NASA Observes Interstellar Comet 3I/ATLAS, Unveiling Compositional Secrets

NASA missions have extensively observed interstellar comet 3I/ATLAS, the third such object identified to visit Earth's solar system. The observations provided insights into its composition and trajectory as it exits the solar system permanently. Data collected from various missions, including the Transiting Exoplanet Survey Satellite (TESS) and the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx), will be preserved in NASA's public data archives.

Discovery and Trajectory

Comet 3I/ATLAS was first identified on July 1, 2025, by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile. Retrospective analysis of existing data later revealed earlier observations, with NASA's TESS having captured the comet in May 2025. These early observations enabled astronomers to more effectively track the comet's path.

After passing the Sun in late October 2025, 3I/ATLAS came within approximately 168 million miles (270 million kilometers) of Earth in December 2025. The comet is currently traveling toward Jupiter, where NASA’s Juno spacecraft is expected to conduct further studies before 3I/ATLAS exits the solar system permanently.

Observational Campaigns and Key Findings

Over a dozen NASA science missions contributed to the observation campaign for 3I/ATLAS.

TESS Observations

NASA's TESS observed 3I/ATLAS from January 15 to January 22, (presumably 2026, following its 2025 close approach), as it moved out of the solar system. Its wide field of view recorded the comet as a bright, fast-moving object displaying a faint tail against a star field. Data from TESS showed the comet's apparent magnitude at approximately 11.5, making it observable with telescopes.

Daniel Muthukrishna of the Massachusetts Institute of Technology (MIT) compiled a 28-hour video from TESS data, which included a time gap from January 15 to January 18 due to the spacecraft entering 'safe mode'. Researchers plan to use this data to analyze the comet's activity and rotation, providing information on its dust and gas shedding rate and the speed of its core's spin.

SPHEREx and Organic Molecule Detection

NASA’s SPHEREx space telescope observed comet 3I/ATLAS from December 8 to 15, 2025, shortly after its launch in March 2025. These observations detected organic molecules, including methanol, cyanide, and methane, emanating from the comet. While these molecules are considered fundamental for biological processes on Earth, NASA noted that their presence can also result from non-biological processes. These findings were published in the February issue of the Research Notes of the AAS, though the research is considered work in progress and has not yet undergone peer review.

Carey Lisse, an astronomer at Johns Hopkins Applied Physics Laboratory, noted that 3I/ATLAS was erupting into space and releasing carbon-rich material after its close flyby of the Sun, consistent with comets releasing gases as ice sublimates near stars.

Compositional Insights

Scientists anticipated that 3I/ATLAS would exhibit different characteristics compared to comets originating within our solar system due to its interstellar origin. The extensive observation campaign provided insights into its composition. Researchers determined that the relative production rates of water, carbon dioxide, and carbon monoxide for 3I/ATLAS differed from those of typical comets. This finding was achieved by combining spectral data from NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) Mars orbiter with infrared observations from NASA’s James Webb Space Telescope and SPHEREx.

Scientific Significance and Data Accessibility

Comet 3I/ATLAS is the third interstellar visitor ever detected and is potentially the oldest comet observed. While some speculation suggested it could be an alien spacecraft, astronomers widely consider it a natural comet from another star system. One scientific theory suggests that comets may contribute to spreading the "seeds of life" across the cosmos.

Data from 3I/ATLAS is expected to advance understanding of interstellar objects, including their structure and composition.

Kevin Murphy, chief science data officer at NASA Headquarters, highlighted that NASA’s scientific data archives facilitate new discoveries, citing the early TESS observations of 3I/ATLAS as an example.

All collected observations are being preserved in NASA’s public data archives, aligning with the agency's commitment to open science. TESS data is publicly available through the Barbara A. Mikulski Archive of Space Telescopes (MAST), SPHEREx data via the NASA/IPAC Infrared Science Archive (IRSA), MAVEN data through the Planetary Data System, and Webb’s observations also in the MAST archive. This accessibility and standardization of data are intended to support future scientific inquiry.

Thomas Statler, lead scientist for Solar System Small Bodies at NASA Headquarters, emphasized the importance of preserving this data for future scientists to address emerging questions.

The first interstellar object, ‘Oumuamua, was detected in 2017. Scientists estimate that such objects pass through our solar system approximately once per year, and their discovery frequency is increasing with advanced telescopes. The data gathered from 3I/ATLAS is expected to serve as a significant reference for contextualizing and understanding interstellar comets in the future.