NASA Lucy Locks In Camera Settings for Trojan Flybys No Telescope Can Preview

NASA's Lucy spacecraft has spent this spring imaging four of its primary Trojan asteroid targets using its high-resolution L'LORRI camera - not to gather science yet, but to solve a specific engineering problem that no Earth-based observatory has ever been able to address: what these ancient space rocks actually look like when you're not staring at them straight into the sun. Mission scientists have published the update today. The mission team completed downloading and processing those calibration images in July 2026, and the resulting camera settings will shape what Lucy can deliver when it reaches its first Trojan target, Eurybates, in August 2027.Every time astronomers on Earth have photographed Jupiter's Trojan asteroids - the two swarms of ancient rocky bodies that orbit the Sun at the same distance as Jupiter - they have seen them from roughly the same direction as the Sun itself. The result looks like a full Moon: fully illuminated, with shadows tucked out of sight on the far side. Lucy's flyby geometry is fundamentally different. As the spacecraft swoops past each Trojan at between 12,750 and 19,680 mph (roughly 5.7 to 8.8 km/s), it will approach from the side - with solar phase angles ranging from 54 degrees to 82 degrees depending on the target. That means surfaces will be partly in shadow. Camera settings calibrated for full illumination will produce images that are either too dark or washed out.Why Trojan Asteroids Appear Darker From Lucy's Perspective Than From EarthThe physics here is straightforward but easy to miss. Phase angle is the angle formed between the Sun, the asteroid, and the observing spacecraft. From Earth, Trojans have a phase angle near zero - sunlight coming almost directly from behind the observer, flooding the surface evenly. Lucy's flybys involve phase angles of 54 to 82 degrees - approaching from the side, with the Sun casting shadows across craters, ridges, and slopes. This is actually scientifically valuable: shadows are what reveal topography. But it requires knowing in advance how much light the camera will receive, or the exposure will be wrong.The solution is to image the targets ahead of time, from the approaching spacecraft's vantage point, to measure how bright each asteroid appears at the specific angles Lucy will encounter. This spring - late March through early April 2026 - Lucy turned its L'LORRI camera toward Eurybates, Polymele, Leucus, and Orus as they appeared as faint, moving specks against the star field. The images arrived at mission control and were fully processed by July 2026. What the team got from each observation was not a surface map but a brightness measurement - the raw data needed to select optimal exposure times for each flyby.A Four-Instrument Arsenal Built for One-Time EncountersLucy carries four visible-light cameras, each with a distinct role in the encounter sequence. Understanding why calibration matters requires understanding how each instrument contributes.L'LORRI - the Lucy Long Range Reconnaissance Imager - is the mission's workhorse science camera. Built by the Johns Hopkins Applied Physics Laboratory, it is a Ritchey-Chr tien telescope, the same optical design used in the Hubble Space Telescope. Light enters the tube, reflects off a hyperbolic primary mirror, bounces back off a smaller hyperbolic secondary mirror, and focuses through an opening in the primary onto a lens assembly and a charge-coupled device (CCD) detector. The field of view is just 0.29 degrees - a narrow, pencil-thin window - and each pixel covers 1.0 arcsecond of sky. From 621 miles (1,000 km) away, that resolution translates to craters 229 feet (70 m) across being clearly distinguishable - the width of roughly two-thirds of a city block. After image deconvolution, surface features as small as about 33 feet (10 m) may become resolvable.The twin Terminal Tracking Cameras - T2CAM - play a different role. Their job is navigation: autonomously identifying the asteroid's position against the star field in the final hours of approach and keeping all of Lucy's instruments pointed at the target as the spacecraft shoots past. For that task, they need a wide field of view to accommodate the uncertainty in where exactly the asteroid will appear. The T2CAM's field of view is 11.0 degrees by 8.2 degrees (compared to L'LORRI's 0.29 degrees) - a large enough window to catch the asteroid even if its predicted position is slightly off. Once tracking locks on, the system can redirect the entire instrument platform to keep the target centered.The MVIC - Multicolor Visible Imaging Camera, part of the L'Ralph instrument suite - fills in the color picture. Where L'LORRI sees in black and white, MVIC captures images in five spectral bands spanning visible to near-infrared wavelengths. Those bands are specifically chosen to detect phyllosilicates (hydrated minerals), water-ice signatures, and other compositional markers. MVIC sweeps a wide swath of the asteroid surface in panoramic fashion, complementing L'LORRI's close-up shots.What Donaldjohanson Revealed: A Dress Rehearsal That Produced Real ScienceLucy arrived at this calibration campaign with more preparation than a typical interplanetary probe would have. Its April 20, 2025 flyby of the main-belt asteroid Donaldjohanson served as a full dress rehearsal for the Trojan encounters - and produced its own scientific results in the process.The spacecraft flew within 650 miles (1,050 km) of Donaldjohanson at 1:51 p.m. ET on April 20, 2025, collecting the first close-up data ever obtained of that object. The results, published June 18, 2026, in the journal Science, revealed three unexpected findings.First, Donaldjohanson turns out to wobble. Earth-based observers had measured it rotating end-over-end once every 10.5 days - but Lucy's data showed a second motion: the asteroid also wobbles around its long axis once every 26.5 days, like a spinning top losing its balance.Second, the asteroid's shape is bilobate - two connected lobes forming a peanut or dumbbell silhouette, most likely two fragments from a collision that drifted back together under mutual gravity 155 million years ago. Its rotation has been slowing ever since, driven by the YORP effect: the uneven way solar radiation heats and re-radiates from an irregularly shaped object, producing a tiny but persistent torque.Third, and most relevant to the Trojan mission: Lucy's infrared spectrometer detected iron-rich clay minerals on the asteroid's surface - phyllosilicates that can only form in the presence of liquid water. Donaldjohanson's iron-rich clays point to a brief episode of water presence, as opposed to the magnesium-rich clays found on carbon-rich asteroids Bennu and Ryugu that indicate prolonged water exposure lasting millions of years. "It's helpful for scientists to compare Donaldjohanson with asteroids like Bennu and Ryugu, which are seemingly similar asteroids, because every subtle difference is another clue to our origin story," said Simone Marchi, Lucy's deputy principal investigator at the Southwest Research Institute.The successful flyby demonstrated that the spacecraft's instruments work as designed and that the mission team is capable of executing the dense, precisely timed observation sequences the Trojan encounters will demand.What Does Lucy Aim to Learn From the Trojans?The Jupiter Trojan asteroids are often described as "fossils" of the early solar system - a metaphor that captures their significance more precisely than it might initially seem. Jupiter's Lagrange points, the gravitationally stable positions 60 degrees ahead (L4) and 60 degrees behind (L5) the planet in its orbit, act as natural reservoirs for material captured during the solar system's earliest, most chaotic phase. More than 13,000 Trojans have been discovered, with their numbers roughly comparable to the entire main asteroid belt.The leading theories of how the solar system settled into its current arrangement - particularly the Nice Model, which posits that Jupiter and Saturn migrated significantly inward after they formed - predict that the Trojans were not native to their current location. Instead, they are thought to have been scattered in from the outer solar system, possibly from the same primordial population that later became the Kuiper Belt. If true, the Trojans should carry compositional signatures of the cold outer solar system: volatile-rich, primitive materials unlike the drier, more processed asteroids of the main belt. Lucy's close-up spectral and compositional data from five or more distinct Trojan targets will be the first direct empirical test of this prediction."Once we start learning more about the Trojans, a completely different population of space rocks with very different histories, our understanding of solar system formation is destined to be challenged," Marchi said.Lucy will visit Trojans spanning every recognized taxonomic spectral class - C-type (carbon-rich), D-type, and P-type - and will observe both a collisional family member (Eurybates) and a near-equal-mass binary (Patroclus-Menoetius). That diversity was intentional: the mission was designed to survey the breadth of Trojan types, not merely pick the most accessible target.How Fast the Encounters Happen - and Why There Are No Second ChancesEach Trojan flyby is a single, high-speed pass. There is no orbiting, no slowing down, no second look. Lucy's instrument platform will lock onto the target, collect data for a window of hours around closest approach, and then the spacecraft will continue on its arc to the next target. The flyby distances range from roughly 270 to 774 miles (434 to 1,245 km) from each asteroid's center.The irreversibility of each encounter is why the spring 2026 calibration campaign matters. If engineers discover after arriving at Eurybates that the camera exposure settings are wrong, there is no recovery: the flyby will be over. The brightness measurements obtained from spring observations allow the team to lock in the best available settings before the encounter, reducing the risk of systematically under- or over-exposed imagery.Lucy's trajectory includes one more element worth noting: after its December 25, 2030 Earth gravity assist - which NASA describes as the first time a spacecraft will return to Earth's orbital vicinity from Jupiter's distance - it will use that gravitational boost to visit the L5 Trojan cluster. There, in March 2033, it will encounter Patroclus and Menoetius, a rare near-equal-mass binary pair in the trailing Trojan swarm.Is Eurybates' Lone Collisional Family a Relic of Ancient Trojan History?Eurybates holds a distinction no other Trojan target matches: it is the only known member of a confirmed collisional family within the L4 swarm. Collisional families form when a larger parent body breaks apart in a high-speed impact, scattering fragments that share similar orbital parameters and spectral properties. The fact that Eurybates represents the only such family in the leading Trojan swarm - while the main asteroid belt contains hundreds of families - raises a question the flyby may help answer: did the Trojans experience far fewer collisions than main-belt asteroids, or have family members simply drifted apart over billions of years?Eurybates also brings a bonus: it has a satellite. The Lucy team discovered Queta - estimated at roughly 1 km (0.6 miles) in diameter - from Hubble Space Telescope observations. On August 12, 2027, Lucy's flyby will resolve the shapes, surfaces, and orbital configuration of both bodies.How Does Lucy Actually Track an Asteroid During a High-Speed Flyby?Arriving at a small, dark asteroid at up to 19,680 mph (8.8 km/s) and keeping instruments trained on it for hours requires autonomous onboard navigation. Lucy cannot wait for commands from Earth - at its current distance, the round-trip communication delay can run to many minutes, far too long to correct a pointing error in real time.The T2CAM system handles this. In the hours leading up to closest approach, T2CAM continuously images the asteroid against the star background and calculates where the asteroid actually is relative to where trajectory models predicted it would be. That real-time position update is fed into the spacecraft's navigation system, which adjusts the Instrument Pointing Platform to track the target throughout the encounter. The T2CAM's wide field of view is large enough to accommodate the uncertainty in the asteroid's predicted position - an engineering choice that makes the autonomous tracking robust even when pre-encounter knowledge of the asteroid's orbit is imprecise.The calibration images from spring 2026 serve the navigation system too: knowing how bright each Trojan appears at varying distances and phase angles lets the T2CAM lock on to the target more reliably and earlier in the approach sequence.Frequently Asked QuestionsWhen will NASA's Lucy spacecraft reach the Trojan asteroids?Lucy's first Trojan encounter will be with Eurybates and its small satellite Queta on August 12, 2027. That will be followed by Polymele on September 15, 2027, Leucus on April 18, 2028, and Orus on November 11, 2028. After a third Earth gravity assist on December 25, 2030, Lucy will encounter the binary Trojan pair Patroclus and Menoetius in March 2033.Why does Lucy need to calibrate its cameras now, more than a year before the first flyby?The challenge is specific to flyby geometry. From Earth, Trojan asteroids appear almost fully lit - sunlight arriving from nearly the same direction as the observer. Lucy will approach each Trojan from the side, with phase angles of 54 to 82 degrees, meaning roughly half of each surface will be shadowed. Camera settings optimized for full illumination would produce images that are too dark or saturated. The spring 2026 observations allowed the team to measure how bright each target actually appears at those oblique angles and select exposure parameters accordingly. There is no opportunity to adjust settings once the flyby begins.What did Lucy learn from asteroid Donaldjohanson that matters for the Trojan mission?The April 2025 Donaldjohanson flyby was a dress rehearsal for the Trojan encounters, and it produced real science: iron-rich clay minerals on the asteroid's surface (indicating a brief episode of liquid water presence early in the asteroid's history), a wobbling two-axis rotation, and a bilobate peanut shape from two fragments slowly merging under gravity. All of Lucy's instruments performed as designed. The results were published in the journal Science in June 2026.How will the Trojan data test theories about how the solar system formed?The leading theory - the Nice Model - proposes that Jupiter migrated inward from farther out in the solar system, scattering material from the outer solar nebula into the L4 and L5 Lagrange points. If this is correct, the Trojans should carry compositional signatures of the cold outer solar system: volatile-rich, carbon-rich, water-ice-bearing materials unlike the drier asteroids of the main belt. Lucy's spectral instruments will map the surfaces of eight Trojans representing every known spectral class - a compositional survey that will either confirm or challenge those migration models directly.