Discovery and designation

A comet was discovered by the Asteroid Terrestrial-impact Last Alert System (ATLAS) in Chile and reported on 1 July 2025, temporarily designated A11pl3Z. Within 6 hours of the ATLAS detection, additional observations were identified from 28-29 June 2025 by the Zwicky Transient Facility (ZTF), sufficient to show that the orbit was extremely hyperbolic (Seligman et al., 2025). Follow up observations were conducted during the first 24 hours from many facilities, plus additional pre-discovery observations were found with the earliest being from ZTF on 14 June 2025. On 2 July the Minor Planet Center assigned it the designation 3I/ATLAS as the third interstellar object (after 1I/'Oumuamua and 2I/Borisov) plus the cometary designation C/2025 N1 (ATLAS). Pre-discovery observations were later identified from as early as 15 May 2025. At the time of discovery 3I/ATLAS was 4.5 AU from the Sun, 3.5 AU from the Earth, and had a magnitude of ~17.8.

Orbit and ephemeris (MPC, 2025)

perihelion distance q: eccentricity e: inclination i: ascending node Ω: longitude of perihelion ω: time of perihelion Tp: Epoch: absolute magnitude H: data arc:

1.3745928 AU 6.2769203 175.11669° 322.27219° 127.79317° 2025 Oct 29.21095 2025 May 5.0 - 19 days (2025 Jun 14-Jul 2), 122 obs.

Orbit and ephemeris (JPL, 2026)

perihelion distance q: eccentricity e: inclination i: ascending node Ω: longitude of perihelion ω: mean anomaly M: time of perihelion Tp: Epoch: nongravitational parameter A1: nongravitational parameter A2: nongravitational parameter A3: total magnitude M1: total magnitude slope K1: data arc:

1.3564811 ± 0.0000038 AU 6.141351 ± 0.000025 175.116457 ± 0.000019° 322.169609 ± 0.000071° 128.02287 ± 0.00010° 818.2202 ± 0.0029° 2025 Oct 29.495263 ± 0.000051 2026 Feb 19.0 (53.2 ± 1.2) x 10-9 AU/day2 (11.5 ± 2.1) x 10-9 AU/day2 (-6.85 ± 0.18) x 10-9 AU/day2 12.5 ± 0.9 4.5 280 days (2025 May 15-2026 Feb 19), 782 obs.

date	magnitude	distance to Sun (AU)	distance to Earth (AU)	notes
2013 Jan 01	33.20	157.990	158.950
2014 Jan 01	32.87	145.748	146.706
2015 Jan 01	32.51	133.505	134.463
2016 Jan 01	32.11	121.261	122.218
2017 Jan 01	31.67	108.982	109.942
2018 Jan 01	31.18	96.733	97.693
2019 Jan 01	30.63	84.480	85.440
2020 Jan 01	29.99	72.222	73.181
2021 Jan 01	29.22	59.921	60.884
2022 Jan 01	28.29	47.644	48.607
2023 Jan 01	27.07	35.350	36.315
2024 Jan 01	25.33	23.033	24.001
2024 Jul 01	23.83	16.876	15.874
2025 Jan 01	22.25	10.638	11.618
2025 Jan 15	22.06	10.163	11.132
2025 Feb 01	21.82	9.586	10.466
2025 Feb 15	21.59	9.111	9.860
2025 Mar 01	21.34	8.636	9.210
2025 Mar 15	21.06	8.161	8.523
2025 Apr 01	20.68	7.584	7.658
2025 Apr 15	20.34	7.109	6.935
2025 May 01	19.91	6.568	6.116
2025 May 15	19.50	6.094	5.423	earliest pre-discovery observation
2025 Jun 01	18.97	5.520	4.640
2025 Jun 11	18.64	5.184	4.220	crosses Jupiter's orbit inbound
2025 Jun 14	18.54	5.083	4.102	earliest pre-discovery observation used for announcement
2025 Jun 15	18.51	5.050	4.063
2025 Jul 01	17.97	4.514	3.507	discovery
2025 Jul 15	17.51	4.049	3.127
2025 Aug 01	16.99	3.492	2.811
2025 Aug 15	16.60	3.042	2.661
2025 Sep 01	16.16	2.515	2.575
2025 Sep 15	15.79	2.110	2.542
2025 Oct 01	15.34	1.709	2.500
2025 Oct 03	15.28	1.665	2.492	closest approach to Mars (0.194 AU)
2025 Oct 15	14.96	1.456	2.429
2025 Oct 29	14.72	1.356	2.311	perihelion
2025 Nov 01	14.69	1.359	2.280
2025 Nov 03	14.68	1.366	2.257	closest approach to Venus (0.649 AU)
2025 Nov 07	14.67	1.391	2.211	brightest as seen from Earth
2025 Nov 15	14.69	1.484	2.110
2025 Dec 01	14.86	1.800	1.911
2025 Dec 15	15.09	2.166	1.804
2025 Dec 19	15.18	2.280	1.797	closest approach to Earth
2026 Jan 01	15.58	2.667	1.873
2026 Jan 15	16.17	3.106	2.144
2026 Feb 01	16.99	3.655	2.699
2026 Feb 15	17.65	4.115	3.287
2026 Mar 01	18.26	4.581	3.949
2026 Mar 15	18.80	5.049	4.654
2026 Mar 17	18.88	5.117	4.756	closest approach to Jupiter (0.360 AU)
2026 Mar 20	18.98	5.217	4.911	crosses Jupiter's orbit outbound
2026 Apr 01	19.39	5.621	5.535
2026 Apr 15	19.82	6.094	6.260
2026 May 01	20.25	6.635	7.070
2026 May 15	20.58	7.109	7.748
2026 Jun 01	20.94	7.685	8.521
2026 Jun 15	21.20	8.160	9.106
2026 Jul 01	21.47	8.703	9.712
2026 Jul 15	21.67	9.178	10.185
2026 Aug 01	21.90	9.755	10.687
2026 Aug 15	22.06	10.230	11.044
2026 Sep 01	22.24	10.807	11.416
2026 Oct 01	22.52	11.824	11.955
2026 Nov 01	22.77	12.876	12.469
2026 Dec 01	23.03	13.893	13.078
2027 Jan 01	23.31	14.943	13.961
2028 Jan 01	25.86	27.280	26.299
2029 Jan 01	27.43	39.614	38.634
2030 Jan 01	28.55	51.895	50.916
2035 Jan 01	31.79	113.223	112.244
2040 Jan 01	33.58	174.462	173.483
2045 Jan 01	34.83	235.697	234.719
2050 Jan 01	35.78	296.896	295.918

Confirmation as interstellar in origin

3I/ATLAS is the most hyperbolic object yet observed with an eccentricity of 6.14; its velocity relative to the Sun prior to significant influence of the Sun's gravity was 57.9 km/s. The hyperbolic nature was confirmed within hours of discovery (Seligman et al., 2025).

Follow-up observations

3I/ATLAS will come no closer than 1.8 AU to the Earth, making telescopic observations challenging. However, its path is close to the ecliptic and it passed only 0.19 AU from Mars on 3 October 2025 and will pass only 0.36 AU from Jupiter on 16 March 2026. Consequently several planetary probes have been and will be tasked to make observations (though obviously with much smaller telescopes than ground-based ones).

Cometary activity

Faint activity was visible in images from the Canada-France-Hawaii Telescope (CFHT) on 2 July with an elongated coma visible in images from the European Southern Observatory Very Large Telescope (ESO VLT) on 4 July (Seligman et al., 2025).

Size

The nucleus of 3I/ATLAS itself is unresolved. Hubble Space Telescope observations suggest its diameter is between 0.44 and 5.6 km (Jewitt et al., 2025). The lower limit is set by assumptions about the volatile which is driving coma formation and the upper limit by an assumed cometary albedo and coma brightness distribution; the actual size is more likely towards the lower limit. Estimates based on observed non-gravitational acceleration suggest a diameter between 0.82 and 1.05 km (Forbes and Butler, 2025), using assumptions regarding outgassing asymmetry and density (0.5 g/cm³ assumed).

De la Fuente Marcos et al. (2025) report a rotation period of 16.79 ± 0.23 h and an amplitude of ~0.2 magnitude, which suggests a relatively small elongation of >1.2 for the nucleus (though this depends on how much of 3I's brightness is from the dust coma rather than the nucleus).

References

--articles and preprints on 3I/ATLAS (from newest to oldest; arXiv posting date in parentheses)

• Hutsemekers, D., et al., (8 May 2026), Origin and evolution of NiI and FeI in the coma of the interstellar comet 3I/ATLAS throughout its trajectory, arXiv, on line, 2605.07652.
• Horns, D., N. Knop, and M. Mohammadidoust, (6 May 2026), Contribution of interstellar objects to local dark matter density, arXiv, on line, 2605.04801.
• Scarmato, T., and A. Loeb, (20 April 2026), Linking System of Jets to the Non-Gravitational Acceleration of 3I/ATLAS, arXiv, on line, 2604.18773.
• Ferrin, I., et al., (19 April 2026), Secular Light Curve of Exocomet 3I/ATLAS, and its Location on a Comet Evolutionary Diagram, arXiv, on line, 2604.09941.
• Shinnaka, Y., et al., (26 March 2026), A post-perihelion constraint on the CO2/H2O ratio of interstellar comet 3I/ATLAS from [O I] forbidden lines, arXiv, on line, 2603.25002.
• Biver, N., et al., (24 March 2026), Perihelion observations of interstellar comet 3I/ATLAS with the IRAM 30-m telescope, arXiv, on line, 2603.23240.
• Roth, N. X., et al., (20 March 2026), Coma Physics of an Interstellar Object: JWST Spatial-Spectral Mapping of 3I/ATLAS, arXiv, on line, 2603.20460.
• Roth, N. X., et al., (20 March 2026), Isotopic Signature of Organic Molecules from Beyond the Solar System: An Enriched Methane D/H Ratio in the Interstellar Object 3I/ATLAS, arXiv, on line, 2603.20445.
• Li, J.-K., Z.-Z. Tao, and T.-J. Zhang, (19 March 2026), Narrowband Radio Technosignature Search toward 3I/ATLAS with FAST, arXiv, on line, 2603.19023.
• Thoss, V., A. Loeb, and A. Burkert, (16 March 2026), Inferring the mass and size of 3I/ATLAS from its non-gravitational acceleration, arXiv, on line, 2603.15735.
• Ren, X., et al., (10 March 2026), Interstellar Object 3I/ATLAS Observed from Mars by China's Tianwen-1 Spacecraft, arXiv, on line, 2603.10350.
• Zhao, R., et al., (8 March 2026), Post-perihelion Coma Composition of the Interstellar Comet 3I/ATLAS from Optical Spectroscopy, arXiv, on line, 2603.07718.
• Opitom, C., et al., (7 March 2026), High nitrogen and carbon isotopic ratios in the interstellar comet 3I/ATLAS, arXiv, on line, 2603.07187.
• Salazar Manzano, L. E., et al., (6 March 2026), Water D/H in 3I/ATLAS as a Probe of Formation Conditions in Another Planetary System, arXiv, on line, 2603.07026.
• Cordiner, M., et al., (6 March 2026), Isotopic Evidence for a Cold and Distant Origin of the Interstellar Object 3I/ATLAS, arXiv, on line, 2603.06911.
• Gillan, A. F., et al., (1 March 2026), Time-Domain Photometry and Activity Evolution of Interstellar Comet 3I/ATLAS with BHTOM, arXiv, on line, 2603.01383.
• Spada, F., M. Krolikowska, and L. Dones, (28 Feb. 2026), Systematic and Statistical Uncertainties in the Non-Gravitational Acceleration of 3I/ATLAS, arXiv, on line, 2603.00782.
• Medler, K., et al., (26 Feb. 2026), Contemporaneous Optical and Near-Infrared Observations of the Interstellar Comet 3I/ATLAS Pre- and Post-Perihelion, arXiv, on line, 2602.23586.
• Hartman, J. D., et al., (25 Feb. 2026), HATPI Pre-Perihelion Time-series Photometry of the Interstellar Comet 3I/ATLAS, arXiv, on line, 2502.21586.
• Scarmato, T., and A. Loeb, (19 Feb. 2026), Periodic Wobble of the Post-Perihelion Jet Structure Around 3I/ATLAS, arXiv, on line, 2502.18512.
• Li, J., et al., (15 Feb. 2026), Pre-perihelion Volatile Evolution of Interstellar Comet 3I/ATLAS Indicating Significant Contribution from Extended Source in the Coma, arXiv, on line, 2502.14218.
• Paek, G. S. H., et al., (13 Feb. 2026), Pre-perihelion Emergence of the CN Gas Coma in 3I/ATLAS Temporally and Spatially Resolved by the 7-Dimensional Telescope, arXiv, on line, 2502.12930.
• Martinez-Palomera, J., A. Tuson, and the TESS Science Support Center, (12 Feb. 2026), TSSC comet-centered data products from TESS 3I/ATLAS observations, arXiv, on line, 2502.12364.
• Monk, H., and D. Z. Seligman, (4 Feb. 2026), A Two-Dimensional Analytic Solution for the Generation of Hyperbolic Trajectories Via A Single Close Encounter with Applications To Interstellar Objects, arXiv, on line, 2502.04806.
• Belyakov, M., et al., (29 Jan. 2026), The Volatile Inventory of 3I/ATLAS as seen with JWST/MIRI, arXiv, on line, 2501.22034.
• Hui, M.-T., et al., (29 Jan. 2026), Nucleus and Postperihelion Activity of Interstellar Object 3I/ATLAS Observed by Hubble Space Telescope, arXiv, on line, 2501.21569.
• Ahuja, G., and S. Ganesh, (23 Jan. 2026), Effect of different Non-Gravitational accelerations on the trajectory of Interstellar Comet 3I/ATLAS, arXiv, on line, 2501.17083.
• Hoogendam, W. B., et al., (23 Jan. 2026), Post-Perihelion Integral Field Spectroscopy of the Interstellar Comet 3I/ATLAS, arXiv, on line, 2501.16983.
• Tan, H., X. Yan, and J.-Y. Li, (21 Jan. 2026), Perihelion Asymmetry in the Water Production Rate of the Interstellar Object 3I/ATLAS, arXiv, on line, 2501.15443.
• Scarmato, T., and A. Loeb, (15 Jan. 2026), Rotation Period of 3I/ATLAS After Perihelion from Jet Position Angle Wobble and Photometric Variability, arXiv, on line, 2501.10860.
• Barbieri, M., and A. Loeb, (13 Jan. 2026), Rare Near-Opposition Alignment of 3I/ATLAS on 22 January, 2026, arXiv, on line, 2501.08624.
• Choi, S., et al., (13 Jan. 2026), Dust Properties of the Interstellar Object 3I/ATLAS Revealed by Optical and Near-Infrared Polarimetry, arXiv, on line, 2501.08591.
• Lisse, C. M., et al., (10 Jan. 2026), SPHEREx Re-Observation of Interstellar Object 3I/ATLAS in December 2025: Detection of Increased Post-Perihelion Activity, Refractory Coma Dust, and New Coma Gas Species, arXiv, on line, 2501.06759.
• Hibberd, A., and T. M. Eubanks, (5 Jan. 2026), Catching 3I/ATLAS Using a Solar Oberth, arXiv, on line, 2501.02533.
• Scarmato, T., (26 Dec. 2025), Interstellar Interloper 3I/ATLAS: Nucleus Size, Photometry in RGB, Af(rho) and Antitail Structure Analysis, arXiv, on line, 2512.22365.
• Combi, M. R., et al., (26 Dec. 2025), Water Production of Interstellar Comet 3I/ATLAS from SOHO/SWAN Observations after Perihelion, arXiv, on line, 2512.22354.
• Jacobson-Bell, B., et al., (20 Dec. 2025), Breakthrough Listen Observations of 3I/ATLAS with the Green Bank Telescope at 1-12 GHz, arXiv, on line, 2512.19763.
• Forbes, J. C., and H. Butler, (20 Dec. 2025), The size of 3I/ATLAS from non-gravitational acceleration, arXiv, on line, 2512.18341.
• Sheikh, S. Z., et al., (19 Dec. 2025), A Search for Radio Technosignatures from Interstellar Object 3I/ATLAS with the Allen Telescope Array, arXiv, on line, 2512.18142.
• Serra-Ricart, M., J. Licandro, and M. R. Alarcon, (14 Dec. 2025), Pre-perihelion detection of a wobbling high-latitude jet in the interstellar comet 3I/ATLAS, arXiv, on line, 2512.12819.
• Hoogendam, W. B., et al., (9 Dec. 2025), University of Hawaii 88-inch Telescope Observations of the Interstellar Comet 3I/ATLAS: Spectrophotometric Blue-Sensitive Spectral Time Series Spanning Two Months from Discovery, arXiv, on line, 2512.09020.
• Lisse, C. M., et al., (8 Dec. 2025), SPHEREx pre-perihelion mapping of H2O, CO2, and CO in interstellar object 3I/ATLAS, arXiv, on line, 2512.07318.
• Hinkle, J. T., et al., (1 Dec. 2025), JCMT Constraints on the Early-Time HCN and CO Emission and HCN Temporal Evolution of 3I/ATLAS, arXiv, on line, 2512.02106.
• Roth, N. X., et al., (25 Nov. 2025), CH3OH and HCN in Interstellar Comet 3I/ATLAS Mapped with the ALMA Atacama Compact Array: Distinct Outgassing Behaviors and a Remarkably High CH3OH/HCN Production Rate Ratio, arXiv, on line, 2511.20845.
• Eubanks, T. M., et al., (25 Nov. 2025), Tracking the Activity of the Interstellar Object 3I/ATLAS through its Perihelion, arXiv, on line, 2511.20810.
• Scarmato, T., (21 Nov. 2025), Measuring Cometary Nuclei Behind Bright Comae: PSF Delta Decomposition with Bicubic Resampling and an Application to Interstellar Comet 3I/ATLAS C/2025 N1, arXiv, on line, 2511.19467.
• Trigo-Rodriguez, J. M., M. Gritsevich, and J. Blum, (25 Nov. 2025), Spectrophotometric evidence for a metal-bearing, carbonaceous, and pristine interstellar comet 3I/ATLAS, arXiv, on line, 2511.19112.
• Ahuja, G., and S. Ganesh, (20 Nov. 2025), Dynamical simulation of the Interstellar Comet 3I/ATLAS, arXiv, on line, 2511.16247.
• Maggiolo, R., F. Dhooghe, G. Gronoff, J. de Keyser, and G. Cessateur, (30 Oct. 2025), Interstellar Comet 3I/ATLAS: Evidence for Galactic Cosmic Ray Processing, arXiv, on line, 2510.26308.
• Yaginuma, Atsuhiro, Aster G. Taylor, and Darryl Z. Seligman, (28 Oct. 2025), Potential Thermal Profiles of The Third Interstellar Object 3I/ATLAS, arXiv, on line, 2510.25945.
• Zhang, Qicheng, and Karl Battams, (28 Oct. 2025), Rapid Brightening of 3I/ATLAS Ahead of Perihelion, arXiv, on line, 2510.25035.
• Jewitt, David, and Jane Luu, (21 Oct. 2025), Pre-perihelion Development of Interstellar Comet 3I/ATLAS, arXiv, on line, 2510.18769.
• Keto, Eric, and Abraham Loeb, (20 Oct. 2025), A Physical Model for the Ice Coma of 3I/ATLAS, arXiv, on line, 2510.18157.
• Grant, Samuel R., and Geraint H. Jones, 14 Oct. 2025 (15 Oct. 2025), Prospects for the Crossing of Comet 3I/ATLAS's Ion Tail, RNAAS, 9:276; arXiv, on line, 2510.13222.
• Hoogendam, W. B., et al., (13 Oct. 2025), Spatial Profiles of 3I/ATLAS CN and Ni Outgassing from Keck/KCWI Integral Field Spectroscopy, arXiv, on line, 2510.11779.
• Farnham, Tony L., Maximus Hood, Michael S. P. Kelley, and Jessica M. Sunshine, 7 Oct. 2025, A Search for Coma in TESS Observations of Interstellar Comet 3I/ATLAS, RNAAS, 9:266, on line at RNAAS.
• Zubko, Evgenij, and Gorden Videen, Oct. 2025, Comparative Analysis of Polarization in Interstellar Comet 3I/ATLAS with Distant Solar System Comets, RNAAS, 9:257, on line at RNAAS.
• Coulson, Iain M., et al., (3 Oct. 2025), JCMT detection of HCN emission from 3I/ATLAS at 2.1 AU, arXiv, on line, 2510.02817.
• Hutsemekers, Damien, et al., (30 Sept. 2025), Extreme NiI/FeI abundance ratio in the coma of the interstellar comet 3I/ATLAS, arXiv, on line, 2509.26503.
• Cloete, Richard, Abraham Loeb, Peter Veres, (24 Sept. 2025), Upper Limit on the Non-Gravitational Acceleration and Lower Limits on the Nucleus Mass and Diameter of 3I/ATLAS, arXiv, on line, 2509.21408.
• Farnham, Tony L., et al., 23 Sept. 2025, Observations of an Asymmetric CN Coma in Interstellar Comet 3I/ATLAS, Astronomer's Telegram, 17416, on line, 17416.
• Quanzhi Ye, et al., (10 Sept. 2025), Prediscovery Activity of New Interstellar Object 3I/ATLAS: A Dynamically-Old Comet?, arXiv, on line, 2509.08792.
• Keto, Eric, and Abraham Loeb, (9 Sept. 2025), The Physics of Cometary Anti-tails as Observed in 3I/ATLAS, arXiv, on line, 2509.07771.
• Perez-Couto, X., S. Torres, E. Villaver, A. J. Mustill, and M. Manteiga, (9 Sept. 2025), 3I/ATLAS: In Search of the Witnesses to Its Voyage, arXiv, on line, 2509.06300.
• Trivdei, Oem, and Abraham Loeb, (7 Sept. 2025), Dynamical Constraints on a Population of Massive Interstellar Objects, arXiv, on line, 2509.06300.
• Trivdei, Oem, and Abraham Loeb, (7 Sept. 2025), Quantitative Mapping of the Loeb Scale, arXiv, on line, 2509.06253.
• Ivanova, Oleksandra, et al., 5 Sept. 2025, Follow-up observations of the dust fan ejected from interstellar comet 3I/ATLAS, Astronomer's Telegram, 17372, on line 17372.
• Tonry, John, et al., (5 Sept. 2025), ATLAS Photometry of Interstellar Object 3I/ATLAS, arXiv, on line, 2509.05562.
• Gray, Zuri, et al., (5 Sept. 2025), Extreme Negative Polarisation of New Interstellar Comet 3I/ATLAS, arXiv, on line, 2509.05181.
• Yiyang Guo, et al., (3 Sept. 2025), Search for Past Stellar Encounters and the Origin of 3I/ATLAS, arXiv, on line, 2509.03361.
• Frincke, Tessa T., et al., (2 Sept. 2025), Near-Discovery SOAR Photometry of the Third Interstellar Object: 3I/ATLAS, arXiv, on line, 2509.02813.
• Salazar Manzano, Luis E., et al., (1 Sept. 2025), Onset of CN Emission in 3I/ATLAS: Evidence for Strong Carbon-Chain Depletion, arXiv, on line, 2509.01647.
• Bolin, Bryce, et al., 29 Aug. 2025, The Anti-Solar Tail of Comet 3I/ATLAS Seen in Deep Multi-band Imaging Taken at Gemini South, Astronomer's Telegram, 17363, on line 17363.
• Rahatgaonkar, Rohan, et al., (25 Aug. 2025), VLT 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, arXiv, on line, 2508.18382.
• Cordiner, Martin A., et al., 26 Sept. 2025 (25 Aug. 2025), JWST detection of a carbon dioxide dominated gas coma surrounding interstellar object 3I/ATLAS, Astrophysical Journal Letters, 991(2):L43; arXiv, on line, 2508.18209.
• Schleicher, David, 22 Aug. 2025, The Detection of CN in Interstellar Comet 3I/ATLAS, Astronomer's Telegram, 17352, on line 17352.
• Davenport, James R. A., et al., (22 Aug. 2025), Technosignature Searches of Interstellar Objects, arXiv, on line, 2508.16825.
• Eubanks, T. Marshall, et al., (21 Aug. 2025), 3I/ATLAS (C/2025 N1): Direct Spacecraft Exploration of a Possible Relic of Planetary Formation at "Cosmic Noon", arXiv, on line, 2508.15768.
• Lisse, C. M., et al., Sept. 2025 (24 Aug. 2025), SPHEREx Discovery of Strong Water Ice Absorption and an Extended Carbon Dioxide Coma in 3I/ATLAS, RNAAS, 9(9):242; arXiv, on line, 2508.15469.
• Eldadi, Omer, Gershon Tenenbaum, and Abraham Loeb, (6 Aug. 2025), The Loeb Scale: Astronomical Classification of Interstellar Objects, arXiv, on line, 2508.09167.
• Beniyama, Jin, Sept. 2025 (12 Aug. 2025), Simultaneous visible spectrophotometry of interstellar object 3I/ATLAS with Seimei/TriCCS, Publications of the Astronomical Society of Japan; arXiv, on line, 2508.08829.
• Xing, Zexi, Shawn Oset, John Noonan, and Dennis Bodewits, Oct. 2025 (6 Aug. 2025), Water Production Rates of the Interstellar Object 3I/ATLAS, Astrophysical Journal Letters, 991(2):L50; arXiv, on line, 2508.04675.
• Kakharov, Shokhruz, and Abraham Loeb, (6 Aug. 2025), Galactic Trajectories of Interstellar Objects 1I/'Oumuamua, 2I/Borisov, and 3I/Atlas, arXiv, on line, 2408.02739.
• Jewitt, David, et al, Sept. 2025 (4 Aug. 2025), Hubble Space Telescope Observations of the Interstellar Interloper 3I/ATLAS, Astrophysical Journal Letters, 990(1):L2; arXiv, on line, 2508.02934.
• Puzia, Thomas H., et al., Sept. 2025 (4 Aug. 2025), Spectral Characteristics of Interstellar Object 3I/ATLAS from SOAR Observations, Astrophysical Journal Letters, 990(1):L27; arXiv, on line, 2508.02777.
• Martinez-Palomera, Jorge, et al., (4 Aug. 2025), Pre-discovery TESS Observations of Interstellar Object 3I/ATLAS, arXiv, on line, 2508.02499.
• Santana-Ros, T., et al., (1 Aug. 2025), Temporal Evolution of the Third Interstellar Comet 3I/ATLAS: Spin, Color, Spectra and Dust Activity, arXiv, on line 2508.00808.
• Sanchez, Joan Pau, and Colin Snodgrass, July 2025, Analysis of Trajectories to 3I/ATLAS with a Comet Interceptor-like Spacecraft, RNAAS, 9(7):207, on line at RNAAS.
• Jones, Nicola, July 2025, Rare find: interstellar visitor seen blazing through our Solar System, Nature, 643(8072):620.
• Feinstein, Adina D., John W. Noonan, and Darryl Z. Seligman, Sept. 2025 (29 July 2025), Precovery Observations of 3I/ATLAS from TESS Suggests Possible Distant Activity, Astrophysical Journal Letters, 991(1):L2; arXiv, on line, 2507.21967.
• Loeb, Abraham, Adam Hibberd, and Adam Crowl, (28 July 2025), Intercepting 3I/ATLAS at Closest Approach to Jupiter with the Juno spacecraft, arXiv, on line, 2507.21402.
• Dey, Lankeswar, et al., (25 July 2025), NANOGrav 15-year Data Set: Search for Gravitational Scattering of Pulsars by Free-Floating Objects in Interstellar Space, arXiv, on line, 2507.19475.
• Eldadi, Omer, Gershon Tenenbaum, and Abraham Loeb, (23 July 2025), From Extraterrestrial Microbes to Alien Intelligence: Rebalancing Astronomical Research Priorities, arXiv, on line, 2507.17790.
• Yaginuma, Atsuhiro, et al., (21 July 2025), The Feasibility of a Spacecraft Flyby with the Third Interstellar Object 3I/ATLAS from Earth or Mars, arXiv, on line, 2507.15755.
• Yang, Bin, et al., 6 Oct. 2025 (20 July 2025), Spectroscopic Characterization of Interstellar Object 3I/ATLAS: Water Ice in the Coma, Astrophysical Journal Letters, 992(1):L9; arXiv, on line, 2507.14916.
• Chandler, Colin Orion, et al, (17 July 2025), NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1), arXiv, on line, 2507.13409.
• de la Fuente Marcos, R., et al., Aug. 2025 (17 July 2025), Assessing interstellar comet 3I/ATLAS with the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope, Astronomy and Astrophysics, 700:L9; arXiv, on line, 2507.12922.
• Kareta, Theodore, et al., Sept. 2025 (16 July 2025), Near-Discovery Observations of Interstellar Comet 3I/ATLAS with the NASA Infrared Telescope Facility, Astrophysical Journal Letters, 990(2):L65; arXiv, on line, 2507.12234.
• Hibberd, Adam, Adam Crowl, and Abraham Loeb, (16 July 2025), Is the Interstellar Object 3I/ATLAS Alien Technology?, arXiv, on line, 2507.12213.
• Belyakov, Matthew, et al., July 2025 (15 July 2025), Palomar and Apache Point Spectrophotometry of Interstellar Comet 3I/ATLAS, RNAAS, 9(7):194; arXiv, on line, 2507.11720.
• Bolin, Bryce T., et al., 13 July 2025, Apache Point Observatory Colors of Interstellar Comet 3I/ATLAS, Astronomer's Telegram, 17284, on line 17284.
• Champagne, Chansey, et al., 11 July 2025, Initial Results from NASA/IRTF Observations of Interstellar Comet 3I/ATLAS, Astronomer's Telegram, 17283, on line 17283.
• Taylor, Aster G., and Darryl Z. Seligman, Sept. 2025 (10 July 2025), The Kinematic Age of 3I/ATLAS and its Implications for Early Planet Formation, Astrophysical Journal Letters, 990(1):L14; arXiv, on line, 2507.08111.
• Alvarez-Candal, A., et al., Aug. 2025 (9 July 2025), X-SHOOTER Spectrum of Comet 3I/ATLAS: Insights into a Distant Interstellar Visitor, Astronomy and Astrophysics, 700:L10; arXiv, on line, 2507.07312.
• Loeb, Abraham, July 2025 (8 July 2025), 3I/ATLAS is Smaller or Rarer than It Looks (Comment on "Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS" [arXiv:2507.02757]), RNAAS, 9(7):178; arXiv, on line, 2507.05881.
• Hopkins, Matthew J., et al., Sept. 2025 (7 July 2025), From a Different Star: 3I/ATLAS in the context of the Ōtautahi-Oxford interstellar object population model, Astrophysical Journal Letters, 990(2):L30; arXiv, on line, 2507.05318.
• Belyakov, Matthew, et al., 7 July 2025, Spectral Slope and Colors of Interstellar Comet 3I/ATLAS with the Palomar 200-inch Palomar Next Generation Spectrograph, Astronomer's Telegram, 17276, on line 17276.
• Bolin, Bryce T., et al., Sept. 2025 (7 July 2025), Interstellar comet 3I/ATLAS: discovery and physical description, MNRAS, 542(1):L139-L143; arXiv, on line, 2507.05252.
• Opitom, Cyrielle, et al., Nov. 2025 (7 July 2025), Snapshot of a new interstellar comet: 3I/ATLAS has a red and featureless spectrum, MNRAS, 544(1):L31-L36; arXiv, on line, 2507.05226.
• Minev, M., A. Kostov, and A. Mutafov, 6 July 2025, Follow up observations of interstellar comet 3I/ATLAS, Astronomer's Telegram, 17275, on line 17275; Erratum, 7 July 2025, Astronomer's Telegram, 17278, on line 17278.
• Alarcon, Miguel R., et al., 3 July 2025, Deep g'-band Imaging of Interstellar Comet 3I/ATLAS from the Two-meter Twin Telescope (TTT), Astronomer's Telegram, 17264, on line 17264.
• Seligman, Darryl Z., et al., Aug. 2025 (3 July 2025), Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS, Astrophysical Journal Letters, 989(2):L36; arXiv, on line, 2507.02757.

--other items on 3I/ATLAS (from newest to oldest)

• ESA, 7 Oct. 2025, ESA's ExoMars and Mars Express observe comet 3I/ATLAS, ESA, on line https://www.esa.int/Science_Exploration/Space_Science/ESA_s_ExoMars_and_Mars_Express_observe_comet_3I_ATLAS.
• NASA, 2 Oct. 2025, Comet 3I/ATLAS, NASA, on line https://science.nasa.gov/solar-system/comets/3i-atlas/.
• Planetary Society, 22 Sept. 2025, Studying a distant visitor: What we know about Interstellar Object 3I/ATLAS, Planetary Society, on line https://www.planetary.org/articles/studying-a-distant-visitor-what-we-know-about-interstellar-object-3i-atlas.
• Gilster, Paul, 6 Sept. 2025, 3I/ATLAS: The Case for an Encounter, Centauri Dreams, on line https://www.centauri-dreams.org/2025/09/06/3i-atlas-the-case-for-an-encounter/.
• NOIRLab, 4 Sept. 2025, Gemini South Captures Growing Tail of Interstellar Comet 3I/ATLAS During Educational Observing Program, NOIRLab, on line https://noirlab.edu/public/news/noirlab2525/.
• O'Callaghan, Jonathan, 17 July 2025, 7 Big Mysteries about Interstellar Object 3I/ATLAS, Scientific American, on line https://www.scientificamerican.com/article/new-interstellar-object-3i-atlass-biggest-mysteries-explained/.
• Gilster, Paul, 16 July 2025, A Better Look at 3I/ATLAS, Centauri Dreams, on line https://www.centauri-dreams.org/2025/07/16/a-better-look-at-3i-atlas/.
• Gilster, Paul, 10 July 2025, 3I/ATLAS: Observing and Modeling an Interstellar Newcomer, Centauri Dreams, on line https://www.centauri-dreams.org/2025/07/10/3i-atlas-observing-and-modeling-an-interstellar-newcomer/.
• NASA, 2 July 2025, NASA Discovers Interstellar Comet Moving Through Solar System, NASA, on line https://science.nasa.gov/blogs/planetary-defense/2025/07/02/nasa-discovers-interstellar-comet-moving-through-solar-system/.

--Minor Planet Center releases on 3I/ATLAS

• MPC, 8 Oct. 2025, Comet 3I/ATLAS, MPEC 2025-T133.
• MPC, 8 Sept. 2025, Comet 3I/ATLAS, MPEC 2025-R63.
• MPC, 28 July 2025, Comet 3I/ATLAS, MPEC 2025-O116.
• MPC, 25 July 2025, Comet 3I/ATLAS, MPEC 2025-O84.
• MPC, 23 July 2025, Comet 3I/ATLAS, MPEC 2025-O71.
• MPC, 21 July 2025, Comet 3I/ATLAS, MPEC 2025-O40.
• MPC, 18 July 2025, Comet 3I/ATLAS, MPEC 2025-O20.
• MPC, 16 July 2025, Comet 3I/ATLAS, MPEC 2025-O05.
• MPC, 14 July 2025, Comet 3I/ATLAS, MPEC 2025-N102.
• MPC, 11 July 2025, Comet 3I/ATLAS, MPEC 2025-N89.
• MPC, 6 July 2025, Comet 3I/ATLAS, MPEC 2025-N51.
• MPC, 5 July 2025, Comet 3I/ATLAS, MPEC 2025-N44.
• MPC, 4 July 2025, Comet 3I/ATLAS, MPEC 2025-N35.
• MPC, 3 July 2025, Comet 3I/ATLAS, MPEC 2025-N22.
• MPC, 2 July 2025, 3I/ATLAS = C/2025 N1, MPEC 2025-N12.

--International Astronomical Union releases on 3I/ATLAS

• MPC, 12 Dec. 2025, Comet 3I/ATLAS, CBET 5646.
• MPC, 23 Nov. 2025, Comet 3I/ATLAS, CBET 5640.
• MPC, 30 Oct. 2025, Comet 3I/ATLAS, CBET 5628.
• MPC, 21 Oct. 2025, Comet 3I/ATLAS, CBET 5625.
• MPC, 18 Sept. 2025, Comet 3I/ATLAS, CBET 5608.
• MPC, 20 Aug. 2025, Comet 3I/2025 N1 (ATLAS), CBET 5596.
• MPC, 2 July 2025, Comet C/2025 N1 (ATLAS) = 3I/ATLAS, CBET 5578.

--background articles and data sets

• see page on for background on hyperbolic/near hyperbolic comets.

Comments? Questions? Corrections? Contact me.
Last modified 17 May 2026.
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