3I/ATLAS Archives

Multi-Wavelength Post-Perihelion Polarimetry of Interstellar Comet 3I/ATLAS

by Keith CowingSeptember 8, 2026September 8, 2026

[astro-ph.EP] We present new post-perihelion polarimetric observations of the third discovered interstellar object, 3I/ATLAS (C/2025 N1; hereafter 3I), obtained using FORS2 at the Very Large Telescope, ALFOSC at the Nordic […]

Example of the stacking procedure for the Maidanak data obtained on 2025 August 15, based on ten 60 s exposures in each of the B, V , and R filters. Left: Comet-centered stack, showing the coma morphology without trailing of the comet signal. The pink circle indicates an aperture radius of 10 000 km. Right: Sidereal stack used for photometric calibration, in which the comet appears trailed.-- [astro-ph.EP]

Comets and Asteroids

The Inbound Gas and Dust Evolution of Interstellar Comet 3I/ATLAS from Optical Spectroscopy and Multi-band Photometry

by Keith CowingAugust 24, 2026August 24, 2026

[astro-ph.EP] Interstellar objects (ISOs) provide direct constraints on the composition and evolution of extrasolar planetary systems. As the third confirmed ISO, comet 3I/ATLAS offers a rare opportunity to study pristine […]

3I/ATLAS CH4 + CH3D residual spectrum, generated by extracting a spectrum in a 1 ′′ .5 diameter aperture centered

Comets and Asteroids

An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS

by Keith CowingAugust 18, 2026August 19, 2026

[astro-ph.EP]. Interstellar objects are interlopers from other planetary systems, and their volatile compositions provide a glimpse into planet formation around their host star.

Candidate component r55 with period of P0 = 18.87 s in 1050–1140 MHz (a) and r952 with period of P0 = 16.58 s 1300–1450 MHz (b) in our search. The layout of the two panels are the same as Figure 1. -- [astro-ph.IM]

SETI & Technosignatures

Periodic Radio Technosignature Search Toward 3I/ATLAS With FAST

by Keith CowingJuly 13, 2026July 13, 2026

[astro-ph.IM] 3I/ATLAS, the third confirmed interstellar object discovered in the Solar System, provides a unique opportunity for targeted technosignature searches.

This image of interstellar comet 3I/ATLAS was taken on 18 January 2026 with the FORS2 instrument on ESO’s Very Large Telescope (VLT). It is a stack of several images spanning 14 minutes. As the comet moves on the sky, the stars appear as trails in the background. Credit: ESO/O. Hainaut

Comets and Asteroids

Older Than The Sun: Astronomers Find New Clues To The Origin Of Interstellar Comet 3I/ATLAS

by Keith CowingJuly 7, 2026July 7, 2026

[ESO] Astronomers have used the European Southern Observatory’s Very Large Telescope (ESO’s VLT) to study the composition of 3I/ATLAS, the brightest interstellar object ever seen, in detail.

Scatter plots of potential candidate in frequency, drift rate and signal-to-noise ratio for total intensity and four polarization channels. The color and the size for each point represent the value of SNR in log space. The blue and ornage color bar are the frequency ranges of civil aviation and navigation satellites, respectively. The black dashed lines represent the expected drift rates for each observation date. -- astro-ph.IM

SETI & Technosignatures

Narrowband Radio Technosignature Search Toward 3I/ATLAS with FAST

by Keith CowingJuly 3, 2026July 3, 2026

[astro-ph.IM] 3I/ATLAS is the third confirmed interstellar object passing through the Solar System.

Continuum-subtracted emissivity of 3I/ATLAS in the 6-7 µm region in black, compared to a set of reference spectra which are described in the main text.

Comets and Asteroids

The Dust Mineralogy of Interstellar Comet 3I/ATLAS from JWST/MIRI Observations

by Keith CowingJuly 3, 2026July 3, 2026

[astro-ph.EP] We present the first spectroscopic mineralogical analysis of the dust coma of an interstellar object (ISO) from JWST mid-infrared spectroscopy of 3I/ATLAS (3I).

Interstellar Comet 3I/ATLAS (NIRSpec IFU) -- ESA (larger Image)

Comets and Asteroids

Webb Finds Clues To The Ancient Origin Of Comet 3I/ATLAS

by Keith CowingJune 23, 2026June 23, 2026

The third identified interstellar comet in human history has a surprising chemical makeup, raising questions as to how common, or unusual, conditions in our own Solar System may be.

Panels (a)–(o) show contour maps of the observed isophotes (black lines) together with the corresponding modelled isophotes (red lines) for the case 𝑟max = 1 cm. For each of these contour panels, a companion plot is displayed to the right, labelled (a′ )–(o′ ), showing a one-dimensional scan extracted along the direction indicated by the straight red line in the corresponding contour map. In these primed panels, the black and red curves represent the observed and modeled brightness profiles, respectively. The 𝑥- and 𝑦-axes in the contour plots are given in pixel units, and the innermost isophote levels as well as the physical dimensions of each image are listed in Tables 1 and 3. In panels (a)–(o), isophote levels increase outward in steps of 1 mag. In the primed panels, the 𝑥-axis is expressed in pixel units and the 𝑦-axis in surface brightness units (mag arcsec−2). -- astro-ph.EP

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

Dust Colour, Phase Behaviour, And Monte Carlo Modelling Of Interstellar Comet 3I/ATLAS From 4 au Pre- to 4 au Post-Perihelion

by Keith CowingJune 19, 2026June 19, 2026

We report multi-band photometric imaging observations and Monte Carlo dust tail modelling of the interstellar comet 3I/ATLAS covering a wide range of heliocentric distances, from about 4 au pre-perihelion to […]