It is believed that the comet 3I/ATLAS, the third known interstellar visitor to cross the Solar System, may have formed in an ancient icy planetary system about 12 billion years ago in an extremely cold environment and has a unique chemical composition.
New data supporting these assumptions were obtained from observations made by the James Webb space telescope and the ALMA observatory. These observations formed the basis of a study published in the journal Nature, led by NASA’s Goddard Space Flight Center (USA).
The comet 3I/ATLAS was discovered in July 2025 and last November made its closest approach to Earth before continuing its journey beyond the Solar System. When the comet began moving away from the Sun in December, astronomers took the opportunity to study its chemical composition, which allowed them to understand the environment in which it formed. Measuring isotope ratios (different versions of chemical elements) can provide clues about the physical and chemical conditions of its formation.
Mysteries of the comet’s formation
The ratios of hydrogen isotopes provide information about the temperature and radiation of the environment where 3I/ATLAS formed, while the ratios of carbon isotopes can help determine the object’s origin from an interstellar gas cloud. The comet’s water contains 10 times more deuterium (a hydrogen isotope) than other known comets, suggesting its possible origin from a very cold system in a much earlier epoch in the history of our galaxy.
Astronomers suggest that 3I/ATLAS may have formed in an icy cloud at a temperature of about -243 degrees Celsius, approximately 10-12 billion years ago. The carbon ratio exceeds typical values observed in the Solar System, as well as in neighboring interstellar clouds and protoplanetary disks, indicating a very ancient origin, possibly from an ancient primordial planetary system.
Previous studies also pointed to the possibility that the comet may have icy volcanoes that erupt, a phenomenon known as cryovolcanism. This would explain the increase in its brightness during its closest approach to the Sun, which occurred in October.
Source: Clarín