NASA’s Hubble Space Telescope and ESA’s JUICE spacecraft have delivered a new wave of data on interstellar comet 3I/ATLAS, the third confirmed object ever detected traveling through our solar system from another star system. Observations spanning mid-2025 through early 2026 have pinned down the comet’s nucleus size, tracked its dust output, and captured jets and filaments in its coma, giving scientists the most detailed portrait yet of a body formed around a distant, unknown star.
From First Light to Nucleus Detection
The ATLAS survey telescope in Chile first spotted the object on July 1, 2025. Within weeks, Hubble turned its optics toward the comet and captured an image on July 21, when 3I/ATLAS was 277 million miles from Earth. That early image, reported in August 2025, showed a bright dust plume and a well-defined tail, clear signs that the comet was actively shedding material as solar heating intensified on approach to perihelion. Hubble’s data also provided a first constraint on the nucleus size, setting an upper limit while suggesting the solid body could be considerably smaller.
The comet was formally confirmed as a comet on September 8, 2025, settling early speculation about its nature. That confirmation rested on the detection of a gaseous coma, the fuzzy envelope of sublimated ices and dust that distinguishes a comet from an inert asteroid or an ambiguous object like the first interstellar visitor, 1I/’Oumuamua. Scientists emphasized that the clear presence of a coma and tail meant 3I/ATLAS was not an artificial object or inert shard, but an active icy body behaving in line with expectations for a true cometary visitor.
Hubble’s Post-Perihelion Follow-Up
Hubble did not stop at a single snapshot. The telescope reobserved 3I/ATLAS on November 30, 2025, using its Wide Field Camera 3 (WFC3) instrument. By that date the comet had passed its closest approach to the Sun and was moving outward, which made the observation a test of how its activity changed once peak heating had passed. Tracking that shift matters because the rate at which a comet’s dust and gas output rises and falls after perihelion reveals how deeply heat penetrates the surface and how volatile-rich the interior is.
A research team led by Hui, Jewitt, Mutchler, Agarwal, and Kim then analyzed Hubble data collected from December 2025 through January 2026. Their preprint reported a successful detection of the nucleus itself, separated from the surrounding coma glare. They quantified the nucleus size through an albedo-cross-section product, deriving an effective radius by assuming a comet-like albedo, and placed constraints on the body’s shape and rotation. Those shape constraints are significant: an elongated or irregular nucleus would sublimate unevenly, producing asymmetric jets, while a more spherical body would lose material more uniformly. The distinction feeds directly into models of how the comet was assembled in its home system and how it was later ejected into interstellar space.
Hubble’s time series also let the team estimate changes in dust production. By measuring the brightness profile of the coma at different distances from the nucleus, they inferred how much material was being lifted off the surface and how that rate evolved as the comet receded from the Sun. Such measurements, combined with dynamical models of the comet’s trajectory, help reconstruct how 3I/ATLAS responded to solar heating over its entire passage through the inner solar system.
JUICE Adds a Second Vantage Point
While Hubble watched from Earth orbit, ESA’s Jupiter Icy Moons Explorer (JUICE) seized a rare opportunity during its cruise phase. The spacecraft’s navigation camera captured 3I/ATLAS on November 2, 2025, using a partial-frame early download strategy to get data back to Earth quickly. Two days later, on November 4, JUICE made its closest approach to the comet at approximately 66 million km. Five onboard science instruments collected data during the campaign, turning what was originally a navigation exercise into a coordinated science effort.
The payoff from that campaign became clearer when ESA released imagery from JUICE’s dedicated science camera showing the comet’s coma, tail, jets, and filaments. Those fine structures are telling. Jets indicate localized active regions on the nucleus surface where volatile ices are exposed, while filaments in the tail suggest complex interactions between outflowing dust and the solar wind. Analysis of the JUICE data involves teams working with four instruments (MAJIS, UVS, SWI, and PEP), each probing different wavelengths and particle populations to build a multi-layered view of the environment around 3I/ATLAS.
Because JUICE viewed the comet from a very different angle than Hubble, its images trace how dust and gas flow away from the nucleus into space. Subtle bends or kinks in the tail can reveal changes in the solar wind or in the comet’s own activity. When combined with Hubble’s measurements of the nucleus brightness and coma structure closer in, JUICE’s wide-field view offers a way to connect small-scale processes at the surface with the large-scale architecture of the tail.
Why Two Missions See More Than One
Most coverage of 3I/ATLAS has treated the Hubble and JUICE observations as separate milestones. But their real value lies in the combination. Hubble excels at resolving the nucleus from the coma in visible light and measuring dust-loss rates over time. JUICE, observing from a different position in the inner solar system, captured structural detail in the coma and tail that complements Hubble’s nucleus-focused work. Together, the two datasets could test whether the post-perihelion jets Hubble tracked correspond to the localized active regions JUICE imaged, a link that would point to a heterogeneous nucleus with layers or patches of different volatile composition.
That kind of layered structure would carry information about how the comet originally formed. If the outer shell sublimates faster than the interior, for example, the surface may be dustier and less volatile-rich than deeper layers, implying a history of gradual erosion. Alternatively, patchy activity could signal that the nucleus is a rubble pile assembled from smaller icy fragments, each with its own composition. Comparing the timing of brightness changes seen by Hubble with the appearance and evolution of jets in JUICE imagery will be crucial for distinguishing between these scenarios.
NASA has emphasized that multi-mission campaigns like this one are becoming a hallmark of its planetary science strategy, using assets across the agency to study transient targets. A dedicated overview of 3I/ATLAS observations describes how Hubble, JUICE, and ground-based telescopes together provide multiple lenses on the interstellar visitor, turning a brief encounter into a richly sampled experiment in comparative planetology.
A Broader Interstellar Context
3I/ATLAS follows in the footsteps of 1I/’Oumuamua and 2I/Borisov, but it is the first interstellar object to be tracked with such a coordinated space-based campaign. Unlike ‘Oumuamua, whose lack of a clear coma and unusual acceleration left its composition ambiguous, 3I/ATLAS is unambiguously cometary. And unlike 2I/Borisov, which was studied largely from the ground, 3I/ATLAS benefits from sensitive space telescopes and a planetary mission passing nearby. This progression reflects a growing readiness to respond quickly when new interstellar objects are discovered.
Across NASA’s broader portfolio, planners are already considering how future missions might rendezvous with or even sample such objects. For now, however, the focus is on extracting every possible clue from remote sensing. Spectroscopic data, dust production curves, and tail morphology all feed into models of how small bodies form around other stars, how they are perturbed into unstable orbits, and how they are ultimately ejected into interstellar space. Each new object offers a point of comparison with comets native to our own solar system.
Public interest in 3I/ATLAS has been amplified by regular updates from mission teams and agency communications channels. Coverage in NASA news releases has highlighted the interplay between astronomy and planetary science, while technical updates have stressed the importance of rapid data analysis to capture a target that will never return. As with earlier interstellar visitors, the window for observation is measured in months, not years.
Scientific results from the Hubble and JUICE campaigns are expected to appear in peer-reviewed journals over the coming year. As new papers are accepted, they will be added to recently published listings that track the latest findings from NASA-supported research. Those studies will refine estimates of the nucleus size, density, and rotation state, and will likely offer competing interpretations of the internal structure. Some teams may argue for a relatively pristine, monolithic body, while others may favor a more processed, fragmentary object assembled from earlier collisions.
Whatever the final verdict, 3I/ATLAS underscores how quickly the study of interstellar small bodies is maturing. In less than a decade, the field has moved from the surprise of a first detection to the routine expectation that space telescopes and planetary missions can pivot to observe these fleeting visitors. With survey facilities improving and coordination across missions deepening, the next interstellar comet may arrive to find not just a welcoming array of instruments, but a scientific community ready to read its history in unprecedented detail.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
