In a thrilling milestone for planetary science, NASA’s Lucy spacecraft has successfully imaged asteroid Donaldjohanson, revealing intricate geological features and a surprising shape during its second asteroid flyby. The close encounter, which occurred on April 20, 2025, saw Lucy pass just 600 miles (960 km) from the asteroid, capturing detailed observations that may unlock secrets of our solar system’s ancient past.
A Unique Encounter with Donaldjohanson
Named after the paleoanthropologist who discovered the famous Lucy hominin fossil, Donaldjohanson is a relatively small but scientifically intriguing asteroid. The object lies within the main asteroid belt between Mars and Jupiter and is estimated to have formed about 150 million years ago — making it a valuable relic from the early solar system.
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As part of its mission progression, Lucy approached the asteroid at high speed, collecting data using its suite of instruments. The Long-Range Reconnaissance Imager (L’LORRI) aboard Lucy recorded images every two seconds during the flyby. The closest images, taken from 660 miles (1,100 km) away — just seconds before the point of closest approach — show intricate surface structures and hint at a contact binary shape: two lobes fused by a narrow, neck-like structure.
Striking Shape: A Nested Ice Cream Cone?
Early analysis suggests the asteroid’s form resembles two nested ice cream cones, an unexpected geometry that has fascinated the mission’s scientists. Hal Levison, Lucy’s principal investigator at the Southwest Research Institute (SwRI), explained the implications of this configuration.
“Asteroid Donaldjohanson has strikingly complicated geology,” said Levison. “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.”
The shape supports earlier ground-based observations of brightness fluctuations over a 10-day period, which hinted at an elongated body. However, the distinct narrow neck connecting the asteroid’s lobes adds a new layer of mystery. Is this the result of a gentle merger between two objects? Or erosion from billions of years in space?
Bigger Than Expected
One of the early surprises from the flyby is that Donaldjohanson is larger than previously estimated. New data suggest a length of 5 miles (8 kilometers) and a width of 2 miles (3.5 kilometers) at its widest point. Because the asteroid is larger than the L’LORRI imager’s field of view, the full shape is not yet fully resolved. Additional data, still being downlinked from the spacecraft, will provide a more comprehensive 3D model over the coming weeks.
A “Dress Rehearsal” for Bigger Targets
While Donaldjohanson was not a primary science target, the flyby was far from insignificant. According to NASA, the encounter served as a “full dress rehearsal” for future, more critical encounters with Jupiter Trojan asteroids — Lucy’s main targets.
“This encounter was a chance for us to execute our observation plan under real conditions,” said Levison. “Everything from the flyby timing to data acquisition was tested — and it went incredibly well.”
Lucy’s first asteroid encounter, with the small asteroid Dinkinesh in November 2023, was primarily a systems test. In contrast, the Donaldjohanson flyby pushed the mission team to simulate high-pressure scientific operations in preparation for future flybys, starting with Eurybates, a Jupiter Trojan, in August 2027.
Multi-Instrument Science Bonanza
Lucy carries an impressive array of scientific instruments that gathered diverse data during the Donaldjohanson flyby. These include:
- L’LORRI (Long-Range Reconnaissance Imager) – captured high-resolution images of the asteroid’s surface.
- L’Ralph – a color imager and infrared spectrometer designed to analyze surface composition.
- L’TES (Thermal Emission Spectrometer) – used to measure surface temperatures and thermal properties.
The full dataset from L’Ralph and L’TES will take weeks to downlink and process. Scientists hope to use this multi-dimensional data to determine Donaldjohanson’s mineral content, surface temperature gradients, and potential signs of past impacts.
The Broader Significance of Donaldjohanson
Although not a Trojan asteroid, Donaldjohanson offers a unique opportunity to deepen our understanding of how asteroids evolve in the main belt and how early solar system processes shaped them. NASA scientist Tom Statler emphasized the broader implications:
“These early images of Donaldjohanson are again showing the tremendous capabilities of the Lucy spacecraft as an engine of discovery,” he said. “The potential to really open a new window into the history of our solar system when Lucy gets to the Trojan asteroids is immense.”
From Fossils to the Stars
The asteroid’s namesake, Donald Johanson, famously discovered the 3.2-million-year-old hominin fossil Australopithecus afarensis, known as “Lucy,” in Ethiopia in 1974. By naming the spacecraft and now the asteroid after this significant discovery, NASA highlights the interdisciplinary value of exploration — linking planetary science with anthropology in a symbolic bridge across disciplines.
What’s Next for Lucy?
Now on its trajectory through the main asteroid belt, Lucy is continuing its nearly 12-year journey to explore the Jupiter Trojans, a group of asteroids that orbit the Sun along the same path as Jupiter. These asteroids are considered to be among the most pristine remnants of the primordial solar system.
Lucy’s targets include:
- Eurybates (August 2027)
- Polymele, Leucus, and Orus (2028–2033)
- Patroclus and Menoetius, a binary Trojan asteroid pair (2033)
Each of these encounters will offer unprecedented insight into how planetary building blocks were distributed and shaped during the solar system’s chaotic infancy.
Teamwork Behind the Scenes
The Lucy mission is a product of a wide collaboration:
- NASA’s Goddard Space Flight Center (Greenbelt, MD) oversees mission management and built the L’Ralph instrument.
- Southwest Research Institute (SwRI) leads the science team, planning, and data processing.
- Lockheed Martin Space (Littleton, CO) built the spacecraft and handles flight operations.
- KinetX Aerospace provides navigation, while the Johns Hopkins Applied Physics Laboratory (APL) designed and built L’LORRI.
- Arizona State University built the L’TES instrument.
- Lucy is part of NASA’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama.
A Glimpse Into Deep Time
NASA’s Lucy mission is living up to its namesake — providing insight into our origins, not through ancient bones, but through ancient rocks floating in space. With each flyby, Lucy’s instruments gather valuable clues to unlock mysteries that are billions of years old, offering humanity a deeper understanding of how the planets — and ultimately life — came to be.
