A comet from beyond our solar system is giving astronomers a rare look at how alien planetary systems may form under conditions very different from those that shaped our own cosmic neighborhood.
The object, called 3I/ATLAS, was discovered less than a year ago as it traveled through our solar system. Although scientists still do not know exactly where it originated, new research led by the University of Michigan suggests the comet formed in an extremely cold region of space.
The study, published in Nature Astronomy, found that 3I/ATLAS contains unusually high levels of deuterium-rich water, often called “heavy water.” The project received support in part from NASA, the U.S. National Science Foundation, and Chile’s National Research and Development Agency.
“Our new observations show that the conditions that led to the formation of our solar system are much different from how planetary systems evolved in different parts of our galaxy,” said Luis Salazar Manzano, lead author of the study and a doctoral student in the U-M Department of Astronomy.
Heavy Water Found in Interstellar Comet
Water is made up of two hydrogen atoms and one oxygen atom, giving it the chemical formula H2O. In normal water, hydrogen atoms contain only a proton. But deuterium is a heavier version of hydrogen that contains both a proton and a neutron.
Researchers discovered that a surprisingly large portion of the comet’s water contains deuterium. Heavy water can also be found on Earth and in comets from our solar system, but the amount detected in 3I/ATLAS was far greater.
“The amount of deuterium with respect to ordinary hydrogen in water is higher than anything we’ve seen before in other planetary systems and planetary comets,” Salazar Manzano said.
According to the researchers, the ratio of deuterium in the comet’s water was about 30 times higher than the levels measured in any comet from our solar system. It was also roughly 40 times greater than the ratio found in Earth’s oceans.
Clues About an Alien Birthplace
Scientists can use these chemical ratios to understand the conditions present when comets and planets formed. By comparing the chemistry of 3I/ATLAS with objects in our solar system, researchers concluded the comet likely formed in a colder environment with lower radiation levels.
“This is proof that whatever the conditions were that led to the creation of our solar system are not ubiquitous throughout space,” said Teresa Paneque-Carreño, co-leader of the study and assistant professor of astronomy at U-M. “That may sound obvious, but it’s one of those things that you need to prove.”
The researchers explained that carrying out such a detailed study required several fortunate circumstances, beginning with the comet being discovered early enough for additional observations.
How Scientists Studied 3I/ATLAS
Following the discovery, Salazar Manzano and collaborators secured observing time at the MDM Observatory in Arizona, where they detected some of the earliest signs of gas being released from the comet (MDM stands for Michigan, Dartmouth, and the Massachusetts Institute of Technology, the observatory’s original partners).
Salazar Manzano later joined forces with Paneque-Carreño, who contributed expertise using the Atacama Large Millimeter/submillimeter Array, or ALMA, in Chile to study the comet’s chemical composition in greater detail.
ALMA is sensitive enough to distinguish ordinary water from deuterated water, allowing the researchers to calculate the ratio between the two forms. Scientists say this marks the first time this type of analysis has ever been successfully performed on an interstellar object.
“Being at the University of Michigan and having access to these facilities was the key to making this work possible,” Salazar Manzano said. “We were part of a team that was very talented and very experienced in multiple areas; all of us complemented each other, and that’s what allowed us to analyze and interpret these data sets.”
Future Interstellar Discoveries
The researchers say the study demonstrates that future interstellar objects could also be chemically analyzed, potentially offering new insights into how planetary systems form throughout the galaxy.
So far, astronomers have detected only three known interstellar objects passing through our solar system, including 3I/ATLAS. However, Paneque-Carreño said discoveries like these could become much more common as new observatories begin scanning the skies.
She also emphasized the importance of protecting dark night skies so astronomers can continue detecting faint objects from deep space.
“We need to be taking care of our night skies and keeping them clear and dark so we can detect these tiny and faint objects,” she said.
Reference: “Water D/H in 3I/ATLAS as a probe of formation conditions in another planetary system” by Luis E. Salazar Manzano, Teresa Paneque-Carreño, Martin A. Cordiner, Edwin A. Bergin, Hsing Wen Lin (林省文), Dariusz C. Lis, David W. Gerdes, Jennifer B. Bergner, Nicolas Biver, Dominique Bockelée-Morvan, Dennis Bodewits, Steven B. Charnley, Jacques Crovisier, Davide Farnocchia, Viviana V. Guzmán, Stefanie N. Milam, John W. Noonan, Anthony J. Remijan, Nathan X. Roth and John J. Tobin, 23 April 2026, Nature Astronomy.
DOI: 10.1038/s41550-026-02850-5
Additional funding for the research came from the Michigan Society of Fellows and the Heising-Simons Foundation. ALMA operates through a partnership involving the European Southern Observatory, the NSF, and Japan’s National Institutes of Nature Sciences in cooperation with the Republic of Chile.
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