3I/ATLAS Archives

Top: coma maps of H2O, CO2, and CH4, computed as the molecular column density from a pixel-by-pixel retrieval analysis for Observations 6, 15, and 6, respectively. The sunward and target velocity directions are denoted by the white arrows. The target centroids, computed as the photocenter in the median-stacked images (Figure 1), are marked with the black points. For H2O and CO2, the white contours correspond to emission levels of 50% and 20% relative to the maximum value and illustrate the slight antisunward extension of the respective comae. The contours are omitted in the CH4 panel, due to the poorer signal-to-noise ratio of the data. Bottom: corresponding median-stacked images across the continuum wavelengths within each fluorescence region. The H2O coma map shows a significant enhancement in the emission level at large nucleocentric distances relative to the dust continuum, indicating extended H2O production within the coma. -- The Astrophysical Journal Letters

Astrochemistry, Astronomy & Telescopes, Biogeochemical Cycles & Geobiology, Biophysics, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Press Release

Webb Detects Methane on Interstellar Comet 3I/ATLAS

by Keith CowingJune 2, 2026June 2, 2026

NASA’s James Webb Space Telescope has collected its first mid-infrared chemical fingerprint of an interstellar object during a recent revisit to comet 3I/ATLAS. The team’s results published recently in The […]

Juice-UVS saw gas and dust elements stretching up to more than 5 million km from 3I/ATLAS’s nucleus on November 25, 2025, when the comet had dimmed considerably relative to November 2 observations. Black spots are where stars appeared in the scanned image, removed here for clarity. Credit: NASA/ESA/Southwest Research Institute

Astrochemistry, Astrogeology, Comets and Asteroids, Europa, Icy Worlds, Imaging & Spectroscopy, Missions & Hardware, Press Release

Two Spacecraft Observed Both Hemispheres Of Interstellar Comet 3I/ATLAS Simultaneously

by Keith CowingMay 14, 2026May 14, 2026

The Southwest Research Institute-led Ultraviolet Spectrograph (UVS) instruments aboard ESA’s Jupiter Icy Moons Explorer (Juice) spacecraft and NASA’s Europa Clipper made unique observations of interstellar comet 3I/ATLAS in late 2025. […]

A new study of the interstellar comet 3I/ATLAS led by the University of Michigan shows that its water has a remarkably high content of deuterium. This form of hydrogen is comparatively less abundant in our solar system, enabling researchers to glean new insights about other planetary processes at work in our galaxy. Image credit: U-M News/Hans Anderson

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Press Release

The Interstellar Comet 3I/ATLAS Was Born Somewhere Much Different From Our Solar System

by Keith CowingApril 28, 2026April 28, 2026

Less than a year ago, astronomers discovered a comet soaring through our sky that was not from our solar system.

This artist’s impression compares the semi-heavy water content of the interstellar comet 3I/ATLAS (left) and Earth (right). Insets illustrate the relative abundance of deuterated water (HDO) molecules, showing that 3I/ATLAS contains over 30 times more HDO than is found in Earth’s oceans. This elevated ratio suggests the comet formed in an extremely cold environment, very different from the conditions that shaped our Solar System. Credit: NSF/AUI/NSF NRAO/M.Weiss

Astrochemistry, Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Press Release

ALMA Reveals Interstellar Comet 3I/ATLAS Formed in a Far Colder World Than Our Own

by Keith CowingApril 23, 2026April 23, 2026

New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) have yielded the first-ever measurement of deuterated water — also known as semi-heavy water — in an interstellar object. The discovery […]

SLC of comet 3I/ATLAS. The MPC observations show a much larger dispersion of the data than the COBS observations. There is a significant increase in brightness starting at -45 days before perihelion that we interpreted as the onset of water sublimation. The maximum reduced magnitude reached by the comet was mV(max)=6.8±0.15 mag. This plot and the next one may be considered as two of the highlights of the SLC Methodology. The other highlight is the Comet Evolutionary Diagram. -- astro-ph.EP

Astrochemistry, Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Imaging & Spectroscopy, Interstellar, Status Report

Secular Light Curve of Exocomet 3I/ATLAS, and its Location on a Comet Evolutionary Diagram

by Keith CowingApril 23, 2026April 23, 2026

In this work we will create the Secular Light Curve (SLC) of exocomet 3I/ATLAS, using the SLC-Methodology (Ferrin 2010-2023). The SLCs give a throve of new information and allow the […]

Top row: coma maps of H2O, CO2, and CH4, computed as the molecular column density from a pixel-by-pixel retrieval analysis for Observations 6, 15, and 6, respectively. The sunward and target velocity directions are denoted by the white arrows. The target centroids, computed as the photocenter in the median-stacked images (Figure 1), are marked with the black points. For H2O and CO2, the white contours correspond to emission levels of 50% and 20% relative to the maximum value and illustrate the slight anti-sunward extension of the respective comae. The contours are omitted in the CH4 panel due to the poorer signal-to-noise ratio of the data. Bottom row: corresponding median-stacked images across the continuum wavelengths within each fluorescence region. The H2O coma map shows significant enhancement in emission level at large nucleocentric distances relative to the dust continuum, indicating extended H2O production within the coma. -- arxiv.org

Astrochemistry, Astrogeology, Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Intelligence & Language, Interstellar, Press Release

Interstellar Comet Reveals Methane On Its Journey Through Our Solar System

by Keith CowingApril 18, 2026April 18, 2026

Interstellar comet 3I/ATLAS is now on its way out of our solar system, never to return.

Interstellar comet 3I/ATLAS (C/2025 N1) captured by the Subaru Telescope on December 13, 2025 (Hawaii-Aleutian Standard Time). This image was created by combining three different wavelengths: V-band (550 nanometers, depicted in blue), R-band (660 nanometers, depicted in green), and I-band (805 nanometers, depicted in red). (Credit: NAOJ)

Astrochemistry, Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Press Release

Subaru Telescope Captures Interstellar Comet 3I/ATLAS Composition Change

by Keith CowingApril 16, 2026April 16, 2026

The Subaru Telescope observed the interstellar comet 3I/ATLAS on January 7, 2026 (UT), after it made its closest approach to the Sun. By observing colors in the coma around the […]

The green-to-red intensity ratio of [O I] (G/R) in 3I (filled circle), compared with measurements for a sample of Solar System comets: Jupiter-family comets (JFCs; open triangles), Oort Cloud comets (OCCs; open squares), and Halley-type comets (HTCs; crosses) from A. Decock et al. (2013); A. McKay et al. (2015); Y. Shinnaka & H. Kawakita (2016); Y. Shinnaka et al. (2020), as well as C/2016 R2 from C. Opitom et al. (2019) and 2I/Borisov from C. Opitom et al. (2021). -- astro-ph.GA

A Post-perihelion Constraint On The CO2/H2O Ratio Of Interstellar Comet 3I/ATLAS From [O I] Forbidden Lines

by Keith CowingMarch 31, 2026March 31, 2026

We present high-resolution optical spectroscopy of interstellar comet 3I/ATLAS (C/2025 N1) obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope on UT 2026 January 7, when the comet […]

Upper Panels. Maps of N×ρ for CO, CO2, CH4, CH3OH, and H2O. The white arrow shows the projected direction of the Sun. Lower. Maps of molecular rotational temperatures. -- astro-ph.EP

Astrochemistry, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Status Report

Coma Physics Of An Interstellar Object: JWST Spatial-Spectral Mapping Of 3I/ATLAS

by Keith CowingMarch 30, 2026March 30, 2026

We report a survey of molecular emission from cometary volatiles using the James Webb Space Telescope (JWST) toward interstellar object 3I/ATLAS carried out on UT 2025 December 22 and 23 […]

D/H ratios in solar system and extrasolar sources. Ratios are for methane except when noted otherwise. Sources for which the D/H ratio in c−C3H2 was used to estimate the D/H in CH4 are denoted with a ⋆. References and values for each object are given in Extended Data Table 3. -- astro-ph.EP

Astrochemistry, Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Imaging & Spectroscopy, Status Report

Isotopic Signature of Organic Molecules from Beyond the Solar System: An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS

by Keith CowingMarch 27, 2026March 27, 2026

Interstellar objects are interlopers from other planetary systems, and their volatile compositions provide a glimpse into planet formation around their host star. We present near-infrared spectra of the coma of […]

3I/ATLAS

Webb Detects Methane on Interstellar Comet 3I/ATLAS

Two Spacecraft Observed Both Hemispheres Of Interstellar Comet 3I/ATLAS Simultaneously

The Interstellar Comet 3I/ATLAS Was Born Somewhere Much Different From Our Solar System

ALMA Reveals Interstellar Comet 3I/ATLAS Formed in a Far Colder World Than Our Own

Secular Light Curve of Exocomet 3I/ATLAS, and its Location on a Comet Evolutionary Diagram

Interstellar Comet Reveals Methane On Its Journey Through Our Solar System

Subaru Telescope Captures Interstellar Comet 3I/ATLAS Composition Change

A Post-perihelion Constraint On The CO2/H2O Ratio Of Interstellar Comet 3I/ATLAS From [O I] Forbidden Lines

Coma Physics Of An Interstellar Object: JWST Spatial-Spectral Mapping Of 3I/ATLAS

Isotopic Signature of Organic Molecules from Beyond the Solar System: An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS

Alta-X Drone Tests Future Astrobiology / Astrogeology Droid Technology

Landforms In Ares Vallis Carved Out By Ancient Water Flow

Evolution of Stellar Activity and Habitable Zone (EATEN): III. X-ray Activity of Dwarfs in Open Clusters and Field Stars

Radial Velocity Detection Of The TRAPPIST-1 Planetary System With SPIRou And NIRPS

Structure Of An RNA polymerase Ribozyme Replication Complex