European Mars Orbiter Captures 3I/ATLAS During Distant Flyby
In a rare encounter with a traveler from beyond the solar system, the interstellar comet 3I/ATLAS passed by Mars on October 3, skimming within 19 million miles (about 30 million kilometers) of the Red Planet. The European Space Agency (ESA) reported that its Trace Gas Orbiter (TGO) used the Colour and Stereo Surface Imaging System (CaSSIS) to photograph the fleeting visitor as it ventured through the inner solar system. The effort illustrates how modern planetary missions can pivot to study extraordinary objects when the opportunity presents itself.
The Challenge of Imaging a Faint Interstellar Visitor
CaSSIS principal investigator Nick Thomas described the observation as exceptionally challenging. The comet, which is detectable only at a fraction of the brightness of typical targets, demanded the instrument’s finest sensitivity. 3I/ATLAS was estimated to be 10,000 to 100,000 times fainter than the standard targets CaSSIS routinely tracks, highlighting the delicate balance between exposure time and data quality during close-approach observations.
What 3I/ATLAS Tells Us About Interstellar Space
Discovered this past July by the ATLAS survey in Chile, 3I/ATLAS is only the third confirmed interstellar object visiting our solar system, following 1I/’Oumuamua and 2I/Borisov. The “3I” designation marks it as the third confirmed interstellar visitor. By studying such bodies, astronomers aim to glean clues about the materials and processes that prevailed in far-flung star systems, potentially billions of years before our own sun formed.
ESA’s Coordinated Campaign: Multiple Orbiters, One Object
The observation of 3I/ATLAS was part of a coordinated ESA effort to characterize the comet as it cruises through the inner solar system. ESA’s Mars Express, which entered Mars’ orbit in 2003, also attempted to image the comet on October 3. However, Mars Express data did not yield a clear capture at the same exposure settings used by CaSSIS. ESA noted that Mars Express recorded shorter exposure times (0.5 seconds) due to instrument constraints, compared with 5 seconds for CaSSIS on the Trace Gas Orbiter. This difference in imaging parameters contributed to the variation in image clarity between the two missions.
What the Data Could Reveal
While the immediate images may be faint, they contribute to a broader dataset that helps scientists understand the composition and dynamics of interstellar objects. The study of 3I/ATLAS complements other measurements—such as the comet’s trajectory, speed, and spectral properties—which together build a more complete picture of this ancient traveler’s origins. ESA officials emphasized that interstellar comets carry information about planetary formation in distant star systems, offering a rare glimpse into environments far beyond our own solar neighborhood.
Broader Exploration: JUICE and the Search Continues
ESA’s ongoing exploration of the outer solar system continues to broaden with the Jupiter Icy Moons Explorer (JUICE) mission, which is heading toward Jupiter with plans to observe 3I/ATLAS as it proceeds through the solar system. JUICE will begin targeted observations around November 2, coordinating with the comet’s solar approach to maximize scientific return. The cross-mission collaboration underscores how multiple spacecraft can provide a richer, multi-angle view of a single interstellar visitor.
Looking Ahead
As 3I/ATLAS journeys toward its closest approach to the sun and onward into interstellar space, scientists are eager to assess any additional data that could emerge as the object continues to dim. The coming months may bring new detections from other orbiters, including ESA’s ongoing Mars missions and interplanetary probes en route to more distant destinations. Each data set helps the scientific community refine models of cometary behavior, materials, and the broader narrative of how our solar system interfaces with the wider galaxy.
In the end, the encounter serves as a reminder that even in well-mapped frontiers like Mars, the cosmos still offers unexpected guests—bringing opportunities to test instruments, challenge assumptions, and expand our understanding of the universe.
