Overview

Asteroid Donaldjohanson is a uniquely shaped fragment of an asteroid that formed about 150 million years ago. It is located in the main asteroid belt between Mars and Jupiter. NASA’s Lucy spacecraft obtained a close look at Donaldjohanson as flew by on April 20, 2025, on its way to explore the Jupiter Trojan asteroids. The spacecraft came approximately 600 miles (960 km) from the asteroid.

The asteroid was previously observed to have large brightness variations over a 10-day period, so some of Lucy team members’ expectations were confirmed when the first images showed what appeared to be an elongated contact binary (an object formed when two smaller bodies collide). However, the team was surprised by the odd shape of the narrow neck connecting the two lobes, which looks like two nested ice cream cones.

Asteroid Donaldjohanson has strikingly complicated geology,” says Hal Levison, principal investigator for Lucy at Southwest Research Institute, Boulder, Colorado. “As we study the complex structures in detail, they will reveal important information about the building blocks and collisional processes that formed the planets in our Solar System.”

From a preliminary analysis of the first available images collected by the spacecraft's L’LORRI imager, the asteroid appears to be larger than originally estimated, about 5 miles (8 km) long and 2 miles (3.5 km) wide at the widest point. In this first set of high-resolution images returned from the spacecraft, the full asteroid is not visible as the asteroid is larger than the imager’s field of view. It will take up to a week for the team to downlink the remainder of the encounter data from the spacecraft; this dataset will give a more complete picture of the asteroid’s overall shape.

Like Lucy’s first asteroid flyby target, Dinkinesh, Donaldjohanson is not a primary science target of the Lucy mission. The Lucy spacecraft will spend most of the remainder of 2025 travelling through the main asteroid belt. Lucy will encounter the mission’s first main target, the Jupiter Trojan asteroid Eurybates, in August 2027.

“These early images of Donaldjohanson are again showing the tremendous capabilities of the Lucy spacecraft as an engine of discovery,” said Tom Statler, program scientist for the Lucy mission at NASA Headquarters in Washington. “The potential to really open a new window into the history of our solar system when Lucy gets to the Trojan asteroids is immense.”

How the Asteroid Got Its Name

Asteroid Donaldjohanson is named for anthropologist Donald Johanson, who discovered the fossilized skeleton — called “Lucy” — of a human ancestor. NASA’s Lucy mission is named for the fossil.