When a celestial body from another star system enters our solar neighborhood, it captures the attention of astronomers. However, when that body, known as comet 3I/ATLAS, begins ejecting enough water to fill 70 Olympic swimming pools daily, it sparks a frenzy of scientific inquiry.
Discovered last summer, 3I/ATLAS made headlines as it approached the sun. The European Space Agency's Jupiter Icy Moons Explorer (Juice), originally designed for a different mission, redirected its instruments to observe this remarkable comet.
The data, which arrived on Earth in February 2026, unveiled a frozen artifact from over 10 billion years ago--predating our Solar System, which is only 4.5 billion years old. This unique information offers scientists a rare glimpse into the processes of planetary formation around distant stars.
A Cosmic Water Fountain
Water is essential for life, making its presence on extraterrestrial bodies a point of significant interest. Normally, comets remain dormant until they approach a star, where heat causes their ice to sublimate and form tails. However, 3I/ATLAS exhibited activity long before reaching the sun, leaking water at an astonishing rate of 40 kilograms per second even while still far from our planet.
This early outflow was likened to a fire hydrant, indicating a fragile structure that releases easily vaporized ice into a vast gaseous halo. "When we detect water from an interstellar comet, we're reading a note from another planetary system," explained Dennis Bodewits, a physicist from Auburn University involved in the study.
Strategic Observations
As 3I/ATLAS neared its closest point to the sun in November 2025, Earth-based telescopes struggled to capture its movement due to solar glare. Fortunately, the Juice spacecraft was perfectly positioned to gather data during this crucial period. Mission scientists took a calculated risk by activating five of Juice's scientific instruments, successfully capturing a wealth of information.
"3I/ATLAS is an unexpected visitor, and its arrival provided a unique opportunity for data collection," remarked Olivier Witasse, ESA Juice Project Scientist. The gamble proved fruitful, offering insights that will enhance our understanding of comets and their behavior.
Rivers of Water in Space
Upon receiving data from Juice, researchers were astonished by the volume of water expelled by the comet. The Moons And Jupiter Imaging Spectrometer (MAJIS) detected infrared emissions of water vapor and carbon dioxide, estimating an outflow of approximately two tons per second--equivalent to 70 Olympic swimming pools of water vapor daily.
Interestingly, much of this water is not venting directly from the comet's solid nucleus but instead boiling off from a cloud of icy dust on the sunlit side.
A Unique Chemical Signature
The water composition in 3I/ATLAS also differs from that found in our solar system. By analyzing the ratios of light to semi-heavy water, scientists have deduced that this comet originated in an extremely cold, ancient environment, shaped by intense radiation from young stars.
"Every interstellar comet has been a surprise," noted Zexi Xing, an Auburn University researcher. "3I/ATLAS is rewriting our understanding of how comets and planets form around stars."
Future Implications
As the Juice spacecraft prepares for its journey to Jupiter, the data collected from 3I/ATLAS will significantly enhance our understanding of icy bodies in space. "We are excited about the potential revelations regarding Jupiter and its moons in the coming decade," said co-Project Scientist Claire Vallat. This extraordinary comet encounter may pave the way for groundbreaking discoveries about the origins of water and life throughout the universe.