At roughly 250,000 kilometers per hour, comet 3I/ATLAS did not merely enter the inner solar system; it tore through it at a speed that made every observation window brief and technically demanding. That urgency helps explain why NASA’s close-range images from Mars have drawn so much attention: they show a visitor from another star system passing within about 18.6 million miles away, a rare geometry for an interstellar object.
The comet was first reported on July 1, 2025 by the NASA-funded ATLAS survey in Chile, and it quickly became clear that its path was not the closed loop of an ordinary solar system comet. Its hyperbolic orbit identified it as only the third known interstellar object ever seen crossing the Sun’s neighborhood, following 1I/’Oumuamua and 2I/Borisov. Unlike those earlier discoveries, 3I/ATLAS was found early enough for observatories on Earth and in space to watch it before, during, and after its swing toward the Sun.
The closest images came from the HiRISE camera on the Mars Reconnaissance Orbiter. From Mars orbit, HiRISE recorded the comet as a compact, bright coma rather than a dramatic long-tailed object, but that modest-looking target carried scientific weight. The resolution, about 19 miles per pixel, gave researchers a way to tighten estimates of the nucleus size and the surrounding dust environment. NASA’s Perseverance rover also turned its Mastcam toward the sky, while MAVEN added ultraviolet observations that traced hydrogen around the comet, offering clues to how much water was breaking apart in the coma.
That chemical angle matters because interstellar comets are more than moving ice and dust. They are preserved fragments of planetary construction from somewhere else in the galaxy. NASA’s broader campaign expanded far beyond Mars, drawing on multiple NASA assets including Hubble, Webb, PUNCH, Parker Solar Probe, Lucy, Psyche, SPHEREx, TESS, and SOHO. This wide spread of vantage points allowed astronomers to keep tracking 3I/ATLAS even when the comet moved too near the Sun for easy ground-based viewing. Images from heliophysics missions captured changes in the tail and jets around perihelion, turning what could have been a short observational episode into a solar system-wide experiment in coordinated comet science.
The most revealing chemistry came from the James Webb Space Telescope. Its infrared spectrum showed the coma held nearly eight times as much carbon dioxide as water vapor, a ratio that stands apart from almost every well-studied comet native to the solar system. “I have never seen such a strong CO2 peak in a comet spectrum,” said Martin Cordiner of NASA Goddard. Because Earth’s atmosphere blocks those wavelengths, that result depended on Webb alone.
The comet’s speed and direction add another layer of intrigue. NASA notes that 3I/ATLAS arrived from the direction of Sagittarius, and follow-up orbital work has linked its motion to older stellar populations in the Milky Way. That fits with the view that 3I/ATLAS may be extremely ancient, possibly carrying ices that formed long before the Sun and planets existed.
Its flyby is over in practical terms, but the science is not. Newer observations from late 2025 and early 2026, including Hubble, SPHEREx, and TESS, are still extending the record of how the comet brightened, rotated, and shed material after perihelion. For planetary scientists, 3I/ATLAS has become less a fleeting spectacle than a benchmark object: a rare chance to compare the solar system’s comets with one that formed somewhere else entirely.
