Origin and evolution of NiI and FeI in the coma of the interstellar comet 3I/ATLAS throughout its trajectory
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| Auteurs principaux: | , , , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866914543831089152 |
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| author | Hutsemékers, Damien Manfroid, Jean Opitom, Cyrielle Jehin, Emmanuël Krishnakumar, Aravind Fernandes, Fernando Massa Bannister, Michele Bodewits, Dennis Dorsey, Rosemary La Forgia, Fiorangela Murphy, Brian |
| author_facet | Hutsemékers, Damien Manfroid, Jean Opitom, Cyrielle Jehin, Emmanuël Krishnakumar, Aravind Fernandes, Fernando Massa Bannister, Michele Bodewits, Dennis Dorsey, Rosemary La Forgia, Fiorangela Murphy, Brian |
| contents | We present high-resolution UVES+VLT observations of neutral nickel and iron atoms in the coma of the interstellar comet 3I/ATLAS taken after perihelion. Metal emission was strong shortly after perihelion and persisted at large heliocentric distances. At $r_h \sim 2$ au the total metal production rate was found to be at least an order of magnitude larger than that of typical solar-system comets. Post-perihelion production rates exhibit pronounced asymmetry compared to the pre-perihelion behavior: production rates are higher after perihelion and decline more gradually with $r_h$, the difference being stronger for FeI. The NiI/FeI abundance ratio, initially anomalously large before perihelion, evolved toward values comparable to solar-system comets near 2 au, and shows a weaker $r_h$ dependence after perihelion. To interpret these results, we revisited and extended the carbonyl hypothesis in which FeI and NiI are produced by the rapid photodissociation of Fe(CO)$_5$ and Ni(CO)$_4$ vaporized from the nucleus. Fits that include direct sublimation of carbonyls reproduce the observed rates and the high NiI/FeI line ratio, which is determined by the higher volatility of Ni(CO)$_4$. Desorption of carbonyls from sublimating CO$_2$ and H$_2$O ices is found to be negligible. The temperature profiles needed to reproduce the observations were found to be shallower than the equilibrium $T \propto r_h^{-1/2}$ relation, suggesting that the sublimation could occur below the surface of the nucleus. Fits using temperature profiles from thermal models require sublimation from depths of several cm, especially post-perihelion. An additional transient heat source ($T \simeq$ 100-140~K), possibly linked to the amorphous-crystalline ice transition, is proposed to explain the early NiI excess before perihelion. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2605_07652 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Origin and evolution of NiI and FeI in the coma of the interstellar comet 3I/ATLAS throughout its trajectory Hutsemékers, Damien Manfroid, Jean Opitom, Cyrielle Jehin, Emmanuël Krishnakumar, Aravind Fernandes, Fernando Massa Bannister, Michele Bodewits, Dennis Dorsey, Rosemary La Forgia, Fiorangela Murphy, Brian Earth and Planetary Astrophysics Astrophysics of Galaxies We present high-resolution UVES+VLT observations of neutral nickel and iron atoms in the coma of the interstellar comet 3I/ATLAS taken after perihelion. Metal emission was strong shortly after perihelion and persisted at large heliocentric distances. At $r_h \sim 2$ au the total metal production rate was found to be at least an order of magnitude larger than that of typical solar-system comets. Post-perihelion production rates exhibit pronounced asymmetry compared to the pre-perihelion behavior: production rates are higher after perihelion and decline more gradually with $r_h$, the difference being stronger for FeI. The NiI/FeI abundance ratio, initially anomalously large before perihelion, evolved toward values comparable to solar-system comets near 2 au, and shows a weaker $r_h$ dependence after perihelion. To interpret these results, we revisited and extended the carbonyl hypothesis in which FeI and NiI are produced by the rapid photodissociation of Fe(CO)$_5$ and Ni(CO)$_4$ vaporized from the nucleus. Fits that include direct sublimation of carbonyls reproduce the observed rates and the high NiI/FeI line ratio, which is determined by the higher volatility of Ni(CO)$_4$. Desorption of carbonyls from sublimating CO$_2$ and H$_2$O ices is found to be negligible. The temperature profiles needed to reproduce the observations were found to be shallower than the equilibrium $T \propto r_h^{-1/2}$ relation, suggesting that the sublimation could occur below the surface of the nucleus. Fits using temperature profiles from thermal models require sublimation from depths of several cm, especially post-perihelion. An additional transient heat source ($T \simeq$ 100-140~K), possibly linked to the amorphous-crystalline ice transition, is proposed to explain the early NiI excess before perihelion. |
| title | Origin and evolution of NiI and FeI in the coma of the interstellar comet 3I/ATLAS throughout its trajectory |
| topic | Earth and Planetary Astrophysics Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2605.07652 |