3I/ATLAS Archives

Interstellar Comet 3I/ATLAS As Seen By NASA's MAVEN Mission Larger imagery

Astrochemistry, Astrogeology, Astronomy & Telescopes, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Press Release

Interstellar Comet 3I/ATLAS As Seen By MAVEN

by Keith CowingNovember 19, 2025November 19, 2025

An ultraviolet image composite of the hydrogen atoms surrounding comet 3I/ATLAS, the third interstellar object ever detected by astronomers, as it passes through our solar system.

The temperature versus depth and time for 𝜅 = 10−4 W m−1 K−1 , 10−3 W m−1 K−1, and 10−2 W m−1 K−1 (top, middle, and bottom panels). The sublimation temperatures of CO (30 K, dash), CO2 (80 K, dash-dot), and H2O (150 K, dot) are shown as white contours. The depth of heat penetration and volatile activation strongly depends on the thermal conductivity 𝜅. Note that the range of the 𝑦-axis is different for each panel. -- astro-ph.EP

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

Potential Thermal Profiles of The Third Interstellar Object 3I/ATLAS

by Keith CowingNovember 3, 2025November 3, 2025

We investigate the thermal evolution of 3I/ATLAS, the third macroscopic interstellar object discovered on 2025 July 1.

Schematic illustration of interstellar comet 3I/ATLAS showing the expected stratigraphy of an irradiated nucleus. Galactic cosmic ray irradiation over several Gyr alters the outer ∼15–20 m, producing a CO2-rich crust through CO-to-CO2 conversion, ongoing CO release from the breakdown of irradiated organics, an organic-rich refractory mantle with a red spectral slope, and compact amorphous ice characterized by low diffusivity and high thermal conductivity. Beneath this layer lies a pristine, unprocessed interior shielded from GCRs, whose composition and structure remain unknown but are expected to differ markedly from the irradiated crust. -- astro-ph.EP

Astronomy & Telescopes, Biochemistry & Organic Chemistry, Biosignatures & Paleobiology, Comets and Asteroids, Icy Worlds, Interstellar, Status Report

Interstellar Comet 3I/ATLAS: Evidence for Galactic Cosmic Ray Processing

by Keith CowingNovember 3, 2025November 3, 2025

Spectral observations of 3I/ATLAS (C/2025 N1) with JWST/NIRSpec and SPHEREx reveal an extreme CO2 enrichment (CO2/H2O = 7.6+-0.3) that is 4.5 sigma above solar system comet trends and among the […]

Sample images showing the morphological development of 3I/ATLAS. The image dates and heliocentric distances of the comet are shown in each panel, as is a 10′′ scale bar. Sunward is West. The location of the brightest pixel is marked with a red dot, showing that the dust is extended asymmetrically towards the West in the early data, reversing to the East as the radiation pressure swept tail develops in the later data. -- astro-ph.EP

Astronomy & Telescopes, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Status Report

Pre-perihelion Development of Interstellar Comet 3I/ATLAS

by Keith CowingOctober 22, 2025October 22, 2025

We describe pre-perihelion optical observations of interstellar comet 3I/ATLAS taken during July – September 2025 using the Nordic Optical Telescope.

Simulation of 3I/ATLAS’s ion tail on 1 November 2025 assuming a 460 kms−1 radial flow. Positions of Europa Clipper, Sun, Hera, and 3I/ATLAS are shown in a frame where the Sun-Europa Clipper line is fixed. The plane represents that of the ecliptic, with grid lines spaced at 0.1 au. The comet’s position is shown every 6 hours, with legs showing its position north of the ecliptic. Europa Clipper is also north of the ecliptic by 0.069 au. Earth and Mars’s mean orbital distances are included for scale. -- astro-ph.EP

Astrochemistry, Astrogeology, Astronomy & Telescopes, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Status Report

Prospects For The Crossing Of Comet 3I/ATLAS’s Ion Tail

by Keith CowingOctober 21, 2025October 21, 2025

During October – November 2025, interstellar comet 3I/ATLAS, will pass upstream of the Europa Clipper and Hera spacecraft.

The Transiting Exoplanet Survey Satellite observed the interstellar comet 3I/ATLAS in 2025 May–June.

Astronomy & Telescopes, Biochemistry & Organic Chemistry, Comets and Asteroids, Icy Worlds, Imaging & Spectroscopy, Interstellar, Status Report

A Search For Coma In TESS Observations Of Interstellar Comet 3I/ATLAS

by Keith CowingOctober 14, 2025October 14, 2025

Using this extensive data set, we coadded more than 9000 images, in two groups, to look for extended coma that would unambiguously reveal cometary activity. The radial profiles in both […]

Degree of linear polarization as a function of phase angle measured in the R filter for 7 distant comets and for the interstellar Comet 3I/ATLAS (Z. Gray et al. 2025).

Astrogeology, Astronomy & Telescopes, Comets and Asteroids, Imaging & Spectroscopy, Interstellar, Status Report

Comparative Analysis of Polarization in Interstellar Comet 3I/ATLAS with Distant Solar System Comets

by Keith CowingOctober 9, 2025October 9, 2025

We analyze polarimetric measurements of the interstellar Comet 3I/ATLAS reported recently by Z. Gray et al. Comparison with distant solar system comets suggests no significant difference in the microphysics of […]

NASA’s Swift Ultraviolet/Optical Telescope (UVOT) observed interstellar comet 3I/ATLAS during two visits in July and August 2025.

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

Astrochemistry: Physicists Uncork A Message In A Bottle From Another Star

by Keith CowingOctober 8, 2025October 8, 2025

For millions of years, a fragment of ice and dust drifted between the stars—like a sealed bottle cast into the cosmic ocean. This summer, that bottle finally washed ashore in […]

ExoMars TGO image of comet 3I/ATLAS -- ESA

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

ExoMars And Mars Express Observe Interstellar Comet 3I/ATLAS

by Keith CowingOctober 7, 2025October 7, 2025

Between 1 and 7 October, ESA’s ExoMars Trace Gas Orbiter (TGO) and Mars Express spacecraft turned their eyes towards interstellar comet 3I/ATLAS, as it passed close to Mars.