ESA’s Mars Orbiter Crucially Refines Path of Interstellar Comet 3I/ATLAS

Since the discovery of interstellar comet 3I/ATLAS on July 1, 2025, astronomers around the globe have been diligently working to chart its path through the Solar System. The European Space Agency (ESA) has significantly enhanced the predicted trajectory of this celestial body, achieving a tenfold increase in accuracy by using data from the ExoMars Trace Gas Orbiter (TGO) currently in orbit around Mars.

This innovative approach demonstrated that Mars-based observations can play a critical role in understanding interstellar comets, even when they pose no threat to Earth. The TGO collected crucial data between October 1 and 7, 2025, as 3I/ATLAS made a relatively close pass to Mars, coming within approximately 29 million kilometers. This proximity allowed the orbiter to gather observations that were ten times closer than those obtained from Earth, providing a fresh perspective on the comet’s trajectory. The collaboration of data from the TGO and terrestrial telescopes allowed scientists to significantly refine the predicted path of 3I/ATLAS, enhancing the precision of their calculations.

The task of using the Mars orbiter’s data required overcoming unique challenges. The TGO’s CaSSIS instrument, originally designed to observe the Martian surface, had to be reoriented to capture images of 3I/ATLAS moving against the backdrop of stars. This adjustment required careful coordination among various ESA teams, including those specializing in flight dynamics and scientific instrumentation. The successfully submitted data on 3I/ATLAS marks a historical moment as it is the first time astrometric measurements from a spacecraft in orbit around another planet have been accepted into the Minor Planet Center’s database, which consolidates observations of comets and asteroids from multiple sources.

While 3I/ATLAS poses no danger to Earth, this endeavor serves as a vital test case for planetary defense strategies. ESA routinely monitors near-Earth objects to calculate their orbits and provide timely warnings if necessary. The exercise with 3I/ATLAS has highlighted the utility of triangulating measurements from both Earth and spacecraft located in space, enhancing readiness for possible future threats.

Currently, the comet is being observed by ESA’s Jupiter Icy Moons Explorer (Juice), though it is positioned farther away than the Mars orbiter. Juice is capturing data just after the comet’s closest approach to the Sun, when its activity is heightened. However, results from these observations are not expected until February 2026.

Looking ahead, ESA is also working on the Neomir mission, designed to fill the observational gap created by the Sun’s glare, which can obscure nearby asteroids and comets. This mission aims to detect near-Earth objects from a position between the Sun and Earth, potentially providing crucial early warnings of incoming threats.

Further, the agency is preparing the Comet Interceptor mission, which aims to gather insights from a comet, ideally targeting an interstellar one in the future. As comets like 3I/ATLAS provide unique links to our galaxy, missions like these deepen our understanding of the cosmos and solidify humanity’s connection to the greater universe.