ESA repurposes Mars and Jupiter missions to study interstellar comet 3I/ATLAS
The European Space Agency (ESA) is expanding the utility of its planetary missions by repurposing assets from Mars and Jupiter programs to monitor the interstellar visitor 3I/ATLAS as it hurtles through the inner solar system. Discovered in July 2025 by Chile’s ATLAS survey, 3I/ATLAS is only the third object confirmed to originate outside our solar system. Its hyperbolic trajectory and an astonishing speed of about 130,000 mph (219,000 km/h) mark it as a rare messenger from another star system.
Ground-based telescopes have a limited window to observe the comet, with visibility expected to wane by September 2025 as the object’s path takes it closer to the Sun. To fill this observational gap, ESA is coordinating an unprecedented collaboration that leverages existing spacecraft hardware that was not originally designed for interstellar studies.
Strategic use of Mars Express and ExoMars Trace Gas Orbiter
ESA’s Mars Express and the ExoMars Trace Gas Orbiter (TGO) will play a crucial role in near-term observations, focusing on 3I/ATLAS as it passes near Mars in early October. The closest approach is anticipated around October 3, when the comet will be roughly 30 million kilometers from Mars. In that window, the two Mars-focused orbiters will gather data on the comet’s activity, including its coma and dust environment, which are shaped by solar heating as the object travels through the inner solar system.
These observations aim to capture the early release of gases as 3I/ATLAS responds to solar radiation. By comparing these measurements with those from Earth-based telescopes earlier in the mission, scientists hope to map the composition of 3I/ATLAS and look for signatures that hint at the chemical processing that occurs in other star systems.
Broader multi-mission support: NASA and other orbiters
The effort is supported by a broader network of space assets, including NASA’s Psyche mission and other orbiters such as China’s Tianwen-1. The collaboration underscores a growing trend to repurpose and repurpose space assets beyond their original missions when a rare scientific opportunity arises. The mixed fleet will provide complementary viewpoints: some instruments will track dust and gas from the comet, while others monitor its trajectory and interaction with the solar wind.
JUICE’s critical post-perihelion observations
A centerpiece of ESA’s plan is the JUICE (Jupiter Icy Moons Explorer) probe, which is on a trajectory toward Jupiter. Although JUICE’s primary mission is not comet hunting, its position after 3I/ATLAS’ perihelion offers a unique vantage point when Earth-based observations become difficult due to solar glare. From late October through late November (November 2–25), JUICE will focus on 3I/ATLAS after its closest Sun approach. This period is when solar heating intensifies the comet’s activity, vaporizing ices in the nucleus and expanding the gas/dust coma and tail.
What scientists hope to learn
According to ESA and leading researchers, JUICE’s measurements, combined with data from Mars Express and TGO, will help reveal the chemical fingerprint of 3I/ATLAS. By analyzing the emitted gases and dust, scientists can compare the composition of this interstellar object with comets formed in our own solar system. Such comparisons may answer key questions about whether interstellar material carries different molecular inventories, and how common complex organic compounds might be across the galaxy.
“JUICE is best positioned for perihelion, when Earth observations are hardest,” noted scientist T. Marshall Eubanks, highlighting how this dedicated arrangement could fill observational gaps and deliver a holistic view of 3I/ATLAS’ behavior as it experiences peak activity. The aggregated data have the potential to refine models of interstellar delivery of materials and shed light on the broader dynamics of how matter travels between star systems.
Implications for our understanding of interstellar visitors
As interstellar comets like 3I/ATLAS enter and traverse the solar environment, they offer a rare, real-world test of theories about the materials that move between stars. ESA emphasizes that the mission data will reshape our understanding of how material migrates through the galaxy and possibly illuminate the pathways by which prebiotic compounds could be exchanged across planetary systems.
In sum, repurposing Mars and Jupiter mission assets to study 3I/ATLAS exemplifies how space agencies can pivot on opportunities to expand scientific horizons. The coming weeks and months are expected to yield a wealth of information about this extraordinary interstellar traveler and the broader processes that govern the exchange of matter in our cosmic neighborhood.
