Five Years In, NASA's Lucy Is Less Than a Year From Its First Trojan Asteroid

CAPE CANAVERAL, Florida — Five years after launching on October 16, 2021, NASA's Lucy spacecraft is now less than a year away from the encounters it was built for: the first-ever close-up exploration of the Trojan asteroids that share Jupiter's orbit. Researchers from the Southwest Research Institute (SwRI), which leads Lucy's science team, marked the five-year milestone on October 19, 2026, noting that the spacecraft has already rewritten parts of the textbook on small bodies — before it has even reached its main targets, according to EarthSky and phys.org.

Illustration: A concept illustration of the Lucy spacecraft approaching Trojan asteroids near Jupiter.

What Happened

Lucy launched on October 16, 2021, on a 12-year mission to visit 11 asteroids: three in the main asteroid belt between Mars and Jupiter, and eight Trojan asteroids that travel in two swarms ahead of and behind Jupiter in its orbit. The Trojans, named after characters from Homer's Iliad, are considered fossils of planet formation — primitive bodies that have been trapped in Jupiter's orbit, 60 degrees ahead of and behind the giant planet, since the early solar system.

Five years in, Lucy has already visited three main-belt asteroids, using those flybys as both science opportunities and dress rehearsals for the Trojan encounters. Its first Trojan flyby is now on the calendar: Eurybates, along with its satellite Queta, on August 12, 2027, according to the Cosmic Herald and SwRI summaries published in October 2026. That will be the first close look any spacecraft has had at a member of this population.

"Lucy is an ambitious NASA mission," said principal investigator Hal Levison of SwRI. "As we passed through the main asteroid belt, we visited three asteroids, capturing close-up views of those bodies while performing engineering tests of the spacecraft's innovative navigation system in advance of the main event to study the Trojans. These relics are effectively fossils of the planet formation process, holding vital clues to deciphering the history of our solar system."

The mission has also had to overcome adversity. Shortly after launch, one of Lucy's two giant circular solar arrays failed to fully deploy. Engineers working from millions of miles away diagnosed the problem and devised procedures to get the array almost fully open, and it now functions as intended, according to phys.org.

Background

Lucy's main-belt encounters have already delivered genuine surprises. Its first target, the small asteroid Dinkinesh, turned out to have a moon — and that moonlet, now named Selam, is itself a contact binary, a single object made of two touching lobes. "Though contact binaries seem to be fairly common in the solar system, we haven't had the opportunity to see many up close," said SwRI's John Spencer, Lucy's deputy project scientist. "And we have never seen one orbiting another asteroid."

In April 2025, Lucy flew by its second main-belt target, Donaldjohanson, and found another contact binary — a peanut-shaped, two-lobed body connected by a remarkably smooth neck. "The Donaldjohanson flyby revealed many surprises about the small asteroid," said SwRI's Dr. Simone Marchi, the mission's deputy principal investigator. "The asteroid also wobbles, rotating end-over-end once every 10.5 Earth days while rolling around its lateral axis once every 26.5 days." Donaldjohanson was born about 155 million years ago, researchers believe, when a catastrophic collision shattered a much larger parent asteroid and two lobes of debris drifted together and stuck, bound only by their feeble gravity.

Lucy is the 13th mission in NASA's Discovery Program. NASA's Goddard Space Flight Center manages the mission, Lockheed Martin built the spacecraft, and SwRI's Boulder office hosts the principal investigator. The spacecraft is named for the famous Lucy hominin fossil found in Ethiopia in 1974, a fossil of a human ancestor — a nod to the mission's goal of uncovering fossils of planet formation.

The Trojan asteroids themselves have never been explored by any spacecraft. They are divided into two swarms: the Greek camp ahead of Jupiter and the Trojan camp trailing behind it. Because they have spent billions of years in the cold outer solar system, largely undisturbed, scientists believe they preserve material from the era when the giant planets were still forming and migrating.

Illustration: A concept illustration of asteroid Dinkinesh and its moon Selam.

Why It Matters

The Trojan encounters matter because they address one of the biggest open questions in planetary science: how the solar system assembled itself. The leading models suggest the giant planets did not form exactly where they are today, and that their migration scattered small bodies across the solar system. The Trojans, captured in Jupiter's gravitational Lagrange points, may be refugees from that chaotic era — some possibly born far beyond Jupiter, in the distant Kuiper Belt.

Studying their composition, density and surface features will let scientists test those models directly. Lucy's three instruments are designed for exactly that work: L'Ralph will probe chemical composition and search for tenuous atmospheres, L'LORRI will capture detailed surface images, and L'TES will measure surface temperature and thermal inertia, according to mission summaries.

The main-belt surprises also matter in their own right. Finding two contact binaries in a row — one of them orbiting another asteroid — suggests these odd, stuck-together bodies may be far more common than previously thought, and that collisions and gentle mergers have shaped small bodies throughout solar system history. As Marchi and colleagues have noted, Donaldjohanson's peanut shape tells a violent story of fragmentation and reassembly.

There is also an engineering legacy. Lucy's navigation system, tested during the main-belt flybys, must work flawlessly during the Trojan encounters, when the spacecraft will hurtle past its targets at high speed with only brief windows for imaging. The successful main-belt flybys, including the recovery from the solar-array deployment problem, give the team confidence heading into the main event.

Illustration: A concept illustration of the peanut-shaped asteroid Donaldjohanson.

What Happens Next

The primary scientific campaign begins in less than a year. After Eurybates and Queta on August 12, 2027, Lucy is scheduled to visit Polymele and its companion satellite on September 14, 2027, Leucus in April 2028 and Orus in November 2028. Following those flybys, Lucy will swing back toward Earth for a gravitational boost in December 2030, a trajectory that will carry it toward its final primary target, the binary Trojan system Patroclus and Menoetius, in March 2033.

Each encounter will be brief — a high-speed flyby with hours of close observation — but together they will build the first comparative portrait of a population of bodies no spacecraft has ever visited. Scientists will be comparing Trojans of different sizes, colors and compositions to determine whether they share a common origin or were captured from different parts of the early solar system.

For now, the Lucy team is preparing for the encounters while continuing to analyze data from the main-belt flybys. As EarthSky summarized the five-year milestone, Lucy is "now less than a year from reaching the Trojan asteroids near Jupiter" — and the discoveries it has already made suggest the main event may hold more surprises still.

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FAQ

What is NASA's Lucy mission?

Lucy is a NASA Discovery Program spacecraft launched on October 16, 2021, on a 12-year mission to visit 11 asteroids: three in the main asteroid belt and eight Trojan asteroids that share Jupiter's orbit. It is the first mission ever sent to explore the Trojans.

What are Trojan asteroids?

Trojan asteroids are two swarms of asteroids that travel in Jupiter's orbit, one group 60 degrees ahead of the planet and one trailing behind it. They are thought to be primitive remnants from the early solar system, trapped in Jupiter's gravitational Lagrange points.

When will Lucy reach its first Trojan asteroid?

Lucy is scheduled to fly past Eurybates and its satellite Queta on August 12, 2027. That will be the first close look any spacecraft has had at a Jupiter Trojan asteroid.

What has Lucy already discovered?

Lucy found that its first main-belt target, Dinkinesh, has a contact-binary moon named Selam, and that its second target, Donaldjohanson, is itself a peanut-shaped contact binary that wobbles as it rotates. Both findings were surprises.

How long will the Lucy mission last?

The mission is planned for 12 years, with Trojan flybys running from 2027 to 2028 and a final encounter with the binary Trojan system Patroclus and Menoetius in March 2033, after an Earth gravity assist in December 2030.

Sources

• EarthSky — "Lucy mission to Trojan asteroids: 5 years of discoveries" — October 2026
• phys.org — "Lucy mission marks 5 years of discoveries" — October 2026
• Cosmic Herald — "Five Years In, NASA's Lucy Is Under a Year From Its First Trojan Asteroid" — October 22, 2026
• Southwest Research Institute — Lucy mission five-year summary — October 19, 2026
• Discover Science — "NASA Lucy found asteroid Donaldjohanson turns end-over-end" — October 2026