewrote part of our origin story.
And the spacecraft that visited the asteroid last April is called Lucy.
I keep returning to this recursion. A fossil names a spacecraft. The spacecraft visits a rock named after the man who found the fossil. Both are looking for origins — Lucy the fossil taught us where we came from; Lucy the probe is built to understand where the solar system came from. The asteroid is a dress rehearsal, a practice target, before the real mission begins: the Trojan asteroids, two swarms of ancient rocks that lead and trail Jupiter in its orbit, preserved since the early days of the solar system like specimens in a drawer.
What Lucy found, and what researchers reported in Science last week, is that Donaldjohanson has lived a more complicated life than its modest size suggests. It formed 155 million years ago from the rubble of a collision — not ancient in geological terms, almost young. Two fragments, knocked loose from a larger carbon-rich body, drifted back together and settled into each other’s gravity. But the story did not end there.
The Sun has been slowly reshaping it ever since.
There is an effect called YORP — Yarkovsky-O’Keefe-Radzievskii-Paddack, if you want the full liturgy — and it is as gentle as things get in physics. Sunlight warms the asteroid’s surface. The surface radiates that heat away as infrared light. Because the asteroid is not a perfect sphere, the radiation imparts a tiny, uneven recoil, like a very slow rocket thruster. Over millions of years, this has slowed Donaldjohanson’s spin from a rotation of once per hour to its current stately tumble. Loose material has slid down slopes. Craters have worn soft. The peanut has been polished by light.
And then there is the water.
Lucy’s instruments detected iron-rich clay minerals on the surface — clays that need liquid water to form. But the iron has not been replaced by magnesium, which is what happens when water lingers for millions of years. On asteroids Bennu and Ryugu, both visited by sample-return missions, the magnesium clays suggest prolonged soaking, perhaps inside larger parent bodies that broke apart billions of years ago. Donaldjohanson’s iron clays tell a different story: water was there, but briefly. A fleeting presence. A touch and then a withdrawal.
I do not know why this moves me. Perhaps it is the thought of water, that substance we search for on every world, leaving only a chemical signature on a rock that has been dead for a hundred and fifty million years. Perhaps it is the image of the asteroid, wobbling alone in the dark, slowly forgetting the collision that made it, the water that touched it, everything except the patient torque of sunlight. Objects in space have no memory, but they keep records. The clays are a record. The worn craters are a record. The wobble itself is a record — of a shape that is not symmetric, that radiates heat unevenly, that has been pushed and pulled by the nearest star for longer than mammals have existed.
The Lucy mission will reach its first Trojan asteroid in August 2027. The Trojans are different — older, more primitive, perhaps unchanged since the solar system’s formation. Scientists expect to be surprised. “Our understanding of solar system formation is destined to be challenged,” said Simone Marchi, the mission’s deputy principal investigator. That is science’s way of saying: we are about to discover that what we knew was incomplete.
But I keep thinking about the names. Donald Johanson, now in his eighties, has lived to see his name attached to a wobbling peanut in the asteroid belt, visited by a spacecraft named after the fossil he found. The fossil was named after a song. The song was named after a girl. The girl was imaginary, a painting by a child. The chain of associations is so long and so fragile — a child’s drawing, a Beatles lyric, a skeleton in Ethiopian dust, a spacecraft, a rock between Mars and Jupiter — and yet it holds together. It is one of the longest sentences humanity has ever written, and we are still in the middle of it.
The asteroid wobbles. The spacecraft flies on. The Sun continues its slow work of reshaping what we thought was permanent. And somewhere, in a drawer or a database or the memory of an old man, a small hominid skeleton waits, still teaching us where we came from, still sending us outward to look for more.