Interstellar visitor 3I/ATLAS sparks a coordinated, multi-mission observing campaign
The skies over our solar system are briefly hosting a visitor from beyond. Interstellar comet 3I/ATLAS was first spotted in July 2025 by the ATLAS telescope network in Chile, marking it as the third known object from outside our solar neighborhood to sail through the inner solar system. Its extrasolar origin is evident from its hyperbolic trajectory and a velocity of about 219,000 km/h (roughly 130,000 mph), which means it will not complete a return voyage. While ground-based observers can still glimpse 3I/ATLAS through September 2025, astronomers project that the comet’s path will soon pull it behind the Sun from Earth’s perspective, ending most Earthbound chances to study it directly.
A strategic, multi-mission approach to studying a fleeting visitor
Rather than relying solely on telescopes on Earth, space agencies have mobilized a fleet of probes already in orbit around Mars and the outer planets. From the sun-facing side of 3I/ATLAS’s trajectory, these spacecraft can keep it in view even as it slips out of reach of terrestrial observers.
Between 1 and 7 October, ESA’s Mars Express and the ExoMars Trace Gas Orbiter (TGO) will observe the comet as it passes near Mars, with a closest approach of about 30 million kilometers anticipated on 3 October. NASA’s Psyche mission, en route to the large asteroid 16 Psyche in the main belt between Mars and Jupiter, will also track the interstellar visitor. Then, from 2 to 25 November, ESA’s Jupiter Icy Moons Explorer (JUICE) will turn its instruments toward 3I/ATLAS. JUICE’s observations are timed to coincide with perihelion—the moment the Sun’s heat drives the comet into its most active phase.
Experts note that the Mars- and Earth-based vantage points, along with the instruments on these spacecraft, provide a layered view of the comet’s behavior as it enters and exits the inner solar system. “JUICE near perihelion could provide the most crucial data,” says researchers familiar with mission planning, highlighting how the solar heating of ices at the nucleus creates a luminous coma and a long tail that reveal the comet’s chemistry in vivid detail.
Why perihelion is the window of opportunity
As 3I/ATLAS approaches its closest solar approach, solar radiation warms its core and triggers outgassing. The resulting plume of gas and dust offers scientists a chemical fingerprint—key information for comparing distant, interstellar building blocks with those forged in our own solar system. ESA emphasizes that observations during this peak activity will help determine the comet’s size, composition, and surface processes, turning a brief encounter into a rich data set.
What scientists hope to learn: clues about planetary systems beyond our own
3I/ATLAS presents a rare opportunity to probe whether comets born around other stars share familiar ingredients with locally formed bodies. If the chemistry aligns with that of solar system comets, it could imply universal building blocks pervade many planetary systems. If it diverges, researchers may uncover exotic materials that reveal different formation environments or evolutionary histories. In either case, the data will feed models of how planetary systems assemble and exchange material across the galaxy, offering a tangible glimpse into processes that sculpt worlds far beyond our own.
<h2 Looking ahead: what this means for our understanding of interstellar visitors
By coordinating observations across Mars orbiters, space telescopes, and the JUICE mission, scientists aim to stitch together a comprehensive portrait of 3I/ATLAS during its most active phase. The event underscores the value of cross-mission collaboration when chasing a transient, high-priority target from a distant star. As the data stream in, researchers will compare the interstellar visitor’s composition to known comets, refining theories about how planetary systems spread material through their galactic neighborhoods and potentially sharing common recipes for planetary systems across the Milky Way.
