ESA to use Mars orbiters for 3I/ATLAS during solar conjunction

The European Space Agency is reassigning multiple spacecraft to observe 3I/ATLAS, a rare interstellar comet, as it passes near Mars on October 3, 2025, and becomes unobservable from Earth during a solar conjunction that runs from late September through December. With the comet expected to reach perihelion at the end of October and then make its closest approach to Earth in December, mission teams say spacecraft observations will be the only way to follow its most active phases.

Solar conjunction occurs when the Sun blocks Earth's line of sight to an object, making faint targets effectively invisible to ground telescopes. That blackout will coincide with the comet's period of greatest solar heating, when volatile ices sublimate and produce gas and dust. To bypass the glare, ESA will task its Mars Express and ExoMars Trace Gas Orbiter to pivot from Martian science to point their cameras and spectrometers at the passing object, which will come within roughly 30 million kilometres of Mars. NASA's Mars Reconnaissance Orbiter and rovers will also be available to assist, and several solar-orbiting observatories may contribute from vantage points away from Earth.