Cosmic origin: Did comets play a role in shaping Earth? Nasa discovers hydrogen on ‘Devil comet’ formed water

Scientists have uncovered groundbreaking evidence that Earth's water may have originated from comets, following a new study of Comet 12P/Pons-Brooks, nicknamed the "devil comet”. The research, published in August 2025 in Nature’s astronomy, revealed that the water vapor detected in this Halley-type comet has an almost identical chemical composition to Earth's oceans, providing the strongest evidence yet for the theory that comets delivered water to our planet.Comet 12P/Pons-Brooks, approximately the size of Mount Everest, made its first close approach to Earth since 1954 during the total solar eclipse in April 2025. The comet follows a 71-year orbit around the Sun and belongs to a group of ancient Halley-type comets that contain primordial material from the solar system's formation.Using the Atacama Large Millimeter/submillimeter Array in Chile and Nasa's Infrared Telescope Facility in Hawaii, researchers measured the deuterium-to-hydrogen ratio in the comet's water vapor. This ratio serves as a chemical signature that distinguishes water found on different celestial bodies.Scientists employed a breakthrough method to map both regular water and heavy water within the comet's coma, enabling them to confirm the water's origin from deep within the comet's nucleus."By mapping both H₂O and HDO, we can tell if these gases are coming from the frozen ices within the solid body of the nucleus, rather than forming from chemistry or other processes in the gas coma," said Nasa's Stefanie Milam, who co-authored the study."This is the strongest evidence to date supporting the idea that comets could have helped make our planet habitable," stated Nasa astrophysicist Martin Cordiner, who led the study.The discovery addresses a long-standing mystery about Earth's formation. Scientists believe Earth initially formed as a predominantly dry planet, with its high temperatures preventing water retention. The theory suggested that water arrived later through impacts from icy bodies like comets or asteroids during Earth's early evolution.Previous data had not supported this theory, as no comet had shown a close enough match in water composition until the analysis of 12P/Pons-Brooks. The comet's water signature presents one of the strongest matches ever recorded between cometary and terrestrial water.The findings suggest that Halley-type comets may have played a more significant role in creating Earth's environment than previously understood. This discovery has implications for future space missions, including the European Space Agency's Comet Interceptor and Nasa's proposed CAESAR project, which aims to return comet samples to Earth.The research indicates that these ancient comets may have not only delivered water but also potentially brought organic compounds that created conditions suitable for life on early Earth. The study of specific comet classes with matching deuterium-to-hydrogen ratios could provide further answers about Earth's origins and the formation of our solar system.