AGO

Séminaires du
Département d'Astrophysique, Géophysique et Océanographie

http://www.ago.ulg.ac.be/PeM/Semi

Jeudi 22 octobre, 16h00

Salle de réunion AGO (local -1/14)
Institut d'Astrophysique et de Géophysique
Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

From Quiescence to Glow: Unveiling the Pre-Perihelion Activity of Interstellar Comet 3I/ATLAS through Multi-Epoch Spectroscopy

Rohan Rahatgaonkar
(Pontificia Universidad Católica de Chile)



The discovery of 3I/ATLAS (C/2025 N1) in July 2025 marked the detection of the third confirmed interstellar object passing through our Solar System, and the first ISO discovered several months before perihelion. With an extreme hyperbolic orbit (e ≈ 6.14) and an estimated age older than the Solar System, 3I/ATLAS provides a unique window into the chemistry and conditions of ancient extrasolar planetary systems. We present spectroscopic observations from SOAR and VLT facilities tracking 3I from 4.4 to 2.85 AU, revealing its evolution from quiescence to activity. Our data show a red continuum spectrum with complex organics, the dramatic onset of CN emission at 3.65 AU, and remarkably, strong Ni I emission beginning at 3.78 AU with no detectable Fe I. The unusually steep heliocentric scaling of production rates (Q(Ni) ∝ r_h^(-7.7) and Q(CN) ∝ r_h^(-6.7)) suggests low-activation-energy release mechanisms inconsistent with simple volatile sublimation, potentially involving metal carbonyls or metalated organics. I will discuss these findings in the context of 3I's ancient origins and our campaigns to monitor its evolution through pre-perihelion.