Tootfinder

☄️ Comet #3I/ATLAS is currently making its closest approach to the Sun.
#ESAJuice might catch the best view of this comet in a very active state. Juice will attempt observations in November 2025, with data received on Earth in February 2026
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Comet 3I/ATLAS – frequently asked questions
Note that this list is regularly updated as we learn more about comet 3I/ATLAS

ESA’s space probe #JUICE is headed towards a truly unexpected encounter: on November 2nd, observations of interstellar object #3IATLAS will begin. Read more about contributions from #mpsgoettingen

And here comes ... another light curve of interstellar comet #ATLAS through much of October, now based on the satellite coronagraphs LASCO C3 and CCOR-1, with observations up to and including October 26th! From the paper "Rapid Brightening of 3I/ATLAS Ahead of Perihelion" - https://arxiv.org/abs/2510.25035 - out minutes ago: it finds that "CCOR-1 also resolves the comet as an extended source with an apparent coma ~4' in diameter. Furthermore, LASCO color photometry shows the comet to be distinctly bluer than the Sun, consistent with gas emission contributing a substantial fraction of the visible brightness near perihelion."

Keine Außerirdischen: NASA zeigt Bilder von 3I/ATLAS
Nach dem Ende des Shutdowns hat die NASA endlich Bilder des Kometen 3I/ATLAS gezeigt. Das lange Schweigen der Raumfahrtbehörde hatte zu Spekulationen geführt.
https:…

3I/ATLAS: Auch chinesische Marssonde fotografiert interstellaren Kometen
Weil die größte Annäherung von 3I/ATLAS an die Sonne von der Erde aus nicht sichtbar war, mussten Sonden einspringen. Das hat auch eine aus China getan.

All the NASA s/c images of #3IATLAS shared today (and some more) can be found at https://science.nasa.gov/solar-system/comets/3i-atlas/comet-3i-atlas-image-gallery/ now - including this spectrum from the Imaging Ultraviolet Spectrograph on MAVEN taken on 28 September, showing hydrogen emitted from different sources, namely the comet (dim spot on the far left), hydrogen from Mars (bright emission on the right), and hydrogen flowing through our solar system between the planets (dim emission in the middle).

Astronomie: ESA-Missionen fotografieren 3I/ATLAS, die der NASA vielleicht auch
Der interstellare Komet 3I/ATLAS hat den Mars passiert und Sonden haben versucht, ihn zu fotografieren. Die ESA zeigt die Bilder, bei der NASA muss man suchen.

All eyes on #3I/ATLAS ☄️
Our Mars Express & ExoMars Trace Gas Orbiter will observe the comet around its closest approach to Mars on 3 October 2025, when 3I/ATLAS will be around 30 million km from the red planet.

ESA observations of interstellar comet 3I/ATLAS
The European Space Agency (ESA) reacted promptly to the discovery of comet 3I/ATLAS on 1 July 2025. Soon after they were alerted to its existence by automated detection systems, ESA astronomers began using ground-based telescopes in Hawaii, Chile, and Australia to monitor its progress.Since then, the comet has been observed by space telescopes close to Earth, including the NASA/ESA Hubble Space Telescope and the NASA/ESA/CSA James Webb Space Telescope.In the coming months, ESA will turn interp…

Spatial Profiles of 3I/ATLAS CN and Ni Outgassing from Keck/KCWI Integral Field Spectroscopy
W. B. Hoogendam, B. J. Shappee, J. J. Wray, B. Yang, K. J. Meech, C. Ashall, D. D. Desai, K. Hart, J. T. Hinkle, A. Hoffman, E. M. Hu, D. O. Jones, K. Medler
https://arxiv.org/abs/2510.11779

Spatial Profiles of 3I/ATLAS CN and Ni Outgassing from Keck/KCWI Integral Field Spectroscopy
Cometary activity from interstellar objects provides a unique window into the environs of other stellar systems. We report blue-sensitive integral field unit spectroscopy of the interstellar object 3I/ATLAS from the Keck-II-mounted Keck Cosmic Web Imager on August 24, 2025 UT. We confirm previously reported CN and Ni outgassing, and present, for the first time, the radial profiles of Ni and CN emission in 3I/ATLAS. We find a characteristic $e$-folding radius of $593.7\pm14.8$ km for Ni and $841…

And here is now also a spectrum of #comet #3I/ATLAS taken during the #ShadowTheScientists session on 26 November, from https://www.astronomerstelegram.org/?read=17561 - CN (388 nm), C3 (402 nm) and C2 (474 nm/517 nm) are detected. Meanwhile the paper https://arxiv.org/abs/2512.18341 concludes from the non-gravitational acceleration that the diameter of the comet's nucleus is 820 to1050 m.

Interstellarer Komet 3I/ATLAS: Jetzt sind die Weltraumsonden dran
Der interstellare Besucher 3I/ATLAS rast weiter durchs Sonnensystem, von der Erde aus ist er aber gerade nicht zu sehen. Deshalb übernehmen jetzt Raumsonden.

Interstellar Comet 3I/ATLAS Stuns Scientists with Surprising Bright Outburst and Ancient Origins https://ground.news/article/interstellar-comet-3i-atlas-stuns-scientists-with-surprising-bright-outburst-and-ancient-origins_cafba4

Astronomie: Interstellarer Komet 3I/ATLAS wieder von der Erde aus sichtbar
Ein Astronom aus den USA hat in den frühen Morgenstunden mehrere Aufnahmen des interstellaren Kometen 3I/ATLAS gemacht. Er war vorher nicht für uns sichtbar.

#3iatlas
I've read that we can't observe 3I/Atlas from earth because it will be behind the sun, but according to SkyLive it looks like i should be possible to spot it from Norway still at around 1730.
If I had had a telescope, I would have tried(and likely failed).
#3i_atlas

The size of #3I/ATLAS from non-gravitational acceleration: https://arxiv.org/abs/2512.18341 -> "we find diameters between 820 meters and 1050 meters [...] reliable estimates of the mass loss rate at other stages of the comet's trajectory will substantially reduce the systematic uncertainty in this estimate."

Non-Gravitational Acceleration in 3I ATLAS: Constraints on Exotic Volatile Outgassing in Interstellar Comets
Florian Neukart
https://arxiv.org/abs/2511.07450 https://arxiv.org/pdf/2511.07450 https://arxiv.org/html/2511.07450
arXiv:2511.07450v1 Announce Type: new
Abstract: The interstellar comet 3I/ATLAS exhibited a measurable nongravitational acceleration similar in form to that of 1I/'Oumuamua but of smaller magnitude. Using thermophysical and Monte Carlo models, we show that this acceleration can be fully explained by anisotropic outgassing of conventional volatiles, primarily CO and CO2, under realistic surface and rotational conditions. The model includes diurnal and obliquity-averaged energy balance, empirical vapor-pressure relations, and collimated jet emission from localized active regions. Mixed CO-CO2 compositions reproduce both the magnitude and direction of the observed acceleration with physically plausible active fractions below one percent for nucleus radii between 0.5 and 3 km. Less volatile species such as NH3 and CH4 underproduce thrust at equilibrium temperatures near 1 AU. These results eliminate the need for nonphysical or exotic explanations and define thermophysical limits for natural acceleration mechanisms in interstellar comets.
toXiv_bot_toot

Or friend @… seems to be getting a wee bit exhasperated with all the silly people that are saying nonsense about 3I Atlas. :) https://youtu.be/O0Q4agPyUqI

Crosslisted article(s) found for astro-ph.SR. https://arxiv.org/list/astro-ph.SR/new
[1/1]:
- Spatial Profiles of 3I/ATLAS CN and Ni Outgassing from Keck/KCWI Integral Field Spectroscopy
Hoogendam, Shappee, Wray, Yang, Meech, Ashall, Desai, Hart, Hinkle, Hoffman, Hu, Jones, Medler

Finally an RGB image of comet #3IATLAS from images taken by #GeminiNorth during the 26 November #shadowTheScientists session: https://noirlab.edu/public/news/noirlab2532/ - the coma has become bluer due to more gas emission. Also published today: an X-ray image by XMM-Newton at https://www.esa.int/ESA_Multimedia/Images/2025/12/XMM-Newton_sees_comet_3I_ATLAS_in_X-ray_light with explanations in http://www.cbat.eps.harvard.edu/iau/cbet/005600/CBET005646.txt which also contains more 3I news.
Meanwhile the paper https://iopscience.iop.org/article/10.3847/2515-5172/ae2915 claims an upper limit for 3I's nucleus diameter of only some 750 meters from the measured non-gravitational acceleration (NGA) parameters: that would be waaay more stringent than the 5.6 km upper limit from early Hubble observations reported in https://iopscience.iop.org/article/10.3847/2041-8213/adf8d8 (where also a lower limit of 440 meters is stated).

JCMT detection of HCN emission from 3I/ATLAS at 2.1 AU
Iain M. Coulson, Yi-Jehng Kuan, Steven B. Charnley, Martin A. Cordiner, Yo-Ling Chuang, Yueh-Ning Lee, Min-Kai Lin, Stefanie N. Milam, Bannawit Pimpanuwat, Nathan X. Roth, Micha{\l} \.Z\'o{\l}towski
https://arxiv.org/abs/2510.02817

JCMT detection of HCN emission from 3I/ATLAS at 2.1 AU
We report the detection of HCN ($J=3-2$) rotational emission from comet 3I/ATLAS at a heliocentric distance of 2.13 AU with the James Clerk Maxwell Telescope (JCMT). Observations were conducted from 07 August 2025 (UT) using the $^{\prime}\overline U^{\prime}\overline u$ heterodyne receiver and ACSIS spectroscopic backend. The HCN line was detected at $>5σ$ on 14 Sep 2025 (UT) and a production rate of $Q({\rm HCN})=(4.0\pm1.7)\times10^{25}\ {\rm s}^{-1}$ was derived by non-LTE radiative transf…

Our solar system’s interstellar interloper, 3I/ATLAS,
showed strong ultraviolet emissions that are unmistakable telltales of hydroxyl gas (OH), a byproduct of water,
when astronomers imaged it with the with NASA’s Neil Gehrels Swift space telescope before it disappeared behind the Sun.
Their findings, detailed in a new studypublished in The Astrophysical Journal Letters, argue that the presence of all this OH indicates
the comet is ejecting water vapor at a torrentia…

Comparative Analysis of Polarization in Interstellar Comet #3I/ATLAS with Distant Solar System Comets: https://iopscience.iop.org/article/10.3847/2515-5172/ae0d91 > interview with the first author: https://www.youtube.com/watch?v=F30vaWKywpA

Extreme NiI/FeI abundance ratio in the coma of the interstellar comet 3I/ATLAS
Damien Hutsem\'ekers, Jean Manfroid, Emmanu\"el Jehin, Cyrielle Opitom, Michele Bannister, Juan Pablo Carvajal, Rosemary Dorsey, K Aravind, Baltasar Luco, Brian Murphy, Thomas H. Puzia, Rohan Rahatgaonkar
https://arxiv.org/abs/2509.26053

Extreme NiI/FeI abundance ratio in the coma of the interstellar comet 3I/ATLAS
Emission lines of FeI and NiI are commonly found in the coma of solar system comets, even at large heliocentric distances. These atoms are most likely released from the surface of the comet's nucleus or from a short-lived parent. The presence of these lines in cometary spectra is unexpected because the surface blackbody equilibrium temperature is too low to allow the sublimation of refractory minerals containing these metals. These lines were also found in the interstellar comet 2I/Borisov whic…

Simultaneously NASA and ESA have published new spacecraft images of #3IATLAS, https://science.nasa.gov/blogs/3iatlas/2025/12/04/nasas-hubble-space-telescope-revisits-interstellar-comet/ from the Hubble Space Telescope on 30 November (just the inner coma with a central condensation) and https://www.esa.int/ESA_Multimedia/Images/2025/12/Comet_3I_ATLAS_shows_activity_in_Juice_navigation_camera_teaser from Juice's NavCam on 2 November with an early sighting of the plasma tail - more contributions to understanding the behavior of the interstellar visitor.

X-ray observation of the cometary interloper C/2025 N1 (3I/ATLAS) by XRISM/Xtend: #3IATLAS from beyond the solar system: https://www.xrism.jaxa.jp/en/topics/news/1208/