Mars Probes Capture Interstellar Comet's Closest View

Two spacecraft circling Mars have done something no telescope on Earth could: they photographed a visitor from another star system from closer than anyone has ever managed. Between October 1, 2026 and October 7, 2026, the European Space Agency's ExoMars Trace Gas Orbiter and Mars Express turned their cameras toward interstellar comet 3I/ATLAS as it swept past the Red Planet. At its closest, on October 3, 2026, the comet came within about 30 million kilometers of the two orbiters — roughly 18.6 million miles away — nearer to Mars than Earth will ever get to this icy traveler. In the released images, the comet is just a small, fuzzy white dot drifting across the frame. But that humble dot is the glowing heart of only the third confirmed interstellar object ever found.

The pictures came from the Colour and Stereo Surface Imaging System (CaSSIS) aboard the ExoMars orbiter — a camera built to photograph the bright surface of Mars from a few hundred kilometers away, not a dim speck of ice tens of millions of kilometers out in the dark. To catch the interstellar comet at all, the science team stacked multiple five-second exposures into a single sequence. In the resulting animation, 3I/ATLAS appears as a slightly fuzzy dot moving downward through a field of streaked stars, as reported by Live Science. That fuzziness is the comet's coma: a halo of gas and dust a few thousand kilometers wide, boiling off the nucleus as sunlight warms it. Resolving the solid nucleus itself was never on the table — imaging it would have been like spotting a mobile phone sitting on the Moon from Earth.

“This was a very challenging observation for the instrument,” said Nick Thomas, the principal investigator for the CaSSIS camera, according to Earth.com. The interstellar comet glowed an estimated 10,000 to 100,000 times fainter than Mars, the camera's usual subject — a staggeringly dim target for optics designed for a bright, nearby world. The mission teams were genuinely unsure what to expect before they tried. The sibling spacecraft Mars Express fared worse: its cameras simply were not sensitive enough to pick the visitor out of the black.

Why this interstellar comet was almost impossible to photograph

Both spacecraft normally point their cameras at one of the brightest objects in the sky: Mars itself, sitting just hundreds to a few thousand kilometers below them. Pointing those same cameras at a far dimmer object tens of millions of kilometers away was an experiment in pushing hardware far beyond its design brief. The scientists stacked exposure after exposure to coax the faint signal out of the noise, and the result was a clear detection of the coma — proof the interstellar comet is active and shedding material. The full extent of that gas-and-dust halo could not be measured, because its brightness drops off so quickly with distance from the nucleus that it fades into background noise. The distant interstellar comet never resolved into more than a point of light, but that point of light told the whole story.

A sharper path from an unlikely observatory

The real payoff was not the picture but the precision. Because the ExoMars orbiter sat roughly ten times closer to the comet than any telescope on Earth, its data supplied a second viewpoint — a completely different viewing angle across the Solar System. According to Phys.org, triangulating the Mars-based measurements with Earth-based telescope data sharpened the predicted trajectory of the interstellar comet 3I/ATLAS by a factor of ten, far beyond the modest improvement scientists had expected. The uncertainty in the comet's future location shrank dramatically, and the measurements became the first astrometric data ever taken from a spacecraft orbiting another planet to be accepted into the Minor Planet Center's official database.

That matters beyond curiosity. ESA's planetary-defense teams practice exactly this kind of work: pinning down where a fast-moving object is heading so they can warn in time if one ever threatens Earth. This icy wanderer poses no danger — it is racing outward and will never return — but it made a perfect rehearsal. As the agency's own analysis noted, a second location in space turns a fuzzy guess into a firm fix, and borrowing instruments never built for asteroid detection proved surprisingly powerful.

How the third interstellar comet made its way to Mars

The story began on July 1, 2025, when the ATLAS survey telescope in Chile flagged a fast-moving object entering the Solar System. It was soon confirmed as only the third interstellar object ever detected, following 1I/’Oumuamua in 2017 and 2I/Borisov in 2019. Unlike the strange, rocky ’Oumuamua, this visitor behaves like a proper comet, growing a glowing coma as it nears the Sun. Some estimates suggest its material could be around 3 billion years older than the entire Solar System — a genuine fossil from another star's nursery, according to Earth.com. It is tearing through our neighborhood at speeds reaching 250,000 kilometers per hour, and once it passes, it will vanish into interstellar space forever.

Naturally, the internet had its moment of speculation about whether a visitor from another star could be something artificial. But the observations point the other way: the growing, sunlight-driven halo of gas and dust is the classic signature of a natural comet, exactly what mission scientists described seeing as the object warmed on its approach to the Sun. Inert rocks do not puff out comas. The fuzziness that made the images so hard to take is precisely the evidence that 3I/ATLAS is what astronomers said it was.

What happens to the visitor next

With the trajectory now pinned down with far greater precision, ground-based observatories can aim their instruments at the interstellar comet with real confidence, squeezing out detailed science before it is gone for good. ESA's Jupiter-bound Juice probe also watched the object later in 2026 as it neared the Sun, seeing it in a far more active state — wrapped in a bright halo with a long tail streaming behind it, according to the agency's follow-up reporting. The agency is already building on the lesson: its planned Comet Interceptor mission stands ready to visit a pristine comet one day, and it might just get an interstellar target.

For skywatchers, the lesson is simple. One interstellar comet, two aging cameras at Mars, and a sharper map of its path than anyone thought possible — achieved with hardware that was never meant for the job. When the next such traveler arrives, humanity will be better at tracking it than it was before October 2026. Find more astronomy coverage on our science topic page, including the recent sighting of a neutron-star merger glowing for nine minutes.