Comet Archives

Spectral characterization of Chiron’s surface composition. a Comparison of the bestfit spectral model of the surface composition (red) with the measured spectrum (black). The surface is best described by an intimate mixture of water ice in both amorphous and crystalline phases, carbon dioxide ice, and tholin-like materials. b Residuals between the model and the data show an excellent fit, with a root mean square deviation that is just 1% higher than the average scatter in the data. c Zoomed-in view of the complex organic absorption feature spanning 3.3–3.6 µm, with the individual component bands indicated by dashed lines. Comparison between the measured spectrum and synthetic spectra of several candidate species, convolved to the spectral resolution of the data, points to C3H8 and/or ice tholins produced by the irradiation of H2O ice and C2H6 as the most plausible candidates for the observed organic feature. -- astro-ph.EP

Astrochemistry, Astrogeology, Biochemistry & Organic Chemistry, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Status Report

JWST Reveals Anomalously Enhanced Methane Outgassing From Below Chiron’s Water Ice And Carbon Dioxide Bearing Surface

by Keith CowingMay 26, 2026May 26, 2026

Centaurs are inward-scattered Kuiper belt objects, with some exhibiting comet-like activity. The physical mechanisms powering this activity remain poorly understood, with carbon monoxide (CO) sublimation or the crystallization of amorphous […]

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 […]

A summary of the CO and N2 reported in various comets with respect to parent molecule (top) and with respect to water (bottom).

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

CO and N2 Produced from H2O, CO2, and NH3 Cometary Ice Analogs

by Keith CowingApril 6, 2026April 6, 2026

Hypervolatile species such as carbon monoxide (CO) and molecular nitrogen (N2) have been detected in comets, and could be used to constrain comet formation temperature conditions if their presence is […]

Dust surface density evolution in the fiducial model without disk buildup (left) and with disk buildup taken into account (right). Time zero refers to the moment the gas disk reaches maximum mass in the model including its buildup, corresponding to the time the dust is initialized in the model without disk buildup. -- astro-ph.EP

Astrogeology, Astronomy & Telescopes, Exoplanets, -moons, -comets, Icy Worlds, Imaging & Spectroscopy, Status Report

Dust Evolution During Protoplanetary Disk Bbuildup Enhances CO Ice Relative To Water

by Keith CowingApril 1, 2026April 1, 2026

Water ice is expected to be the dominant volatile component of bodies formed in the outer Solar System. However, recent observations of comets and trans-Neptunian objects suggest that the relative […]

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 […]

Comet

JWST Reveals Anomalously Enhanced Methane Outgassing From Below Chiron’s Water Ice And Carbon Dioxide Bearing Surface

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

CO and N2 Produced from H2O, CO2, and NH3 Cometary Ice Analogs

Dust Evolution During Protoplanetary Disk Bbuildup Enhances CO Ice Relative To Water

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

Isobaric Crystallization of Aqueous Magnesium Chloride Solutions at Icy Moon Conditions

Systematic Uncertainties in Rocky Exoplanet Reflected Light from Incomplete Laboratory BRDF Measurements

New Discovery Links Hemispheres In The Mystery Of Earth’s Past Ice Ages

UV Photodamage Pathways And The Evolutionary Selection Of Thymine Over Uracil In Early Genetic Systems

Reversion To The Meta Body Form Of Life After Complete Cell Death In Pure Liquid Water