NASA’s SPHEREx mission has detected complex organic molecules within the coma of interstellar comet 3I/ATLAS, a finding that offers new insights into the potential building blocks of life in the universe. The observations, made in December 2025 using infrared spectroscopy, reveal the presence of water vapor, carbon dioxide, dust, and a variety of organic compounds.
A Rare Interstellar Visitor
3I/ATLAS is only the third interstellar object confirmed to have entered our solar system, following ʻOumuamua and 2I/Borisov. Discovered in July 2025 by the Asteroid Terrestrial-impact Last Alert System (ATLAS), the comet’s hyperbolic trajectory indicates it will pass through our solar system only once before returning to interstellar space. This limited window of opportunity makes detailed study particularly valuable.
Brightening After Perihelion
The comet reached its closest approach to the Sun, known as perihelion, in October 2025, at a distance of approximately 1.4 astronomical units. This proximity triggered a significant increase in activity, characterized by outbursts of gas and dust from the comet’s surface. Subsequent observations in December revealed a substantial brightening of the comet, as material ejected from the nucleus formed a coma – a luminous gaseous envelope extending hundreds of thousands of kilometers. The carbon dioxide envelope was recorded as extending beyond 348,000 kilometers.
The detection of water vapor confirms the sublimation of ice due to solar heating. Dust reflects infrared radiation, while the identified organic molecules are detectable through specific spectral bands. SPHEREx’s ability to observe in 102 different infrared wavelengths was crucial to this detailed analysis.
Unveiling Ancient Materials
The organic molecules detected on 3I/ATLAS are complex carbon-based chains resembling precursors to biological compounds. These compounds are considered essential building blocks in the chemical processes leading to life. These materials are believed to have been frozen in the interstellar medium for billions of years. As the comet approaches the Sun, heat triggers the release of these stored elements, providing a unique opportunity for scientists to study them directly.
The research note published by SPHEREx scientists details the detection of specific organic molecules including methanol, cyanide, and methane. On Earth, these organic molecules are foundational for biological processes, though they can also be created through non-biological means.
SPHEREx’s Unique Capabilities
NASA’s Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) was designed for an all-sky survey, collecting data from over 450 million galaxies and 100 million stars in the Milky Way. The mission aims to explore the origins and evolution of the universe. However, the team took the opportunity to observe 3I/ATLAS as it emerged from behind the Sun, demonstrating the mission’s flexibility and observational power.
The comet’s brightening after its closest approach to the Sun was particularly noteworthy. According to Carey Lisse of Johns Hopkins Applied Physics Laboratory, the lead author of the research note, “Comet 3I/ATLAS was full-on erupting into space in December 2025, after its close flyby of the Sun, causing it to significantly brighten. Even water ice was quickly sublimating into gas in interplanetary space.” Lisse further explained that, given comets are roughly one-third water ice, the sublimation released a significant amount of new, carbon-rich material that had been locked within the ice.
Implications for Understanding the Early Universe
Comparing the composition of 3I/ATLAS to comets originating within our solar system suggests that interstellar objects like 3I/ATLAS retain a more primitive composition. This offers valuable clues about the conditions present in the early universe. The detection of these organic molecules provides further evidence that the ingredients for life may be widespread throughout the cosmos, potentially delivered to planetary systems via comets and other interstellar objects.
The data collected by SPHEREx will help scientists understand the composition of 3I/ATLAS and how its ices react to solar heating as it continues its journey through the outer solar system. The mission continues to gather data, and further analysis is expected to reveal even more about this fascinating interstellar visitor.
