NASA Spacecraft Capture Rare Views of Interstellar Comet

When comet 3I/ATLAS disappeared behind the Sun in October 2025, astronomers faced a critical challenge: how to continue studying this rare interstellar visitor during its closest approach to our star. The solution came from an unexpected source—NASA's fleet of solar-observing spacecraft, which turned their instruments toward the cosmic traveller and captured unprecedented images that are reshaping our understanding of objects from beyond our Solar System.

A Cosmic Visitor 7 Billion Years in the Making

Comet 3I/ATLAS didn't originate in our Solar System. This ancient wanderer formed approximately 7 billion years ago around a distant star elsewhere in the Galaxy, making it only the third known interstellar object to visit our cosmic neighbourhood. Its journey through our Solar System represents a fleeting opportunity for scientists—once it passes, 3I/ATLAS will disappear from view forever, taking its secrets with it unless we can learn everything possible during its brief visit.

The comet's passage behind the Sun from Earth's perspective in October created an observational problem but also an opportunity. While ground-based telescopes lost sight of the object, NASA's heliophysics missions stepped up to fill the gap. For the first time in history, these solar-observing spacecraft purposefully tracked an object from another star system, marking a significant milestone in interstellar astronomy.

Three Eyes on the Prize: NASA's Solar Fleet

The collaborative effort involved three major spacecraft, each bringing unique capabilities to bear on the faint, fast-moving comet.

STEREO-A: The Early Bird

NASA's Solar Terrestrial Relations Observatory spacecraft became the first to spot 3I/ATLAS, observing the comet from 11 September to 2 October 2025. STEREO's primary mission focuses on studying solar activity and its effects on the planets, but its Heliospheric Imager-1 instrument proved capable of capturing visible light images of the interstellar visitor.

The challenge? Scientists initially believed 3I/ATLAS would be too faint for detection. The solution came through an imaging technique familiar to astrophotographers: stacking. By overlaying multiple images, astronomers brought out minute details that would have remained invisible in single frames. The resulting composite revealed 3I/ATLAS as a hazy white blob against a background of pink and black streaks—proof that even faint interstellar objects can be captured with the right techniques.

PUNCH: Tracking Through the Corona

The Polarimeter to Unify the Corona and Heliosphere spacecraft normally tracks coronal mass ejections—powerful bursts of plasma erupting from the Sun's surface. Between 28 September and 10 October 2025, PUNCH redirected its gaze to follow 3I/ATLAS as it passed within 372 to 378 million kilometres of Earth.

PUNCH's observations revealed the comet's tail as a slight elongation extending toward the 4 o'clock position—a critical measurement for understanding how the interstellar object interacts with solar radiation and the solar wind. The spacecraft's frames captured not just the comet but also Mars streaking past, a reminder of the dynamic nature of our Solar System.

"We're really pushing the limits of the system," Kevin Walsh of the Southwest Research Institute in Boulder, Colorado, who led PUNCH's observations, told researchers. The team's success in detecting such a faint object against the Sun's glare demonstrates the versatility of NASA's solar observation network.

SOHO: The Veteran Observer

The Solar and Heliospheric Observatory, jointly operated by NASA and the European Space Agency, brought decades of comet-spotting experience to the effort. Since launching in 1995, SOHO has observed more comets than any other space mission. Through the NASA-funded Sungrazer Project, with assistance from citizen scientists, SOHO images have led to the discovery of more than half of all known comets.

Between 15 and 26 October 2025, SOHO's Large Angle and Spectrometric Coronagraph instrument suite tracked 3I/ATLAS from a distance of 358 million kilometres—more than twice the Earth-Sun distance. Once again, image stacking proved essential for bringing the comet clearly into view despite expectations that it would be too faint to detect.

A Global Effort: Mars Joins the Observation Campaign

While NASA's solar missions tracked 3I/ATLAS from their vantage points, spacecraft at Mars also contributed crucial data. The European Space Agency's ExoMars Trace Gas Orbiter captured images of the comet in the Martian sky on 3 October 2025. These observations from a different location in the Solar System enabled scientists to recalculate the comet's trajectory with unprecedented precision.

The Mars observations complemented earlier ground-based images from facilities like the Gemini South telescope at Cerro Pachón in Chile and the Hubble Space Telescope, creating a comprehensive dataset spanning multiple wavelengths and viewing angles.

Why These Observations Matter

The coordinated campaign to observe 3I/ATLAS as it passed behind the Sun wasn't just about capturing pretty pictures. Scientists used these observations to gather critical information about the comet's size, physical properties, and chemical makeup—data that will help us understand the conditions around other stars and the building blocks available for planet formation throughout the Galaxy.

Interstellar objects are rare visitors. Before 3I/ATLAS, only two other confirmed interstellar objects have passed through our Solar System. Each one represents a sample of material from a completely different stellar environment, offering insights impossible to obtain any other way. Once these objects leave our neighbourhood, they're gone forever, making every observation precious.

The successful detection of such a faint object by solar missions not designed for deep-space observation also demonstrates the adaptability of NASA's spacecraft fleet and the power of modern image processing techniques. The stacking methods used to bring 3I/ATLAS into view are the same ones amateur astrophotographers use, proving that professional and amateur astronomy share common technical foundations.

Looking Ahead: The Final Chapter

As of late November 2025, comet 3I/ATLAS has reemerged from behind the Sun and is once again visible from Earth—though it continues to fade as it speeds away from our Solar System. Astronomers are racing against time to extract every possible piece of information before the interstellar visitor disappears forever.

The observations from NASA's solar missions have already contributed to refining our understanding of 3I/ATLAS's orbit, composition, and behaviour. Combined with data from Mars orbiters and ground-based telescopes, these images form part of a comprehensive portrait of an object that formed when our Solar System was still in its infancy.

For those inspired to catch a glimpse of this cosmic wanderer before it departs, ground-based observation remains possible, though the comet continues to dim. The legacy of 3I/ATLAS, however, will endure in the scientific data collected during its brief passage—a testament to human ingenuity and our relentless curiosity about the universe beyond our own stellar neighbourhood.

As we bid farewell to this 7-billion-year-old traveller, one thing remains certain: the next interstellar visitor will find us better prepared, with techniques refined and missions ready to capture every moment of its journey through our cosmic backyard.