
Scientists have found that comet 3I/ATLAS, which drew global scientific interest in 2025, is more than 10 billion years old and may preserve clues about the galaxy’s early history.
The discovery comes from a study published in Nature Astronomy in late April.
Rare Interstellar Visitor Passes Near Earth
Researchers say the comet formed in a region far beyond the solar system. It is only the third known interstellar object to travel through the area of space near Earth.
Scientists used the Atacama Large Millimeter/submillimeter Array telescope in Chile in November last year to study the comet as it moved close to the sun. Scientists expect it to exit the solar system by the end of 2025.
Using observations from the radio telescope, scientists discovered for the first time a hydrogen isotope in an object beyond Earth’s atmosphere.
Unusual Water Composition Found in Comet 3I/ATLAS
They said the data revealed that the amount of deuterium in the water of comet 3I/ATLAS is more than 40 times higher than that found in Earth’s oceans and over 30 times greater than levels measured in comets within the solar system.
This form of water, called deuterated water, differs from ordinary water, which contains two hydrogen atoms and one oxygen atom. In deuterated water, the hydrogen atoms contain an extra neutron, making the water heavier.
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The analysis of the environment where the comet formed showed that it was extremely cold — even colder than the solar system during its early development. Scientists estimate the temperature was around -243.14 degrees Celsius.
Researchers believe the comet originated in a protoplanetary disk made of gas and dust orbiting a star, the same type of system in which planets are created.
The radio telescope also played a key role in the study. It allowed scientists to detect particles when the comet made its closest pass to the sun, at a distance of 203 million kilometers. At that point, the ice inside the comet sublimated, releasing gases that could be observed.
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