Overview: A Rare Interstellar Visitor Near Mars
In a remarkable observational feat, a European Mars orbiter recorded imagery of the interstellar comet 3I/ATLAS as it whizzed past Mars on October 3. The flyby brought the comet to within about 19 million miles (30 million kilometers) of the Red Planet, providing scientists with a rare chance to study a visitor from beyond our solar system. The European Space Agency’s (ESA) ExoMars Trace Gas Orbiter (TGO) photographed the object using its Colour and Stereo Surface Imaging System (CaSSIS).
How TGO Captured the Encounter
The CaSSIS instrument is designed to map and analyze the Martian surface, but the interstellar nature and faintness of 3I/ATLAS presented a significant challenge. CaSSIS Principal Investigator Nick Thomas described the sighting as “a very challenging observation,” noting that the comet is roughly 10,000 to 100,000 times fainter than the orbiter’s usual targets. Despite the difficulty, ESA’s data show the instrument successfully acquired images as 3I/ATLAS moved through the Martian neighborhood.
The Interstellar Visitor: 3I/ATLAS
3I/ATLAS was discovered in July by the ATLAS survey telescope in Río Hurtado, Chile. The “3I” designation marks it as the third confirmed interstellar object observed in our solar system, following 1I/’Oumuamua (2017) and 2I/Borisov (2019). Interstellar comets like 3I/ATLAS carry material from other stellar systems and potentially offer unprecedented insight into the chemistry and formation of distant planetary systems.
What the Data Tell Us About the Comet
ESA officials emphasize that interstellar visitors hold clues about worlds far beyond our own. For 3I/ATLAS, researchers suspect an origin that predates the formation of our solar system by billions of years, making it one of the oldest comets ever observed. The current observation campaign, part of a broader ESA effort, aims to glean details about the comet’s composition, structure, and trajectory, enriching our understanding of how such objects travel through the galaxy.
Mars Observatories: A Concerted Effort
While CaSSIS on TGO captured the closest views, other Mars missions joined the effort. ESA’s Mars Express also attempted imaging during the October 3 pass, but the short exposure window posed limits. Mars Express operations cited exposure time constraints—0.5 seconds maximum—compared with ExoMars TGO’s longer exposures, which aided in producing more detectable signals from the faint interstellar target.
Looking Ahead: More Observations to Come
ESA officials highlighted that Mars orbiters persistently contribute to Mars science while adapting to unexpected events like the 3I/ATLAS flyby. Colin Wilson, ESA’s Mars Express and ExoMars project scientist, noted the excitement and the value of the data that will emerge after further analysis. The interest is not limited to European missions; NASA and other partners remain attentive as the comet continues its journey through the solar system.
A Glimpse Toward Jupiter: JUICE and Beyond
ESA’s JUICE (Jupiter Icy Moons Explorer) mission will also turn its gaze toward 3I/ATLAS in the coming months. With the comet’s solar approach peaking around late October to early November, JUICE is scheduled to begin targeted observations on November 2, three days after the comet’s perihelion close to the Sun. This multi-spacecraft, cross-mission interest underscores a growing global effort to study interstellar travelers as they traverse our cosmic neighborhood.
Why This Matters for Astronomy
Interstellar objects like 3I/ATLAS offer a unique window into the materials and environments of distant star systems. Each observation provides data about the composition of comets formed in other regions of the galaxy, potentially revealing differences and commonalities with our own solar system’s building blocks. As measurement techniques improve and more instruments join the effort, we may unlock deeper insights into the origins of planetary systems and the processes that shape them.
