Scientists used the VLT telescope, located in Chile, to analyze in depth the composition of 3I/ATLAS. This interstellar comet, notable for its brightness, was even mistakenly identified as a possible alien probe during its passage.
By measuring specific chemical signatures, unprecedented observations of a comet that originated outside the boundaries of our Solar System indicated that 3I/ATLAS was likely born on the outskirts of an ancient star system. This discovery points to an origin significantly older than the Sun itself. The value of this research lies in the ability to closely study a cosmic “fossil” that offers clues about the formation of other planetary systems long before our own.
Celestial bodies classified as interstellar are those that form in orbit around a star other than our star star. On certain occasions, these objects penetrate our Solar System, and their presence is confirmed by analyzing their unusual trajectory and speed.
Cyrielle Opitom, from the University of Edinburgh, in the United Kingdom, highlighted the importance of these bodies, describing them as “fossils from a planetary formation process that took place very far away, but which we have the opportunity to study close to us.”
3I/ATLAS represents the third interstellar comet identified to date, coming after 1I/’Oumuamua and 2I/Borisov. Its detection occurred as it approached the Sun, and, despite its high speed, it remained for a prolonged period in our Solar System, which allowed astronomers to investigate it with a higher level of detail than its predecessors.
Analyzing isotopes: the composition of 3I/ATLAS
Unlike the challenges encountered in measuring the composition of the first two interstellar comets – in which one had no detectable gas and the other was too faint for viable observation – 3I/ATLAS allowed for a more in-depth study. Its intense brightness enabled astronomers to measure the comet’s isotopic quotients, that is, the relative proportions of the different forms of the same chemical element.
The spectral analysis revealed specific structures generated by 12C, a carbon isotope with six protons and six neutrons, and by 13C, which has six protons and seven neutrons in its composition.
Determining the age of comet 3I/ATLAS relative to the Sun
With the help of the UVES instrument, integrated into the VLT, the research team was able to measure the quotients of carbon and nitrogen isotopes found in the cyanide molecules present in the gas surrounding the comet. These quotients serve as accurate indicators of the origin of a comet, as they are highly sensitive to the physical conditions of the environment where it formed and tend to remain unchanged during its long journey through space.
Unexpected Interstellar Comet Composition Results
Aravind Krishnakumar, a researcher at the University of Liège in Belgium, noted that, “unlike comets in our Solar System, this interstellar visitor has unexpectedly high isotopic ratios of carbon and nitrogen.”
Overall, the findings suggest that the comet likely formed at the edge of a disk of matter that orbited an ancient, low-metallicity star. This type of star is predominantly composed of hydrogen and helium, with a very small amount of elements heavier than helium. Cosmological theories indicate that these stars existed when the Universe was still young and, consequently, poorer in chemical elements than it is today.
Perspectives on ancient stellar and planetary formation
Given these data, the team of scientists hypothesizes that 3I/ATLAS had its origins around a star that was more than twice the age of the Sun. Rosemary Dorsey, from the University of Helsinki, Finland, highlighted that “3I/ATLAS gives us an excellent opportunity to investigate the composition of another planetary system, formed long before our Sun and the Solar System even existed.”
