X-SHOOTER Spectrum of Comet 3I/ATLAS: Insights into a Distant Interstellar Visitor

TL;DR

This study uses broad-wavelength spectroscopy to analyze the gas composition and physical environment of interstellar comet 3I/ATLAS, providing insights into its activity and surface properties.

Contribution

It presents the first optical and near-infrared spectrum of comet 3I/ATLAS, estimating upper limits on volatile production rates and characterizing its spectral slope.

Findings

Upper limits on OH and CN production rates

Spectral slopes consistent with D-type asteroids

Activity detected but volatile emissions below detection thresholds

Abstract

Comets are primitive remnants of the early Solar System whose composition offers fundamental clues to their formation and evolution. High-resolution, broad-wavelength spectroscopy is crucial for identifying volatile species and constraining the physical conditions within the coma. We aim to characterize the gas composition and physical environment of the newly discovered comet C/2025 N1 through optical and near-infrared spectroscopy. We used a medium-resolution spectrum of comet C/2025 N1 with X-shooter at the ESO Very Large Telescope (VLT), covering the 300-2500 nm wavelength range. Standard data reduction and flux calibration were applied. Although the object clearly shows activity, only upper limits to the production rates of OH and CN can be estimated: $8.0\times10^{24}$ s$^{-1}$ and $4.9\times10^{23}$ s$^{-1}$, respectively. We obtained red spectral slopes consistent with those of typical D-type asteroids and outer Solar System objects.