Comet 3I/ATLAS Spews Water Equivalent to 70 Olympic Pools Daily

In a remarkable feat of astronomical observation, scientists have detected that the interstellar comet 3I/ATLAS is shedding an astonishing amount of water into space. The European Space Agency's Jupiter Icy Moons Explorer (Juice) mission, while en route to Jupiter, captured data revealing the comet expels roughly two tons of water vapor per second. This equates to an astounding 70 Olympic-sized swimming pools of water ejected daily, a volume that offers an unprecedented opportunity for scientific study.

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Repeated detections of water vapor and carbon dioxide by MAJIS indicate that volatile ices buried beneath the surface were actively released into space shortly after perihelion passage.

The discovery, made using the Moons and Jupiter Imaging Spectrometer (MAJIS) and Jovis, Amorum ac Natorum Undique Scrutator (JANUS) instruments, provides a unique window into the composition of matter from beyond our solar system. As 3I/ATLAS approached the sun, its frozen core sublimated, releasing gases and forming its characteristic tail. The significant luminosity increase observed by Juice was far beyond initial expectations, prompting detailed analysis of the ejected volatiles like water vapor and carbon dioxide.

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From the data collected, we estimated an outflow from the comet's nucleus of about two tons per second, equivalent to approximately 70 Olympic swimming pools of water vapor ejected into space every day.

This observation was an unplanned bonus for the Juice mission, highlighting the serendipitous nature of space exploration. The comet's discovery on July 1, 2025, allowed the mission team a narrow window to gather data, which finally reached Earth in February 2026. The detailed analysis of the MAJIS data promises to deepen our understanding of cometary activity post-perihelion and the fundamental physical and chemical properties of materials formed around stars billions of years ago. The findings underscore the value of dedicated space missions, even when they deviate from their primary objectives, in expanding our cosmic knowledge.

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The MAJIS data will allow us to better understand the activity of this comet after perihelion and the physical and chemical properties of the materials formed around another star billions of years ago.