Zitat Apache Point Observatory Colors of Interstellar Comet 3I/ATLAS on 13 Jul 2025; 17:27 UT Credential Certification: Bryce Bolin (bolin.astro@gmail.com)
We report color measurements of interstellar comet 3I/ATLAS from g, r, i, and z band photometry taken with the Astrophysical Research Consortium 3.5-m telescope (ARC 3.5-m) at Apache Point Observatory (observatory code 705). We used the ARC Telescope Imaging Camera (ARCTIC) to observe 3I/ATLAS on 2025 July 06 03:23 UTC. The comet appears to be extended in the ARCTIC images, with a coma having a FWHM between 1.8-2.3 arcsec in the g, r, i, and z images compared to the FWHM measured for nearby background stars of ~1.5 arcsec (see attached g, r, i, and z-band band image composite), confirming the results of recent ATels: ATel #17263 (Jewitt & Luu), ATel#17264 (Alacron et al.), ATel #17275 (Minev et al.), and ATel #17276 (Belyakov et al.). Using our multi-band images, we measured the following color indices using an aperture with a 4.1 arcsec, equivalent to 10,000 km at the 3.36 au geocentric distance of the comet: g-r = 0.81 +/- 0.06, r-i = 0.18+/-0.04, i-z = -0.02+/-0.07, and g-i = 0.99+/-0.08, equivalent to a spectral slope of 15.5+/-2.6 % / 100 nm. The r-i measurement made with the ARC 3.5-m/ARCTIC appears to be equivalent to the r-i measurement from photometry and spectroscopy described by Belyakov et al. in ATel #17276 of r-i = 0.16+/-0.02. However, our g-r measurement is significantly more red (g-r = 0.81 +/- 0.06 vs. g-r = 0.43 +/- 0.02). The g-r and overall color slope measured with the ARC 3.5/ARCTIC appear to be in line with the spectral slope measurements for the comet reported in other recent results (e.g., ATel #17283 by Champagne et al.). Based on observations obtained with the Apache Point Observatory 3.5-meter telescope, which is owned and operated by the Astrophysical Research Consortium.
FWHM steht für "Full Width at Half Maximum" und wird zur Abgabe des Seeing, der atmosphärischen Sichtbedingungen, verwendet. Es bezeichnet die Breite (bzw. "Verschmierung") des einfallenden Lichts bei der Hälfte der maximalen Helligkeit. Je kleiner der Wert, desto punktschärfer erfolgt die Abbildung.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Image Credit: Gemini Observatory/NOIRLab/NSF/AURA/K. Meech (IfA/U. Hawaii) Processing: Jen Miller, Mahdi Zamani (NSF/NOIRLab)
Also known as C/2025 N1, 3I/ATLAS is clearly a comet, its diffuse cometary coma, a cloud of gas and dust surrounding an icy nucleus, is easily seen in these images from the large Gemini North telescope on Maunakea, Hawai‘i. The left panel tracks the comet as it moves across the sky against fixed background stars in successive exposures. Three different filters were used, shown in red, green, and blue. In the right panel the multiple exposures are registered and combined to form a single image of the comet.
Die gleiche Aufnahme des Gemini-North-Telescope auf dem Maunakea (anscheinend ist die Schreibweise in den letzten Jahren geändert worden), mit einem Hauptspiegel-⌀ von 8,1 m, vom 15. Juli in höherer Auflösung (1800 x 1800 Pixel): https://upload.wikimedia.org/wikipedia/c...22c%29.tiff.jpg
RE: JWST, HST
Zitat Astronomers race to study interstellar interloper
Phalanx of instruments scrutinize 3I/ATLAS for clues about planet formation elsewhere in the galaxy 11 Jul 20259:00 AM ET
The main thing scientists want to figure out is 3I/ATLAS’s composition. Comets and asteroids represent the leftovers of planet formation—making ATLAS a discarded sample of alien worlds, flung out from the dusty disk surrounding a distant star. By comparing its ratios of things such as carbon monoxide, water, ammonia, and salts with those of our local comets and asteroids, researchers hope to learn whether other planetary systems have ingredients like our own. “If we see that this building block looks like all the building blocks in our Solar System, that’s good news,” says Karen Meech, an astronomer at the University of Hawaii at Manoa. “That’s encouraging for the potential for life” elsewhere in the Galaxy.
Already ATLAS appears to have a reddish color, which means its surface probably contains organic materials such as methane, typical for both comets in our Solar System and ‘Oumuamua and Borisov. More detail is likely to come as larger instruments such as the Hubble Space Telescope and JWST swing into action. A team of astronomers has submitted a request to target the object with JWST next month. Noonan has sent a similar proposal to Hubble, with the goal of observing 3I/ATLAS near the beginning of December.
Zitat "Assessing interstellar comet 3I/ATLAS with the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope"
Based on observations made with the Gran Telescopio Canarias (GTC) telescope (program ID 62-GTC55/24B), in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (IAC), and the Two-meter Twin Telescope (TTT, PEI project PLANETIX25), in the Spanish Observatorio del Teide of the IAC.
R. de la Fuente Marcos et al., 17 Jul 2025
(Received 16 July 2025)
Abstract
Methods. We identified the spectral type of 3I/ATLAS from the visible reflectance spectrum and used photometric observations to derive its level of activity and rotational properties. Observational data were obtained with the OSIRIS camera spectrograph at the 10.4 m Gran Telescopio Canarias and the Two-meter Twin Telescope. We used N-body simulations and statistical analyses of Gaia DR3 data to investigate the origin of 3I/ATLAS and its Galactic background.
Results. Interstellar comet 3I/ATLAS has a visible spectrum consistent with that of a D-type asteroid, and has a spectral slope S′=14.6±0.2 %/1000 Å in the 5000–9000 Å range, which is similar to the one of ‘Oumuamua but redder than that of 2I/Borisov and most solar system comets. It has a conspicuous coma and its rotation period is 16.79±0.23 h. The heliocentric components of its Galactic velocity were (U,V,W)=(−51.25±0.02,−19.466±0.011,+18.94±0.014) km s-1 with a radiant in Sagittarius (295.∘050±0.∘008, −19.∘0693±0.∘0012). The analysis of a sample of kinematic analogs of 3I/ATLAS extracted from Gaia DR3 suggests that its parent system is part of the Galactic thin disk and includes a solar-like star with slightly sub-solar metallicity.
Conclusions. The results from the physical characterization of 3I/ATLAS further support the idea that extrasolar debris is not too different from the one found in the solar system and it is the result of similar formation processes.
Mein Beitrag fußt noch auf der Annahme, daß das Ursprungssystem in der Dicken Scheibe der Milchstraße lag/liegt. Wenn die chemische Zusammensetzung an schwereren Elementen nur knapp unter der des solaren Urnebels liegt, dann wäre damit wohl auch die Annahme, er sei erheblich älter als das Sonnensystem, hinfällig. Ein schönes Beispiel für den dynamischen Wissenszuwachs durch Empirie. Aus dem Paper:
Zitat Considering Nissen (2004), fig. 1.3, the components of the solar-motion corrected heliocentric Cartesian velocities of 3I/ATLAS place it in the thin disk as the value of (ULSR2+WLSR2)1/2 is 67.68 km s-1 and VLSR=−7.2 km s-1. The Toomre diagram indicates that the thin disk is inside (ULSR2+WLSR2)1/2< 85 km s-1 with the thick disk in the interval (85, 180) km s-1 and the halo outside 180 km s-1. In addition to this kinematic constraint, the analysis of a sample of kinematic analogues of 3I/ATLAS from Gaia DR3 gives a value of [Fe/H]=−0.04±0.14 (see Appendix F), which is somewhat sub-solar, but far from −1.2<[Fe/H]<−0.4 in the thick disk (see, e.g., Nissen 2004). An origin in the thick disk is favored by Hopkins et al. (2025).
Wie im Abstract angegeben, liegt der Radiant bei 19h67m R.A. und -19,06° Dekl. Das galaktische Zentrum liegt bei -17h45m40s R.A. und -29°0'26,95" Dekl.
"Les hommes seront toujours fous; et ceux qui croient les guérir sont les plus fous de la bande." - Voltaire
Zitat SPHEREx Discovers Extended Carbon Dioxide Coma in Interstellar Object 3I-ATLAS News Release • August 21st, 2025
SPHEREx has made detailed multi-spectral observations of interstellar comet 3I/ATLAS, detecting an abundance of carbon dioxide gas in its coma (the extended gaseous atmosphere of a comet) and water ice in its nucleus. The observations were made between Aug. 8 to Aug. 12, when the object was about 290 million miles (470 million kilometers) from the Sun. This discovery highlights SPHEREx unique capabilities: its spectral resolution allowed us to clearly detect the CO2 emission, while its wide field of view enabled us to map the coma over scales extending 10 arminutes. SPHEREx published a brief Research Notice of the American Astronomical Society, and plans to releave a more detailed publication soon.
Although further observations are needed to fully understand the interstellar object’s composition — many other NASA missions will be attempting to observe 3I/ATLAS as well — the discovery of an extended CO2 coma and the abundance of ice water shows that 3I/ATLAS may not be so different from the comets that formed around our Sun. Interstellar objects can provide scientists with a better understanding about the chemistry of star systems many light-years away.
Zitat James Webb Space Telescope takes 1st look at interstellar comet 3I/ATLAS with unexpected results
By Robert Lea published 6 hours ago
NASA's $10 billion space telescope studied the third interstellar object to enter the solar system, measuring the chemical contents of its halo.
The James Webb Space Telescope (JWST) has observed the interstellar visitor 3I/ATLAS for the first time. The powerful space telescope trained its infrared vision and its Near-Infrared Spectrograph instrument (NIRspec) on the comet on Aug. 6, 2025.
In a preprint paper describing their investigation of 3I/ATLAS, a team of astronomers that observed the comet with the JWST explains that studying comets like this from other star systems helps to study what conditions were like in those systems as they were forming. Those results can then be compared to what scientists have learned about the conditions around the sun 4.6 billion years ago, when the planets, asteroids, and comets of the solar system were forming.
As expected, 3I/ATLAS is outgassing as it approaches the sun, and astronomers have used the JWST and its NIRSpec instrument to identify carbon dioxide, water, water ice, carbon monoxide, and the smelly gas carbonyl sulfide in its coma.
What wasn't expected, however, was the highest ratio of carbon dioxide to water ever observed in a comet. This could reveal more about the conditions in which 3I/ATLAS formed.
The abundance of carbon dioxide in the coma of 3I/ATLAS could indicate that the interstellar comet has a heart that is intrinsically rich in carbon dioxide. This could imply that the comet contains ices that were exposed to much higher levels of radiation than comets in the solar system have been exposed to.
Alternatively, the team suggests this high carbon dioxide content could indicate that 3I/ATLAS may have formed in a specific site called the "carbon dioxide ice line" within the swirling cloud of matter, or "protoplanetary disk," that surrounded its stellar parent. This is defined as the point at which the temperature around an infant star or "protostar" falls low enough to allow carbon dioxide to change from a gas to a solid.
Furthermore, the low abundance of water vapor in the coma of 3I/ATLAS could indicate that there is something within the comet that is inhibiting heat from penetrating the icy core of the comet. This would hinder the amount of water transforming from ice into gas relative to the transformation rate of carbon dioxide and carbon monoxide.
Zitat In astronomy or planetary science, the frost line, also known as the snow line or ice line, is the minimum distance from the central protostar of a solar nebula where the temperature is low enough for volatile compounds such as water, ammonia, methane, carbon dioxide and carbon monoxide to condense into solid grains, which will allow their accretion into planetesimals. Beyond the line, otherwise gaseous compounds (which are much more abundant) can be quite easily condensed to allow formation of gas and ice giants; while within it, only heavier compounds can be accreted to form the typically much smaller rocky planets.
The term itself is borrowed from the notion of "frost line" in soil science, which describes the maximum depth from the surface that groundwater can freeze.
Each volatile substance has its own frost line (e.g. carbon monoxide,[1] nitrogen,[2] and argon[3]), so it is important to always specify which material's frost line is referred to, though omission is common, especially for the water frost line. A tracer gas may be used for materials that are otherwise difficult to detect; for example diazenylium for carbon monoxide.
Location Different volatile compounds have different condensation temperatures at different partial pressures (thus different densities) in the protostar nebula, so their respective frost lines will differ. The actual temperature and distance for the snow line of water ice depend on the physical model used to calculate it and on the theoretical solar nebula model:
170 K at 2.7 AU (Hayashi, 1981)[4] 143 K at 3.2 AU to 150 K at 3 AU (Podolak and Zucker, 2010)[5] 3.1 AU (Martin and Livio, 2012)[6] ≈150 K for μm-size grains and ≈200 K for km-size bodies (D'Angelo and Podolak, 2015)[7] The location of the frost line changes over time, potentially reaching a maximum radius of 17.4 AU for a solar-mass star before decreasing thereafter.[8] ... Observations of the asteroid belt, located between Mars and Jupiter, suggest that the water snow line during formation of the Solar System was located within this region. The outer asteroids are icy C-class objects (e.g. Abe et al. 2000; Morbidelli et al. 2000) whereas the inner asteroid belt is largely devoid of water. This implies that when planetesimal formation occurred the snow line was located at around 2.7 AU from the Sun.
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