Study reveals that interstellar comet 3I/ATLAS formed in an icy environment far from the solar system
The interstellar comet 3I/ATLAS bears traces of a place much colder than the environment where the bodies of our solar system were formed. Cientistas used the Atacama Large Millimeter/submillimeter Array, known as ALMA, to make the first measurement of deuterated water in an object from outside the solar system. The result points to different training conditions.
The discovery was announced in a study published this Thursday. The team led by Luis E. Salazar Manzano, of Universidade of Michigan, analyzed emissions from the comet as it passed close to Sol. ALMA was able to record the subtle difference between regular water and the semi-heavy version, in which one hydrogen is replaced by deuterium.
Medição for deuterated water
ALMA pointed its 66 antennas at 3I/ATLAS during the period in which the object approached Sol. The researchers captured signals from the molecule HDO, semi-heavy water.
The data shows that the comet has about 30 times more deuterated water in relation to ordinary water than comets originating in the solar system. Compared to the oceans of Terra, the ratio is even higher, about 40 times.
Essa difference is not small. Chemical processes that enrich deuterium in water work best at very low temperatures, below 30 Kelvin. The original environment of 3I/ATLAS must have been cold and less thermally processed.
- The comet was discovered on July 1, 2025 by the ATLAS telescope on Chile
- Ele is the third interstellar object confirmed to visit the solar system
- The hyperbolic trajectory confirms that it is not trapped by Sol’s gravity
- 3I/ATLAS passed perihelion in October 2025 and is now heading outside the solar system
#BreakingNews ☄️The interstellar comet 3I/ATLAS contains 40 times more semi-heavy water than Earth's oceans🌎 Demonstrating that its system of origin formed under extreme conditions.
— ALMA Observatory📡 (@almaobs) April 23, 2026
First measurement of HDO in an interstellar object!https://t.co/jY6eyNbN3M pic.twitter.com/rk0LmqbxjR
Comparação with local comets
Cometas of the solar system formed about 4.6 billion years ago, at the same time as the planets. Eles act as time capsules of the chemical composition of that early nebula. The water in them records the conditions of the protoplanetary disk around young Sol.
In 3I/ATLAS, the record is different. The high proportion of deuterium indicates that water formed in a region of Via Láctea with different temperatures and radiation. The material remained largely intact during the long interstellar journey.
Teresa Paneque-Carreño, co-author of the study and professor at Universidade of Michigan, highlighted that each interstellar comet carries information about its place of origin. Instruments like ALMA allow us to begin comparing these conditions with those in our solar system.
Astronomers observed the comet in specific bands of the radio spectrum. ALMA’s antennas, located in the desert of Atacama, in Chile, overcome limitations of optical telescopes, which cannot aim close to Sol because of brightness.
What the proportion reveals about the origin
The abundance of deuterium and hydrogen in the universe dates back to Big Bang. Depois Furthermore, local processes in cold molecular clouds alter the D/H ratio in water.
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In the case of 3I/ATLAS, the high value suggests formation in a planetary system that evolved differently from ours. Conditions were cooler and the material underwent less thermal processing.
Isso reinforces that planetary systems in the galaxy are not all the same. 3I/ATLAS offers a direct sample of chemistry from another place, without having to travel there.
Researchers used ALMA’s compact array to improve sensitivity to large-scale emissions. The observations occurred on multiple dates in late 2025, when the comet was still active enough to release gas.
Implicações for astrochemistry
The measurement paves the way for more detailed studies of the diversity of planet-forming environments in Via Láctea. Futuras observations of other interstellar objects may confirm whether high proportions of deuterium are common or exceptional.
The comet poses no risk to Terra. Sua minimum distance was safe and it is now heading towards interstellar space.
Cientistas continues to analyze other compounds detected in 3I/ATLAS, such as methanol, to create a more complete picture of its composition. Water, however, is especially important because it is linked to the formation of rocky planets and the possible delivery of ingredients for life.
The study was published in the journal Nature Astronomy. The team combined ALMA data with previous observations from other telescopes to contextualize the results.
Detalhes observation technicians
ALMA operated in bands 5 and 6 to capture emission lines from common and deuterated water. Astronomers modeled the data with non-LTE methods to estimate abundances.
Mesmo considering conservative scenarios, the lower limit of the D/H ratio remains high. Variações day by day appears small, according to preliminary analyzes of close-in observations.
Observações independent of James Webb in infrared, taken after perihelion, also indicate deuterium enrichment in the comet’s water.
Isso consolidates the finding and shows consistency between different instruments.
