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Comet 3I/ATLAS, the third confirmed interstellar visitor in the Solar System, draws astronomers’ attention after a study identifies water with deuterium content much higher than observed in local comets and Earth’s oceans, indicating possible formation in an extremely cold region with low radiation outside the solar neighborhood
3I/ATLAS, the third confirmed interstellar visitor ever detected in the solar system, exhibits an unusual water composition that points to a birth in an environment much colder than that associated with the formation of planets and comets near Earth. This conclusion comes from a new study led by researchers at the University of Michigan, published in the journal Nature Astronomy, which identified exceptionally high levels of deuterium in the comet’s water.
The object was detected less than a year ago as it traversed the solar system from a region far beyond it. Now, the analysis of its composition is beginning to reveal clues about the alien location where the comet formed and about planetary processes at work elsewhere in the galaxy.
The research received support from NASA, the U.S. National Science Foundation, and the Chilean National Agency for Research and Development. For scientists, the data indicates that the conditions that gave rise to our solar system are not replicated in the same way across all known planetary environments.
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3I/ATLAS reveals water with unusual deuterium content
The main discovery involves the water present in 3I/ATLAS, which contains a very high amount of deuterium. This isotope of hydrogen is heavier because it has one proton and one neutron, while common hydrogen has only one proton.
Common water molecules are formed by two hydrogen atoms and one oxygen atom, a combination represented by the formula H₂O. In some forms of water, part of the hydrogen is replaced by deuterium, creating what is known as heavy water.
Small amounts of this type of water exist on Earth and also in comets within the solar system. However, the levels found in 3I/ATLAS were much higher than those observed in objects known until now.
Luis Salazar Manzano, lead author of the study and a doctoral student in the Department of Astronomy at the University of Michigan, stated that the amount of deuterium relative to common hydrogen in the water is greater than any previous record in other planetary systems and planetary comets. The proportion measured in the comet was about 30 times higher than that found in comets in our solar system.
The difference is also significant when compared to Earth. The deuterium proportion in 3I/ATLAS was approximately 40 times higher than that recorded in Earth’s oceans.
Comet may have been born in a much colder region
Scientists use deuterium levels as a kind of chemical fingerprint. This measurement helps indicate the conditions present at the time celestial objects formed.
By comparing these proportions with those found in closer regions, the team concluded that 3I/ATLAS likely originated in a much colder area. The environment would also have had lower radiation levels than those associated with the formation of planets and comets in our solar system.
Salazar Manzano stated that the new observations show important differences between the conditions that led to the formation of the solar system and how planetary systems evolved in other regions of the galaxy. The analysis reinforces the idea that interstellar objects can carry chemical records of very distinct environments.
Teresa Paneque-Carreño, co-lead of the study and assistant professor of astronomy at the University of Michigan, stated that the discovery proves that the creation conditions of the solar system are not the same throughout space. For her, this difference may seem obvious, but it needs to be demonstrated through observations.
Observations began early and allowed for unprecedented analysis
The study was only possible because 3I/ATLAS was identified early enough to allow for a sequence of detailed observations. After the discovery, Salazar Manzano and his collaborators secured observation time at the MDM Observatory in Arizona.
At this observatory, the team detected some of the first signs of gas emissions from the comet. The acronym MDM refers to Michigan, Dartmouth, and the Massachusetts Institute of Technology, the original partners of the facility.
After this stage, Salazar Manzano began working with Paneque-Carreño, who brought experience in using the Atacama Large Millimeter/submillimeter Array, ALMA, in Chile. ALMA’s instruments have sufficient sensitivity to differentiate deuterated water from common water.
This capability allowed researchers to precisely measure the ratio between the two forms of water in 3I/ATLAS. The team states that this was the first time scientists were able to perform this type of water analysis on an interstellar object.
Salazar Manzano stated that being at the University of Michigan and having access to these facilities was fundamental to the work. He highlighted the participation of an experienced team in various areas, with complementary skills to analyze and interpret the data.
Discovery paves the way for new interstellar studies
The study of 3I/ATLAS also shows that astronomers will be able to chemically analyze other interstellar objects in the future. This possibility can broaden the understanding of how planetary systems form in different regions of the galaxy.
So far, only three known interstellar objects have been identified entering the solar system. Researchers expect this number to grow with the arrival of more advanced observatories, capable of scanning the skies with greater efficiency.
The detection of these visitors, however, depends on adequate observation conditions. Paneque-Carreño emphasized the importance of preserving dark night skies so that small and faint objects can be found.
The analysis of 3I/ATLAS reinforces the scientific value of these rare visitors. Each interstellar object that crosses the solar system can carry information from distant regions, formed under conditions different from those that shaped Earth’s vicinity.
With water much richer in deuterium than that found in local comets and Earth’s oceans, 3I/ATLAS became a chemical sample of a cold environment, dimly lit by radiation. For researchers, this visitor confirms that the galaxy harbors diverse planetary processes, still largely inaccessible to direct observation.
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