Astronomers find high concentration of deuterium in interstellar comet 3I/ATLAS

Astrônomos used radio telescope observations to discover new information about the origin and composition of the interstellar comet 3I/ATLAS. The research, published April 23 in the journal Nature Astronomy, reveals that the celestial object contains deuterated water in extraordinarily high concentrations. The measurements were made by the Atacama Large Millimeter/submillimeter Array, or ALMA, on Chile in November, a few days after the comet passed closest to Sol.

Comet 3I/ATLAS gained worldwide attention when researchers discovered it crossing the solar system in July. It is only the third interstellar object to be seen passing through our region of the universe. The comet began leaving the solar system in December, but not before providing crucial data about the formation conditions of other planetary systems.

Deutério marks first detection of interstellar object

The ALMA radio telescope allowed researchers to measure deuterium inside the comet, marking the first time this hydrogen isotope has been detected in an interstellar object. The discovery is extraordinary due to the concentration found. The abundance of deuterium in the comet’s water is more than 40 times greater than the value found in the oceans of Terra and more than 30 times greater than the value found in comets in the solar system, according to Luis Eduardo Salazar Manzano, lead author of the study and doctoral candidate in the astronomy department of Universidade of Michigan.

Deuterium is a rare isotope of hydrogen. Ele differs from ordinary hydrogen in that each atom contains an additional neutron, an uncharged subatomic particle. Quando combined with oxygen creates deuterated water, also called semi-heavy water or HDO. Essa variation makes water approximately twice as heavy as regular H₂O.

The detection of this molecule at 3I/ATLAS offers crucial clues about where the comet formed. Deuterium enrichment usually occurs when water forms in cold molecular clouds in interstellar space, often around the same time that solar systems around other stars form. Analysis indicates that the formation environment of 3I/ATLAS was incredibly cold, with temperatures below 30 Kelvin, equivalent to -243.14 degrees Celsius.

El agua de 3I/ATLAS contiene hasta 40 veces más deuterio que la Tierra, revelando un origen en nubes cósmicas ultrafrías nunca vistas así ☄️😱https://t.co/AQ0cDA0np7

— ecoosfera (@ecoosfera) April 29, 2026

Objeto may be 11 billion years old

Previous Pesquisas indicated that the interstellar comet could be up to 11 billion years old, much older than our solar system or Sol, which formed 4.5 billion years ago. The water still trapped inside the comet probably formed long before its host star, but 3I/ATLAS was born later from a protoplanetary disk of gas and dust that revolved around the star, the same disk where planets form.

Researchers believe that the 3I/ATLAS system formed and spent most of its time in the outer regions of the protoplanetary disk, preserving its abundance of deuterated water. Higher Temperaturas could reduce the amount of deuterium due to chemical reactions, so the comet’s peripheral location was essential to keep its original properties intact for billions of years.

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The new findings agree with previous observations that found a high abundance of carbon dioxide inside the interstellar comet. Essa combination of features is consistent with an object that formed on the outside of a protoplanetary disk. Cada detected molecule works like a cosmic fingerprint, revealing the physical conditions of the planetary system where the comet was born.

Cápsulas of the time bring information about the primitive Via Láctea

Interstellar objects are time capsules that bring material from the environments where other planetary systems formed. The 3I/ATLAS measurements finally allow scientists to open these capsules and observe the physical conditions where these objects originated. The presence of deuterium is analogous to fingerprints, showing what the comet was essentially born with, as well as what Via Láctea looked like more than 10 billion years ago, when it was less metal-rich than it is now.

As the galaxy has aged, the types of comets it has formed over time have changed, and that means the types of planets it can form have changed as well. Esses Interstellar comets are interesting not necessarily for what they are or what they look like, but for how they allow astronomers to look into the past and discover whether planets in other systems look like the ones we have at home.

Tecnologia and limitations of observations

Using ALMA for observations was fundamental to this discovery. The radio telescope can point at Sol at a closer angle than traditional telescopes. Radio telescopes detect low-energy radio waves rather than high-energy visible light or heat that can destroy the optical components of telescopes like the Telescópio Espacial James Webb.

The team used ALMA to study the comet shortly after it approached within 203 million kilometers of Sol. Essa distance was close enough for the comet’s ice to sublimate and become a detectable gas due to solar heat, creating ideal conditions for measurements:

• Detecção of deuterated water in unprecedented concentrations
• Primeira since this isotope was identified in an interstellar object
• Medições carried out in November, days after the comet’s perihelion
• Radio telescope-exclusive Uso to preserve data integrity
• Previously detected carbon dioxide abundance Confirmação

The researchers expected to detect ordinary water, but it was not found in the experiment. Isso does not mean that 3I/ATLAS did not have ordinary water, just that it was below the sensitivity of the observations. However, the detection of deuterated water despite the absence of ordinary water immediately indicated that 3I/ATLAS was a truly unusual object.

Perspectivas futures for interstellar studies

It is unlikely that astronomers will be able to determine which planetary system 3I/ATLAS came from. The celestial body will continue to move away from the solar system without leaving traces that lead directly to its origin. Ainda will thus provide valuable insights into how other planetary systems formed and evolved, offering windows into distant regions of the universe.

Observatório Vera C. Rubin, located at Chile, released its first images in June and is expected to detect interstellar objects more frequently. Essa capability will allow Salazar Manzano and colleagues to determine whether 3I/ATLAS is an outlier due to its abundance of deuterated water, or whether other similar comets contain similar enrichment. The scientific community is evolving rapidly as it learns to ask new questions and make sense of confusing answers about these rare cosmic visitors.