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Mean reflectance spectrum of 3I/ATLAS, co-added from the nights of August 10, 12, 16, and 17 with the two.4 m MDM telescope (black). For comparability, we present the spectra of 3I/ATLAS reported by D. Z. Seligman et al. (2025) (yellow), obtained on July 4 with the two.2 m UH telescope, and the D-type spectral taxonomy from F. E. DeMeo et al. (2009) (blue). Squares mark photometric measurements obtained with the 1.3 m MDM telescope. Vertical strains mark the positions of typical cometary emission options: CN at 3870 ˚A, C3 at 4050 ˚A, C2(∆ν = 1) at 4750 ˚A, and C2(∆ν = 0) at 5150 ˚A. — astro-ph.EP
Interstellar objects present a direct window into the environmental circumstances round stars aside from the Sun.
The current discovery of 3I/ATLAS, the second interstellar comet ever noticed, affords a singular alternative to research the bodily and chemical properties of interstellar objects and to check them with these of comets in our personal Solar System.
In this Letter we current the outcomes of a 10-night spectroscopic and photometric monitoring marketing campaign with the two.4 m Hiltner and 1.3 m McGraw-Hill telescopes on the MDM Observatory. The marketing campaign was carried out between August 8 and 17 whereas 3I/ATLAS was inbound at heliocentric distances of three.2 – 2.9 au. Our observations captured the onset of optical gas-driven exercise.
Nightly spectra reveal a weak CN emission function within the coma of 3I/ATLAS, absent in the course of the first nights however steadily strengthening thereafter. We measure a CN manufacturing price of ∼8×1023 s−1, in the direction of the decrease finish of exercise noticed in Solar System comets. Simultaneous photometry additionally signifies a small however measurable enhance within the coma’s radial profile and rising r-band Afρ with values within the order of ∼300 cm.
Our higher restrict on the C2-to-CN ratio (logQ(C2)/Q(CN)<−1.05) locations 3I/ATLAS among the many most carbon-chain depleted comets recognized. The derived gas-to-dust manufacturing ratio of logQ(CN)/Afρ<21.49 is likewise on the low finish of the Solar System comet distribution.
Further observations of 3I/ATLAS are required to confirm the obvious carbon-chain depletion and to discover whether or not such composition represents a recurring trait of the interstellar comet inhabitants.
Luis E. Salazar Manzano, Hsing Wen Lin, Aster G. Taylor, Darryl Z. Seligman, Fred C. Adams, David W. Gerdes, Thomas Ruch, Tessa T. Frincke, Kevin J. Napier
Comments: Submitted to The Astrophysical Journal Letters (ApJL). 12 pages, 5 figures, and three tables
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2509.01647 [astro-ph.EP] (or arXiv:2509.01647v1 [astro-ph.EP] for this model)
https://doi.org/10.48550/arXiv.2509.01647
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Submission historical past
From: Luis Salazar Manzano
[v1] Mon, 1 Sep 2025 17:46:53 UTC (1,990 KB)
Astrobiology
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