O₂ signature in thin and thick O₂−H₂O ices^⋆,⋆⋆

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
e-mail bmueller@mpe.mpg.de
² Ural Federal University, Ekaterinburg, Russia
³ Visiting Leading Researcher, Engineering Research Institute “Ventspils International Radio Astronomy Centre” of Ventspils University of Applied Sciences, Inženieru 101, Ventspils LV-3601, Latvia

Received: 1 June 2018
Accepted: 30 September 2018

Abstract

Aims. In this paper we investigate the detectability of the molecular oxygen in icy dust grain mantles towards astronomical objects.

Methods. We present a systematic set of experiments with O₂−H₂O ice mixtures designed to disentangle how the molecular ratio affects the O₂ signature in the mid- and near-infrared spectral regions. All the experiments were conducted in a closed-cycle helium cryostat coupled to a Fourier transform infrared spectrometer. The ice mixtures comprise varying thicknesses from 8 × 10⁻³ to 3 μm. The absorption spectra of the O₂−H₂O mixtures are also compared to the one of pure water. In addition, the possibility to detect the O₂ in icy bodies and in the interstellar medium is discussed.

Results. We are able to see the O₂ feature at 1551 cm⁻¹ even for the most diluted mixture of H₂O:O₂ = 9:1, comparable to a ratio of O₂/H₂O = 10% which has already been detected in situ in the coma of the comet 67P/Churyumov-Gerasimenko. We provide an estimate for the detection of O₂ with the future mission of the James Webb Space Telescope (JWST).