Interstellar guest returns to the spotlight
The interstellar wanderer 3I/ATLAS has yielded the closest images yet from a Mars-orbiting spacecraft, offering a rare glimpse of a visitor that did not begin in our solar system. European Space Agency (ESA) officials confirmed that the ExoMars Trace Gas Orbiter (TGO), along with NASA’s Mars Express, captured a sequence of images during the comet’s flyby of Mars on October 3. While the encounter was brief, the data are helping scientists refine estimates of the comet’s size, motion, and activity as it barrels toward the Sun.
What the images show
From about 30 million kilometers away, the comet appeared as a fuzzy, bright dot in the frame. The nucleus—the solid core of ice and rock—and its surrounding coma, the glowing envelope of gas shed as the nucleus warms, were the primary features visible in the animation produced by ESA from TGO data. As 3I/ATLAS approaches the Sun, the coma is expected to swell and may eventually develop a tail under the influence of solar wind and radiation pressure.
ESA notes that the instruments on TGO are optimized for studying Mars from a relatively close vantage point, which limits their ability to capture dim, fast-moving targets at such distances. “The comet is around 10,000 to 100,000 times fainter than our usual target,” explained a principal investigator involved with ESA’s Colour and Stereo Surface Imaging System. Consequently, the latest imagery does not reveal a tail in visible light, though researchers caution that a tail could still emerge as the comet heats up near perihelion.
Why 3I/ATLAS matters
3I/ATLAS is only the third confirmed interstellar object passing through our solar system, following 1I/’Oumuamua and 2I/Borisov. Early estimates place its diameter between 5 and 11 kilometers (3–7 miles), making it potentially the largest known interstellar visitor to date. Its trajectory and speed suggest it has raced through the galaxy for billions of years, predating our sun by a significant margin. Unlike comets formed in the solar protoplanetary disk, 3I/ATLAS likely carries material from another star system, offering a rare sample of extrasolar chemistry and geology.
What’s next for the encounter
At present, the comet is on the far side of the Sun, outside Earth’s view. Ground-based telescopes will resume tracking 3I/ATLAS in December, with additional observations anticipated as it heads toward a close approach to Jupiter in March 2026. After that encounter, the object will continue its journey away from the inner solar system, leaving us with a fleeting local glimpse of a traveler from another stellar neighborhood.
Implications for future interstellar studies
Analysts will pore over Mars-based imagery alongside data from other missions to better constrain the comet’s size, albedo, and possible composition. If a more reflective surface or unusual outgassing signatures emerge, researchers hope to glean clues about the materials that formed planets around a different star. The event also underscores the value of coordinated observations: even when a target is faint and distant, multiple spacecraft can piece together a clearer picture of its behavior and evolution.
As teams continue to study 3I/ATLAS, the public can expect updates as new data become available, including possible refinements to the comet’sestimated trajectory and physical characteristics. The interstellar visitor remains a remarkable reminder of how much there is still to learn about our cosmic neighborhood—and the wonders that lie beyond it.
