Comets and Asteroids

Potential Thermal Profiles of The Third Interstellar Object 3I/ATLAS

By Keith Cowing

Status Report

astro-ph.EP

November 3, 2025

Filed under 3I/ATLAS, astro-ph.EP, Comet, icy world, Interstellar, organic chemistry, Spectroscopy

Potential Thermal Profiles of The Third Interstellar Object 3I/ATLAS — The temperature versus depth and time for 𝜅 = 10⁻⁴ W m⁻¹ K⁻¹ , 10⁻³ W m⁻¹ K⁻¹, and 10⁻² W m⁻¹ K⁻¹ (top, middle, and bottom panels). The sublimation temperatures of CO (30 K, dash), CO₂ (80 K, dash-dot), and H₂O (150 K, dot) are shown as white contours. The depth of heat penetration and volatile activation strongly depends on the thermal conductivity 𝜅. Note that the range of the 𝑦-axis is different for each panel. — astro-ph.EP

We investigate the thermal evolution of 3I/ATLAS, the third macroscopic interstellar object discovered on 2025 July 1.

By comparing modeled thermal profiles with observations of volatile activity, it is possible to constrain bulk physical properties of a cometary nucleus. 3I/ATLAS is actively producing a variety of cometary volatiles. In this paper, we calculate one-dimensional thermal profiles of the third interstellar object 3I/ATLAS throughout its trajectory in an attempt to gain insight into its bulk properties based on measurements of its volatiles.

Assuming a variety of typical comet and asteroid bulk geophysical properties such as heat capacities, densities, and conductivities, we calculate the radial thermal profile as a function of depth throughout the hyperbolic trajectory. The methods and code to generate the thermal profile are flexible for any hyperbolic or bound orbit. The thermal profiles are benchmarked to the nominal sublimation temperatures of H₂O, CO₂ and CO, but are still applicable to any volatile.

Comparison between the modeled surface temperatures and the observed onset of H₂O activity near 3 au indicates that surface temperatures exceeding ∼150 K can only be achieved if the albedo is below 0.2. We therefore set the upper limit on the albedo of 3I/ATLAS to be 0.2.

Atsuhiro Yaginuma, Aster G. Taylor, Darryl Z. Seligman

Comments: 8 pages, 6 figures, 1 table, submitted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2510.25945 [astro-ph.EP] (or arXiv:2510.25945v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2510.25945
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Submission history
From: Atsuhiro Yaginuma
[v1] Wed, 29 Oct 2025 20:44:49 UTC (539 KB)
https://arxiv.org/abs/2510.25945
Astrobiology, Astrochemistry, Astrogeology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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