In a remarkable feat of space observation, the European Space Agency’s (ESA) ExoMars Trace Gas Orbiter successfully captured the most detailed images to date of the enigmatic interstellar comet 3I/ATLAS as it made a swift passage by Mars in early October 2025. The photographs reveal distinct, fuzzy bright halos of gas, known as comas, enveloping the comet’s icy core. Interestingly, despite its interstellar journey, no tail was visible in these initial observations.
During its close encounter on October 3, the comet zipped past Mars at an astonishing speed of approximately 130,000 mph, maintaining a distance of about 30 million kilometers (18.6 million miles).
Mars Orbiters Race to Image the Elusive Comet
The ESA confirmed that several Mars orbiters, including the ExoMars Trace Gas Orbiter (TGO), focused their instruments on 3I/ATLAS on October 3. The TGO’s Colour and Stereo Surface Imaging System (CaSSIS) camera played a crucial role, recording multiple 5-second exposures. These images were then meticulously combined to create an animation, showcasing the comet as a faint, fuzzy white spot—its icy nucleus shrouded in a glowing cloud of gas, or coma.
Nick Thomas, the lead investigator for 3I/ATLAS, explained the challenge: the comet’s brightness is significantly lower, estimated to be between 10,000 and 100,000 times fainter than typical targets. This extreme faintness is why a conventional tail, often associated with comets, did not materialize in the captured images. Even the older Mars Express satellite attempted to photograph the comet, but its shorter 0.5-second exposures proved insufficient to properly resolve the distant object.
A Mysterious Visitor from Beyond Our Solar System
Comet 3I/ATLAS stands out as the third definitively identified interstellar object within our solar system, and potentially the largest one yet, boasting an estimated diameter of 511 kilometers. This ancient celestial wanderer has journeyed across the galaxy for billions of years, making it quite possibly the oldest comet ever observed—predating our own Solar System by several billion years.
After reaching its closest point to the Sun on October 30, 3I/ATLAS is expected to pass near Jupiter in early 2026 before eventually departing our solar system entirely, continuing its solitary voyage through the vast expanse of interstellar space.