Overview: A Rare Interstellar Visitor in Our Solar System
The interstellar comet 3I/ATLAS has captured the attention of space agencies around the world as it speeds through our solar system. First spotted in July 2025 by the ATLAS telescope in Chile, 3I/ATLAS is only the third known interstellar object to pass through our cosmic neighborhood. Its extrasolar origin is evident from its hyperbolic trajectory and an astonishing velocity of about 219,000 km/h (130,000 mph), which means it will not complete an orbit around the Sun the way planets and comets born in our system do. Ground-based observatories will have a visible window until September 2025, after which the object moves too close to the Sun to be easily tracked from Earth.
A Strategic Window for Real-Time Study
Even as 3I/ATLAS fades from Earth-based telescopes, a fleet of spacecraft already in the inner solar system will keep watching. ESA has coordinated observations using mission assets initially designed for Mars and Jupiter exploration to maximize our understanding of this alien visitor. From their vantage points near the Sun’s path, these spacecraft can continue collecting data long after 3I/ATLAS becomes difficult to observe from Earth-based facilities.
Targets and Timing: Mars, Sun, and Beyond
Between 1 and 7 October, Mars Express and the ExoMars Trace Gas Orbiter will observe the comet as it passes near Mars, with the closest approach between the probes and the comet at about 30 million kilometers on 3 October. In parallel, NASA’s Psyche mission—on its way to the main-belt asteroid 16 Psyche—will also capture data on 3I/ATLAS from a different vantage point, adding to the cross-check of measurements from multiple spacecraft.
Why Perihelion Matters: The Comet’s Brightest Phase
From late October into November, the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) will turn its instruments toward 3I/ATLAS. Observations are planned between 2 and 25 November, aligning with the comet’s perihelion—the point in its orbit closest to the Sun. This is when solar heating drives the strongest outgassing, vaporizing ices in the nucleus and creating a luminous coma and a long tail that trails behind the object. This active phase yields the best chance to determine the comet’s chemical makeup, surface ice composition, and dust content.
What Scientists Hope to Learn
3I/ATLAS presents a rare opportunity to compare an object formed around another star with comets native to our own solar system. If its chemical fingerprint resembles familiar materials—water ice, silicates, and organic compounds—it could imply universal building blocks for planetary systems. Conversely, striking differences might reveal exotic ingredients or processing histories from another star’s protoplanetary disk. Either outcome enriches our understanding of how common certain materials are across the galaxy and how planetary systems assemble their small bodies.
The Value of a Coordinated, Multi-Platform Approach
Observing 3I/ATLAS with Mars orbiters (Mars Express, ExoMars Trace Gas Orbiter), a NASA planetary mission (Psyche), and the JUICE spacecraft circling Jupiter’s moons exemplifies how international collaboration can maximize science. Each observer provides different angles, instruments, and sensitivities, enabling a richer, cross-validated picture of the comet’s nucleus, activity, and debris environment. ESA notes that such a multi-vantage approach will yield the most valuable data during the peak activity window around perihelion, when the comet is closest to the Sun and its signature gases and dust are most detectable.
Looking Ahead: What This Means for Astrophysics
As 3I/ATLAS completes its swing past the inner solar system, researchers anticipate a deeper understanding of interstellar material. The study will not only help characterize 3I/ATLAS itself but also inform models of how material is transported between stars and how planetary systems evolve. If more interstellar visitors are detected in the future, the baseline established by 3I/ATLAS and its Earth- and space-based observations will guide how we interpret subsequent encounters, potentially rewriting assumptions about the diversity of planetary building blocks across the Milky Way.
In Summary: A Mission-Supported Window into the Galaxy
From early October through November, the combined efforts of Mars orbiters, Psyche’s route, and JUICE will keep 3I/ATLAS in the scientific spotlight. This coordinated campaign, leveraging spacecraft designed for Mars and Jupiter exploration, aims to unlock the comet’s most intimate secrets during its highest-activity phase. The knowledge gained promises to illuminate the broader story of where our solar system’s materials come from and how common—and how surprising—the ingredients of planetary systems can be across the galaxy.
