Résumé IA · arXiv: 2508.18382v2 · astro-ph.SR
Very Large Telescope Observations of Interstellar Comet 3I/ATLAS. II. From Quiescence to Glow: Dramatic Rise of Ni i Emission and Incipient CN Outgassing at Large Heliocentric Distances*
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Postperihelion Coma Composition of the Interstellar Comet 3I/ATLAS from Optical SpectroscopyRui-Ning Zhao, Xi-Liang Zhang, Bin Yang et al. · 2026 · Astrophysical Journal Letters · cité 2 fois · Pas encore résumé
Résumé scientifique
We present multiepoch optical spectroscopy of the interstellar comet 3I/ATLAS obtained between 2025 December and 2026 January (heliocentric distances of 1.8–3.3 au), yielding postperihelion production rates and mixing ratios for CN, C3, C2, CH, and gaseous metals (Fe i and Ni i). Our results show that the coma is less depleted in C2 after perihelion than before, indicative of subsurface activation or compositional heterogeneity. The outgassing profiles reveal a pronounced perihelion asymmetry: the CN and metal production rates decline more gradually outbound than inbound, consistent with the reported behavior of H2O and implying a change in the comet’s activity pattern across perihelion. Des…
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Preperihelion CN Production Rate of Interstellar Comet 3I/ATLASM. Lazzarin, A. Mura, F. La Forgia et al. · 2026 · Astrophysical Journal Letters · cité 4 fois · Pas encore résumé
Résumé scientifique
We present spectroscopic observations of the third interstellar comet 3I/ATLAS obtained with the DOLORES instrument on the 3.58 m Telescopio Nazionale Galileo on 2025 August 16 (rh = 2.98 au). The spectrum revealed a red slope of 12.68% ± 0.05%/1000 Å across the 5000–8000 Å range, consistent with previous findings. Observations show the CN outgassing violet band, which yields a production rate of (4.28 ± 0.83) · 1023 mol s−1. We derived upper limits for C2 and C3 production rates since no clear detection was possible and used those to compute C2/CN and C3/CN ratios. The resulting, notably low, values of −0.86 and −1.47, respectively, for C2/CN and C3/CN ratios classify 3I as a strongly carbo…
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Contemporaneous Optical and Near-infrared Observations of the Interstellar Comet 3I/ATLAS Pre- and PostperihelionK. Medler, W. Hoogendam, C. Ashall et al. · 2026 · Astronomical Journal · cité 3 fois · Pas encore résumé
Résumé scientifique
Interstellar objects provide a unique view into the formation of other star systems. Here we present spectroscopic observations of the recently discovered interstellar object 3I/ATLAS between a heliocentric distance of 3.7–1.8 au on either side of its travels through perihelion. We obtained several observations with the Keck-I/LRIS, Keck-II/NIRES, Gemini/GMOS, and UH88/SNIFS spectrographs, covering a wavelength range of 0.3–2.5 μm. We report the continued emission of both Ni and CN, along with postperihelion detections of Fe and a weak detection of C3. We determine the spectral slope across optical and near-infrared (NIR) wavelengths and find a positive spectral slope in the optical, with va…
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Onset of CN Emission in 3I/ATLAS: Evidence for Strong Carbon-chain DepletionLuis E. Salazar Manzano, Hsing-Wen Lin, Aster G. Taylor et al. · 2025 · Astrophysical Journal Letters · cité 19 fois · Pas encore résumé
Résumé scientifique
Interstellar objects provide a direct window into the environmental conditions around stars other than the Sun. The recent discovery of 3I/ATLAS, a new interstellar comet, offers a unique opportunity to investigate the physical and chemical properties of interstellar objects and to compare them with those of comets in our own solar system. In this Letter we present the results of a 10 night spectroscopic and photometric monitoring campaign with the 2.4 m Hiltner and 1.3 m McGraw–Hill telescopes at the MDM Observatory. The campaign was conducted between August 8 and 17 while 3I/ATLAS was inbound at heliocentric distances of 3.2–2.9 au. Our observations captured the onset of optical gas activi…
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Postperihelion Integral Field Spectroscopy of the Interstellar Comet 3I/ATLASW. Hoogendam, David O. Jones, Bin Yang et al. · 2026 · Astrophysical Journal · cité 4 fois · Pas encore résumé
Résumé scientifique
The environs of other stellar systems may be directly probed by analyzing the cometary activity of interstellar objects. The recently discovered interstellar object 3I/ATLAS was the subject of an intensive worldwide follow-up campaign in its preperihelion approach. Now, 3I/ATLAS has begun its postperihelion departure from the solar system. In this paper, we report the first postperihelion blue-sensitive integral-field unit spectroscopy of 3I/ATLAS using the Keck Cosmic Web Imager on 2025 November 16. We confirm previously reported CN, Fe, and Ni outgassing along with detections of carbon chain molecules C2 and C3. We calculate production rates for each species. We find Fe and Ni production r…
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Very Large Telescope observations of interstellar comet 3I/ATLASBaltasar Luco, T. Puzia, R. Rahatgaonkar et al. · 2026 · Astronomy & Astrophysics · Pas encore résumé
Résumé scientifique
Context . 3I/ATLAS is only the third known interstellar object to traverse the Solar System, and the first object for which both branches of the perihelion passage can be monitored at high spectral resolution. Aims . We characterize in 3I/ATLAS the heliocentric evolution of the CN production rate and the forbidden [O I ] emission, describe the broader emission line inventory, and release the analysis tools and reduced data products to the community. Methods . We obtained high-resolution ( R ≃ 140 000) spectroscopy of 3I/ATLAS on 23 nights with VLT/ESPRESSO ( r h = 1.67–2.45 au). The CN production rates were derived by fitting the B 2 Σ + − X 2 Σ + band using CometSpec, a publicly released Py…
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Pre-perihelion Emergence of the CN Gas Coma in 3I/ATLAS Temporally and Spatially Resolved by the 7-dimensional TelescopeG. Paek, Myungshin Im, M. Jeong et al. · 2026 · Astrophysical Journal · cité 3 fois · Pas encore résumé
Résumé scientifique
We present time series medium-band (R ∼ 20–40) observations of the third interstellar object (ISO) 3I/ATLAS (C/2025 N1) obtained with the 7-Dimensional Telescope, which enabled spatially resolved monitoring of its gas and dust activity from 2025 July to September. The m400-band image (λc = 400 nm, Δλ ≈ 25 nm) reveals an emergence of a pronounced and spatially extended CN emission at a heliocentric distance of rh < 3 au. This onset is consistently identified across multiple diagnostics, including a break in the light-curve evolution, excess reflectance, inward expansion of annular excess beyond 10,000–20,000 km, growth of the coma half-light radius from ∼11,000 to ∼19,000 km, and a rapid rise…
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Comprehensive Visible and Near-infrared Keck and Gemini Monitoring and Characterization of Interstellar Comet 3I/ATLAS during its Encounter with the Solar SystemB. Bolin, Jeff Cooke, B. Lemaux et al. · 2026 · Pas encore résumé
Résumé scientifique
We present 14 optical imaging and eight optical spectroscopic epochs of interstellar comet 3I/ATLAS from Keck/LRIS and Gemini/GMOS, two near-infrared (NIR) imaging epochs from Keck/MOSFIRE, and four NIR spectroscopic epochs from Gemini/Flamingos-2 and GNIRS, obtained between 2025 July and 2026 May. Mean GMOS colors of $g-r=0.732\pm0.029$, $r-i=0.237\pm0.025$, and $i-z=0.109\pm0.022$ mag show no significant change across perihelion. Phase-corrected red-band activity follows $Af\rho\propto r_h^{-2.10\pm0.14}$ inbound and $r_h^{-3.34\pm0.43}$ outbound. Transverse-width and sunward-plume speeds imply dust losses of $2.7\times10^9$ and $1.0\times10^{10}$ kg over 2025 July 3--2026 May 15 for 1-$\m…
Les travaux antérieurs sur lesquels il s’appuie
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JWST Detection of a Carbon-dioxide-dominated Gas Coma Surrounding Interstellar Object 3I/ATLASM. Cordiner, N. Roth, M. S. Kelley et al. · 2025 · Astrophysical Journal Letters · cité 59 fois · Pas encore résumé
Résumé scientifique
3I/ATLAS is the third confirmed interstellar object to visit our solar system and only the second to display a clear coma. Infrared spectroscopy with the James Webb Space Telescope (JWST) provides the opportunity to measure its coma composition and determine the primary activity drivers. We report the first results from our JWST NIRSpec campaign for 3I/ATLAS, at an inbound heliocentric distance of rH = 3.32 au. The spectral images (spanning 0.6–5.3 μm) reveal a CO2-dominated coma, with enhanced outgassing in the sunward direction and the presence of H2O, CO, water ice, dust, and a tentative detection of OCS. The coma CO2/H2O mixing ratio of 7.6 ± 0.3 is among the highest ever observed in a c…
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Interstellar comet 3I/ATLAS: discovery and physical descriptionB. Bolin, M. Belyakov, C. Fremling et al. · 2025 · cité 47 fois · Pas encore résumé
Résumé scientifique
We describe the physical characteristics of interstellar comet 3I/ATLAS, discovered on 2025 July 1 by the Asteroid Terrestrial-impact Last Alert System. The comet has eccentricity, $e$ $\simeq$ 6.08 and velocity at infinity, v$_{\infty}$ $\simeq$ 57 km/s, indicating an interstellar origin. \textbf{We obtained B,V, R, I, g, r, i, and z photometry with the Kottamia Astronomical Observatory 1.88-m telescope, the Palomar 200-inch telescope, and the Astrophysical Research Consortium 3.5-m telescope on 2025 July 2, 3, and 6. We measured colour indices B-V=0.98$\pm$0.23, V-R=0.71$\pm$0.09, R-I=0.14$\pm$0.10, g-r=0.84$\pm$0.05 mag, r-i=0.16$\pm$0.03 mag, i-z=-0.02$\pm$0.07 mag, and g-i=1.00$\pm$0.05…
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Detection of CN Gas in Interstellar Object 2I/BorisovA. Fitzsimmons, O. Hainaut, K. Meech et al. · 2019 · Astrophysical Journal · cité 90 fois · Pas encore résumé
Résumé scientifique
The detection of interstellar objects passing through the solar system offers the promise of constraining the physical and chemical processes involved in planetary formation in other extrasolar systems. While the effect of outgassing by 1I/2017 U1 (’Oumuamua) was dynamically observed, no direct detection of the ejected material was made. The discovery of the active interstellar comet 2I/Borisov means spectroscopic investigations of the sublimated ices is possible for this object. We report the first detection of gas emitted by an interstellar comet via the near-UV emission of CN from 2I/Borisov at a heliocentric distance of r = 2.7 au on 2019 September 20. The production rate was found to be…
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Snapshot of a new interstellar comet: 3I/ATLAS has a red and featureless spectrum.C. Opitom, C. Snodgrass, E. Jehin et al. · 2025 · Monthly Notices of the Royal Astronomical Society Letters · cité 34 fois · Pas encore résumé
Résumé scientifique
The interstellar comet 3I/ATLAS is only the third interstellar object to be discovered. Pre-perihelion measurements provide a unique opportunity to study its activity and composition, which may alter as it is heated in the coming months. We provide an initial baseline from optical spectroscopic observations obtained only two days after discovery, using the MUSE instrument on the VLT on 2025 July 3, while 3I was at 4.47 au from the Sun and 3.46 au from the Earth. These observations confirm the cometary nature of 3I, and reveal a red coma with a spectral slope of (18 ± 4)%_1000 Å in the 5000-9000 Å range, redder than most Solar System comets but similar to the surface colour of some Solar Syst…
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Iron and nickel atoms in cometary atmospheres even far from the SunJ. Manfroid, D. Hutsemékers, E. Jehin · 2021 · Nature · cité 33 fois · Pas encore résumé
Résumé scientifique
In comets, iron and nickel are found in refractory dust particles or in metallic and sulfide grains1. So far, no iron- or nickel-bearing molecules have been observed in the gaseous coma of comets2. Iron and a few other heavy atoms, such as copper and cobalt, have been observed only in two exceptional objects: the Great Comet of 18823 and, almost a century later, C/1965 S1 (Ikeya–Seki)4–9. These sungrazing comets approached the Sun so closely that refractory materials sublimated, and their relative abundance of nickel to iron was similar to that of the Sun and meteorites7. More recently, the presence of iron vapour was inferred from the properties of a faint tail in comet C/2006 P1 (McNaught)…
Les articles qui le citent
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The Volatile Inventory of 3I/ATLAS as Seen with JWST/MIRIM. Belyakov, Ian Wong, B. Bolin et al. · 2026 · Astrophysical Journal Letters · cité 15 fois · Pas encore résumé
Résumé scientifique
We present the first spectroscopic characterization of an interstellar object at mid-infrared wavelengths. Postperihelion observations of 3I/ATLAS (3I) using the JWST/MIRI medium-resolution spectrometer were obtained on 2025 December 15–16 and 27, when the object was at heliocentric distances of 2.20 and 2.54 au, respectively. Our 5–28 μm spectra exhibit fluorescence features from several gaseous species, including the ν2 band of H2O at 5.8–7.0 μm, the primary ν2 and associated hot bands of CO2 around 15 μm, and a forbidden transition of atomic nickel at 7.507 μm. We also report the first direct detection of CH4 in an interstellar object. The sharp rise in CH4 production relative to H2O sugg…
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IFU Observations of Comet 3I/ATLAS = C/2025 N1 (ATLAS) Using the Hobby–Eberly Telescope with the VIRUS InstrumentA. Cochran, Gregory Zeimann, E. Jehin et al. · 2026 · The Planetary Science Journal · Pas encore résumé
Résumé scientifique
We observed interstellar object 3I/ATLAS = C/2025 N1 (ATLAS) on 2025 December 9 UT with the VIRUS spectrograph on the Hobby–Eberly Telescope. VIRUS is a low spectral resolving power, multi-integral field unit (IFU), optical spectrograph. We used a single IFU for the observations and were able to obtain spectra spaced every 1″ (1327 km) from the optocenter out to about 85,000 km in the sunward direction. The spectra include molecular features normally seen in the optical for spectra of solar system comets, with the addition of many very strong lines of Fe I and Ni I. We modeled these observations using the Haser (1957) model framework and find that the data can only be fit if we assume that t…
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Rapid Brightening of 3I/ATLAS Ahead of PerihelionQicheng Zhang, K. Battams · 2025 · Publications of the Astronomical Society of the Pacific · cité 9 fois · Pas encore résumé
Résumé scientifique
Interstellar comet 3I/ATLAS has been approaching its 2025 October 29 perihelion while opposite the Sun from Earth, hindering ground-based optical observations over the preceding month. However, this geometry placed the comet within the fields of view of several space-based solar coronagraphs and heliospheric imagers, enabling its continued observation during its final approach toward perihelion. We report photometry from STEREO-A’s SECCHI HI1 and COR2, SOHO’s LASCO C3, and GOES-19’s CCOR-1 instruments in 2025 September–October, which show a rapid rise in the comet’s brightness scaling with heliocentric distance r as r−7.5±1.0. CCOR-1 also resolves the comet as an extended source with an appa…
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Comet 3I/Atlas: Divergent Insight and ExplanationJ. Herndon · 2026 · European Journal of Applied Sciences · Pas encore résumé
Résumé scientifique
The “various anomalous characteristics determined from photometric and astrometric observations” that inspired thoughts that comet 3I/Atlas might represent alien other-world technology, when viewed from a perspicacious perspective, are not necessarily un-natural at all. The “anomalous characteristic” of nickel observed with little or no iron evokes a divergent insight and explanation that 3I/Atlas contains a mass of nickel silicide analogous to Earth’s nickel silicide inner core. The “anomalous characteristic” of 3I/Atlas’ collimated jet pointing directly at the sun begs the question of both energy source and collimating mechanism. The divergent insight and explanation for 3I/Atlas’ internal…
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HATPI Preperihelion Time-series Photometry of the Interstellar Comet 3I/ATLASJ. Hartman, G. Bakos, Andrés Jordán et al. · 2026 · Astronomical Journal · cité 3 fois · Pas encore résumé
Résumé scientifique
The Hungarian-made Automated Telescope PI Steradians (HATPI) is a recently commissioned time-domain facility at Las Campanas Observatory, Chile, that uses 64 wide-angle, 9.6 cm diameter lenses and back-illuminated CCDs, yielding a mosaic field-of-view of 7100 square arcdegrees, observing the night sky at a cadence of 45 s and a spatial scale of 19 .″ 7 pixel−1. In this paper, we present moving object time-series photometry with this facility, focusing on the interstellar comet 3I/ATLAS, which was first robustly recovered by HATPI on the night of 2025 July 2 (one night after its discovery) at a Gaia G-band magnitude of G = 17.796 ± 0.082 mag (±0.030 mag systematic uncertainty). The comet then…
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