NASA's Lucy Mission Reveals an Asteroid's Hidden History

NASA's Lucy spacecraft is traveling through space on a mission to study ancient asteroids near Jupiter. Along the way, it stopped to take a close look at a smaller asteroid called Donaldjohanson. Scientists just published what they learned from that visit — and the findings tell a rich story about how space rocks change over time.

Lucy launched in the fall of 2021, right in the middle of the COVID pandemic. Because of that, the launch didn't get much attention in the news. But the spacecraft has been quietly traveling through space ever since, on a six-year trip toward Jupiter. It is expected to arrive at its main targets in August 2027.

Those main targets are called Trojan asteroids. Trojans are space rocks that travel around the sun in two giant groups near Jupiter — one group ahead of the planet and one trailing behind. Scientists think the Trojans are like fossils from the early solar system, pushed into place long ago by powerful gravitational forces between the giant planets. Some researchers believe that early collisions involving these asteroids may have helped bring water and other building blocks of life to Earth.

On the way to the Trojans, Lucy tested its tools by visiting two smaller asteroids in the 'main belt,' the zone between Mars and Jupiter. The first was called Dinkinesh, visited in 2023. The second was Donaldjohanson, visited in 2025. Donaldjohanson is shaped like a peanut, tumbles slowly through space, and is about twice as long as New York City's Central Park. It was named after Donald Johanson, the scientist who discovered the famous 'Lucy' human ancestor fossils — which also inspired the spacecraft's name.

Now, a new study published in the journal Science shares what Lucy found during the Donaldjohanson flyby. The lead author is Simone Marchi, a scientist at the Southwest Research Institute and a key member of the Lucy team. He says this asteroid was not just a quick test stop — it was a chance to study a rock with a known history. Donaldjohanson is most likely a piece of a larger asteroid called Erigone, which broke apart about 150 million years ago after a massive collision.

'In terms of the solar system's history, that's practically yesterday,' Marchi said. That makes Donaldjohanson a useful 'anchor point' for scientists trying to understand how asteroids change over time. Because they know roughly when it formed, they can compare what they see now to what they'd expect after 150 million years of space weathering. That kind of known starting point is rare and valuable in asteroid science.

Lucy's measurements showed that Donaldjohanson is rich in carbon, just like other members of the Erigone asteroid family. The spacecraft also found minerals that had been changed by water — probably long before the Erigone parent body broke apart. Scientists were also able to count the craters on the asteroid's surface and sort them by size. Based on that count, they estimated the asteroid is about 155 million years old, which lines up well with the known age of the Erigone family.

The asteroid's peanut shape and slow tumble are likely caused by sunlight. Over millions of years, sunlight can push on a spinning asteroid just enough to slowly change how fast it spins. This gradual change can also move material around on the surface. Scientists believe that is what shaped Donaldjohanson into its current lopsided form. It's a slow and subtle process, but over millions of years, it adds up.

One especially curious finding involves the narrow 'neck' that connects Donaldjohanson's two lobes. That area has almost no small craters — ones less than about half a kilometer wide. Scientists think this is because landslides wiped them away as the asteroid's spin slowed down. There may also have been a separate impact about 40 million years ago that shook the whole asteroid and erased more craters. These clues helped scientists piece together a full timeline of the asteroid's life.

Marchi said the team is proud of the detailed picture they were able to build. 'We're not claiming we now understand everything, but what we know so far is a nice story that makes sense with our previous understanding,' he said. The results from Donaldjohanson also help scientists prepare for what they'll find when Lucy reaches the Trojans, which no spacecraft has ever visited. The methods Lucy used here — counting craters, measuring minerals, tracking shape — will all be used there too.

Lucy's next stop is a Trojan asteroid called Eurybates, which it will fly past on August 12, 2027. Eurybates is about 68 kilometers wide and travels with a smaller companion rock called Queta. After that, Lucy will visit three more Trojans before swinging back past Earth in 2031. Earth's gravity will then give Lucy a speed boost for one final destination — a binary asteroid in the trailing Trojan cloud, which the spacecraft is set to reach in 2033.