Organic Molecules Detected on Interstellar Comet 3I/ATLAS
NASA’s SPHEREx space telescope has confirmed the presence of complex organic molecules on the interstellar comet 3I/ATLAS. This discovery stems from detailed infrared observations conducted in December 2025, shortly after the comet emerged from behind the Sun.
According to data analyzed by SPHEREx, the instrument recorded data across 102 infrared wavelengths. Spectral analysis revealed the presence of water vapor, carbon dioxide, dust, and complex organic molecules – key components in the formation of the building blocks of life.
A Third Interstellar Visitor
3I/ATLAS is known as the third confirmed interstellar object to enter our solar system, following ʻOumuamua and 2I/Borisov. The comet was first detected in July 2025 by the ATLAS monitoring system.
Its trajectory is hyperbolic, indicating that it will pass through our solar system only once before returning to interstellar space. This limited timeframe presents a unique opportunity for scientists to study its characteristics.
Increased Activity After Perihelion
Comet 3I/ATLAS reached its closest approach to the Sun (perihelion) in October 2025, at a distance of approximately 1.4 astronomical units. This proximity triggered intense activity, including outbursts of gas and dust from its surface.
Follow-up observations in December showed a significant increase in brightness. Material ejected from the comet’s nucleus formed a coma, a luminous gas envelope that can extend hundreds of thousands of kilometers. In some instances, the carbon dioxide envelope exceeded 348,000 kilometers in extent.
The detected water vapor indicates the sublimation of ice due to exposure to the Sun’s heat. Released dust reflects infrared radiation, while complex organic molecules appear in specific spectral bands.
Unveiling Ancient Material
The organic molecules discovered are complex carbon chains similar to precursors to biological material. These compounds are considered fundamental building blocks involved in the chemical processes leading to life.
This material had been frozen within the interstellar environment for potentially billions of years. As the comet passes near the Sun, heat triggers the release of these long-stored elements, providing a rare opportunity for scientists to study them directly.
Comparisons with comets originating from within our solar system suggest differences in the proportions of ices and material content. Interstellar objects like 3I/ATLAS are believed to retain a more primitive composition.
The detection of these organic molecules doesn’t indicate the presence of life, but rather highlights the potential for the delivery of prebiotic materials throughout the galaxy. These molecules are the chemical foundations upon which life *could* be built, though many other factors are required for life to actually emerge.
SPHEREx’s infrared capabilities are particularly well-suited to this type of observation. By measuring the infrared light emitted by the comet, scientists can determine the composition of the coma and nucleus without directly sampling the material. This is crucial, as physically visiting an interstellar object is currently beyond our technological capabilities.
The mission’s observations also provide insights into the processes that occur when comets are heated by the Sun. Sublimation, the direct transition from solid ice to gas, is a key driver of cometary activity. Understanding this process is essential for interpreting observations of comets throughout the solar system and beyond.
Further analysis of the SPHEREx data is expected to reveal even more details about the composition and origin of 3I/ATLAS. This research contributes to a broader understanding of the chemical diversity of interstellar space and the potential for the delivery of prebiotic molecules to planetary systems.
The study lead, Carey Lisse of Johns Hopkins Applied Physics Laboratory, noted the significant brightening of the comet in December 2025, attributing it to the substantial release of water ice and carbon-rich material. This outburst, he explained, is a consequence of the comet’s journey from deep space and subsequent heating by the Sun.
The findings from SPHEREx add to a growing body of evidence suggesting that comets may have played a role in delivering the building blocks of life to early Earth. While the exact mechanisms remain a subject of ongoing research, the detection of organic molecules on interstellar comets strengthens the hypothesis that these icy bodies could have seeded our planet with the ingredients necessary for life to arise.
