Lucy In Action: First Images Of Asteroid Donaldjohanson Promise New Discoveries

NASA’s Lucy spacecraft has received the first images of a small asteroid in the Donaldjohanson belt. In almost two months, Lucy will pass within 960 kilometres of this celestial wanderer, which has a width of about 4 kilometres. This will be the second asteroid encounter for the Lucy spacecraft. The resulting images provide insight into the mysterious nature of the asteroid, which will help study ancient Trojan asteroids.

First Images of the Next Target for Lucy

NASA recently released the first images of an object in the sights of the space agency’s research mission.

The two images, which were taken with Lucy’s Long Range Reconnaissance Imager (or L’LORRI for short), show the asteroid as a faint smudge.

Of course, it’s a far cry from the breathtaking astrophotographs. However, scientists are very encouraged by the result, as the optics captured the asteroid 70 million kilometres away from Lucy.

This Asteroid is a secondary target of NASA’s Lucy mission, which aims to study asteroids as “fossils” of planet formation. Lucy will fly by the asteroid on April 20, 2025, passing within 960 km. This encounter serves as a practice run for Lucy’s primary targets, the Jupiter Trojan asteroids.

Donaldjohanson: What Is Known About?

Asteroid Donaldjohanson, formally designated 52246 Donaldjohanson, is a carbonaceous C-type asteroid located in the inner main asteroid belt. It measures approximately 4 km in diameter and was discovered on March 2, 1981, by astronomer Schelte Bus at the Siding Spring Observatory in Australia.

Named after paleoanthropologist Donaldjohanson, who discovered the famous “Lucy” hominid fossil, this asteroid is part of the Erigone family, a group of carbonaceous asteroids formed approximately 130 million years ago. 

Donaldjohanson orbits the Sun every 3 years and 8 months at a distance of 1.9–2.8 AU with an eccentricity of 0.19 and an inclination of about 4°. The asteroid is notable for its slow rotation period of approximately 252 hours and a high lightcurve amplitude, suggesting it may be highly elongated or a binary system. NASA’s NEOWISE mission determined its surface albedo of 0.103.

This asteroid is symbolically significant for the Lucy mission, which explores Trojan asteroids and is also of great interest to scientific research.

As a member of the C-type asteroids, it is rich in organic compounds and water, making it valuable for studying the early stages of solar system formation.

In addition, Donaldjohanson’s size and shape may provide information about the processes that formed asteroids in the main belt, and its orbit will allow us to study its dynamics and interactions with other objects in the main belt.

At the same time, Donaldjohanson serves only as a test object for the Lucy mission, allowing it to test systems and prepare for its primary targets, the Trojan asteroids.

Trojan Asteroids: Mysterious Celestial Heroes

Trojan asteroids are groups of asteroids in the vicinity of the Lagrangian points L₄ and L₅ of planets such as Jupiter, Mars, Neptune, and Uranus. These points provide a stable position where the gravity of the planet and the Sun balance each other, allowing asteroids to remain there for long periods.

These objects are usually named after characters from the Trojan War described in the Iliad.

Their composition is similar to that of the Martian moons Phobos and Deimos, which include a mixture of ice and rocky debris.

Most of the Trojan asteroids (over 10,000) are located in the orbit of Jupiter.

They orbit as two “swarms” that lead and follow Jupiter in its orbit around the Sun and are thought to be comparable in number to objects in the main asteroid belt between Mars and Jupiter’s orbits.

Lucy: The First Mission to Explore Jupiter’s Trojan Asteroids

“Lucy” is the first space science mission to explore Jupiter’s Trojan asteroids.

The mission is named after the fossilised skeleton of a human ancestor, which was named after The Beatles’ song “Lucy in the Sky with Diamonds.”

“Lucy” launched in October 2021. In 2023, the mission observed the asteroid Dinkinesh and its tiny companion.

The spacecraft circled Earth late last year in preparation for a mission to Donaldjohanson. Earth’s gravitational assistance increased Lucy’s speed relative to the Sun by more than 25,750 kilometres per hour.

During its 12-year mission, “Lucy” will explore a record number of asteroids: it will fly past three in the asteroid belt, which orbits the Sun between the orbits of Mars and Jupiter, and then past eight Trojans, including five asteroids and satellites of three of them. “Lucy” will also fly past Earth three times to get a boost from its gravity, making it the first spacecraft to return to Earth’s neighbourhood from outside the solar system.

The first Trojan asteroid on Lucy’s watch list is Eurybat, much larger than Donaldjohanson – about 64 kilometres across. The flyby of Eurybat will help researchers understand how the Trojan asteroids ended up mostly together in front of Jupiter in their orbit around the Sun and why they have such a composition.