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New evidence confirms that the interstellar comet 3I/ATLAS is significantly older than our own solar system. Scientists have also found clues indicating that this object formed on the far edges of the protoplanetary disk around its parent star billions of years ago. This discovery provides a rare window into the early history of another star system.
Earlier this year, researchers led by Martin Cordiner from NASA’s Goddard Space Flight Center announced findings based on data from the James Webb Space Telescope (JWST). The data suggested that 3I/ATLAS is between 10 and 12 billion years old. This estimate was derived from the ratios of carbon and deuterium isotopes found in the comet. These numbers are striking because our solar system is only 4.6 billion years old. This makes 3I/ATLAS more than twice as old as the Sun and its planets.
New results from the Ultraviolet and Visual Echelle Spectrograph (UVES) on the European Southern Observatory’s Very Large Telescope support the JWST observations. The UVES measurements confirmed the carbon isotope findings. Additionally, the telescope introduced new measurements of nitrogen isotopes. These new measurements lead to fascinating conclusions about the comet’s life story.
To understand these findings, it is important to know what isotopes are. Isotopes are different versions of the same atomic element. They have the same number of protons but different numbers of neutrons. For example, carbon-12 has six protons and six neutrons. Carbon-13 also has six protons, but it has seven neutrons. Similarly, nitrogen-14 has seven protons and seven neutrons, while nitrogen-15 has seven protons and eight neutrons.
These isotopes form through slightly different processes. They form at different times and in different places throughout the galaxy. The ratio of these isotopes in the gases released by 3I/ATLAS can tell us a great deal about its origin. As the comet approached the Sun, it grew warmer. This heat caused gases to escape into its coma and tail. Analyzing the mix of isotopes in these gases allows scientists to trace the comet’s history.
This object is essentially a fossil. It preserves the conditions of planetary formation that occurred far away from our solar system. Astronomer Cyrielle Opitom of the University of Edinburgh explained this concept. She stated that interstellar objects like 3I/ATLAS are "sort of fossils from a planetary formation process that happened very far away, but we get the chance to study from much closer." This proximity allows us to study the chemistry of other worlds in detail.
Opitom led the team that observed 3I/ATLAS using the Very Large Telescope. Her team found that the ratio of carbon-12 to carbon-13 in the comet is higher than the ratio found in comets within our solar system. This ratio is also higher than what is found in the local interstellar medium. Carbon-13 is produced in larger amounts over time, primarily in red giant stars. Therefore, a high amount of carbon-12 compared to carbon-13 indicates that 3I/ATLAS was born long ago. It formed before carbon-13 had a chance to build up in abundance across the galaxy. This finding strongly supports the carbon isotope measurements previously made by JWST.
The team, which was co-led by Jean Manfroid and Damien Hutsemékers from the University of Liège in Belgium, also measured nitrogen isotopes. They found a ratio of nitrogen-14 to nitrogen-15 that is more than twice as large as the value measured in comets native to our solar system. This specific ratio is typical of the outer edge of planet-forming discs around young stars. This implies that 3I/ATLAS formed very far from its parent star. It likely formed in a region similar to the Kuiper Belt in our own solar system.
Aravind Krishnakumar, a team member from the University of Liège, highlighted the uniqueness of these findings. He noted, "Unlike comets from our solar system, this interstellar visitor carries unusually high carbon and nitrogen isotopic ratios." These unusual ratios provide critical data points for understanding different planetary environments.
These results offer clues about how 3I/ATLAS came to wander the space lanes alone for billions of years. Models of planetary systems indicate that migrating giant planets can kick small bodies into interstellar space. However, the location of 3I/ATLAS’s birth far from the planetary zone suggests a different origin story. It is quite possible that the comet was snatched from its parent star by the gravity of a passing star. This gravitational interaction then hurled it into deep space. This mechanism explains how it could have been ejected from the outer regions of its system.
The JWST had previously shown that 3I/ATLAS is rich in carbon monoxide and carbon dioxide relative to water. It also contains unexpectedly high abundances of nickel and iron. Furthermore, it has a very high abundance of methanol relative to hydrogen cyanide. All of these chemical traits tell us that 3I/ATLAS formed in an environment with conditions and chemistry that are notably different from our own solar system. It is a true alien visitor in terms of its composition.
Unfortunately, similar measurements were not possible with the other two known interstellar objects. 1I/'Oumuamua was not seen to outgas, meaning we could not analyze its coma. Object 2I/Borisov was too faint to provide detailed chemical data. However, 3I/ATLAS is a tantalizing indication of what future discoveries might reveal. Studies of more interstellar objects entering our solar system will likely teach us about planet-forming conditions across both space and time in the Milky Way galaxy.
Rosemary Dorsey, an astronomer from the University of Helsinki in Finland, summarized the significance of this discovery. She concluded, "3I/ATLAS is a really exciting opportunity to probe the composition of another planetary system, one that formed long before our Sun and solar system even existed." This object allows us to look back at a time before our own planetary system was born.
The findings were published on July 6 in the journal Nature Astronomy. This publication makes the data available to the global scientific community. Researchers worldwide can now analyze these results to refine models of galaxy evolution. Each new interstellar object offers a piece of a much larger puzzle. 3I/ATLAS provides one of the clearest and most detailed pieces yet.