In a breakthrough discovery, researchers have found that the water on the so-called “Devil Comet” is strikingly similar to the water on Earth, offering powerful support for the theory that comets may have played a key role in delivering the building blocks of life to our planet.
The findings, published on August 8 in Nature Astronomy, come from an international team led by NASA molecular astrophysicist Martin Cordiner. Using advanced observations, the researchers determined that comet 12P/Pons-Brooks, a Halley-type comet, contains water with an isotopic signature nearly identical to Earth’s.
“Our new results provide the strongest evidence yet that at least some Halley-type comets carried water with the same isotopic fingerprint as Earth, supporting the idea that comets could have helped make our planet habitable,” Cordiner said.
The team relied on the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and NASA’s Infrared Telescope Facility (IRTF) in Hawaii to examine the comet, which orbits the Sun every 71 years. By measuring the ratio of deuterium, or “heavy” hydrogen, to normal hydrogen — a key chemical marker known as the D/H ratio — they discovered that 12P/Pons-Brooks’ water is “virtually indistinguishable” from Earth’s.
This finding is significant because earlier studies of Halley-type comets showed water with different D/H ratios, creating doubt about their role in Earth’s watery origins. The new data, however, revives the possibility that comets were central in seeding our young planet with water billions of years ago.
The ALMA observations also marked the first time scientists have been able to map water within a comet in such fine detail. By studying both ordinary water (H₂O) and its heavier variant (HDO, which contains deuterium), the researchers confirmed that the gases were released directly from frozen ices in the comet’s nucleus, rather than forming later through chemical processes.
“By mapping both H₂O and HDO in the comet’s coma, we can confirm that the water is primordial — preserved from the early solar system,” said Stefanie Milam, NASA project scientist and study co-author.
The discovery not only deepens understanding of comets like 12P/Pons-Brooks but also strengthens the broader case that Earth’s life-supporting environment may have been shaped by icy messengers from the depths of space.