The European Space Agency (ESA) is preparing for a unique celestial event: the observation of interstellar comet 3I/ATLAS as it journeys through our solar system. This rare visitor, identified as the third object known to originate from beyond our solar system, will be a significant target for multiple ESA spacecraft, offering an unparalleled chance to study its characteristics.
ESA's Mars orbiters, Mars Express and the ExoMars Trace Gas Orbiter, are scheduled to capture observations of 3I/ATLAS during its close approach to Mars on October 3, 2025. The comet is expected to pass within approximately 30 million kilometers (about 18.6 million miles) of the Red Planet. Instruments typically used for imaging Mars, such as Mars Express's High Resolution Stereo Camera (HRSC) and ExoMars TGO's Colour and Stereo Surface Imaging System (CaSSIS), will be repurposed to gather data on the comet's coma and tail.
Following its encounter with Mars, the ESA's Jupiter Icy Moons Explorer (JUICE) spacecraft, en route to Jupiter, will also turn its instruments toward 3I/ATLAS. These observations are planned between November 2 and November 25, 2025, shortly after the comet's closest approach to the Sun on October 30, 2025, at a distance of about 1.4 astronomical units (AU). This timing is crucial, as the comet is anticipated to be at its most active, displaying a prominent tail and a bright halo.
Comet 3I/ATLAS, discovered on July 1, 2025, by the ATLAS survey telescope in Chile, is distinct from its interstellar predecessors, 1I/'Oumuamua and 2I/Borisov. Unlike them, 3I/ATLAS is a true comet, featuring an icy nucleus surrounded by a gas and dust cloud. NASA's Hubble Space Telescope captured an image on July 21, 2025, revealing a teardrop-shaped dust cocoon around its nucleus and providing estimates for the nucleus's diameter between 440 meters and 5.6 kilometers (approximately 0.28 to 3.5 miles). The comet is traveling at an estimated speed of around 210,000 kilometers per hour (about 130,000 mph).
The increased activity of 3I/ATLAS as it nears the Sun is expected to yield valuable data on the composition and dynamics of interstellar comets. These upcoming observations by ESA's spacecraft are anticipated to significantly advance our understanding of these rare cosmic travelers and the formation of planetary systems beyond our own.