By Kenneth Chang For

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NYT News ServiceA still image of the comet 3I/ATLAS captured by the European Space Agency’s ExoMars Trace Gas Orbiter, provided by the European Space Agency. (European Space Agency via The New York Times) — NO SALES; FOR EDITORIAL USE ONLY WITH COMET MARS IMAGES BY KENNETH CHANG FOR OCT. 7, 2025. ALL OTHER USE PROHIBITED. —

Scientists have detected signs of water on the interstellar comet 3I/ATLAS, only the third known object to enter our solar system from another star system. Two spacecraft orbiting Mars, the ExoMars Trace Gas Orbiter (TGO) and Mars Express, recently captured the comet’s closest approach to the Red Planet, offering humanity its best view yet of the mysterious traveler. During its flyby on October 3, the comet came within 18.6 million miles (30 million kilometers) of Mars. While ESA’s Mars Express could not capture the faint object, the ExoMars TGO succeeded, recording a sequence of images showing the comet streaking across space at an estimated 130,000 mph (210,000 km/h). Meanwhile, astronomers at Auburn University, using NASA’s Neil Gehrels Swift Observatory, a research team led by Zexi Xing detected the ultraviolet signature of hydroxyl, a chemical byproduct of water vapor, confirming that the interstellar visitor carries traces of water.How much water is 3I/ATLAS releasing?Scientists calculated hydroxyl emissions within a 10-arcsecond radius and estimated 2.2 × 10³⁰ molecules in July and 4.2 × 10³⁰ in mid-August, confirming a dramatic increase in water production, which means that the comet’s coma ejects around 40 kilograms of water every second (1.36 × 10²⁷ molecules per second).They also found that at least 8 per cent of the comet’s surface, roughly 7.8 square kilometers, must be actively releasing vapor, compared to the 3–5% activity seen in most comets.This unusually high rate suggests that 3I/ATLAS may have an ice-rich surface or be expelling volatile dust grains that continue to release water after leaving the nucleus, marking it as one of the most active interstellar visitors ever recorded.Why are these findings relevant?This water activity was observed when 3I/ATLAS was nearly three times farther from the Sun than Earth, a region typically too cold for water to vaporize. This suggests that the comet’s water is released through tiny ice grains ejected into space, where even weak sunlight is enough to sublimate them, a rare behavior seen in only a few known comets.Live Events3I/ATLAS can solve secrets of life’s journey and planet formationThe discovery of water on interstellar comet 3I/ATLAS can open a new window for scientists to a rare glimpse into how planets and life-building materials might form and travel across the galaxy. Researchers say comets like 3I/ATLAS could act as ‘delivery vehicles,’ carrying water and organic molecules between star systems, potentially spreading the ingredients of life across the universe, explains thebrighterside.What makes this comet even more intriguing is its unique chemical makeup. Unlike typical comets, 3I/ATLAS is water-rich but low in cyanogen (CN), suggesting it may have formed in a carbon-poor region near a young, metal-deficient star.As lead researcher Zexi Xing explained, “Each interstellar comet that has come by so far has been a surprise. ‘Oumuamua was dehydrated, Borisov was carbon monoxide-rich, and now ATLAS is losing water at a distance where we didn’t expect it. Each one is rewriting what we thought we knew about the formation of planets and comets around stars,’ quotes the outlet.Add as a Reliable and Trusted News Source Add Now!
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