Capillary Absorption Spectrometer (CAS), a compact, low-sample-volume isotope analyzer for planetary applications

Isotope-ratio analysis is a powerful tool to elucidate planetary systems. Isotopic data can provide information on potential sources of water in the solar system (e.g., D/H ratio), as well as evidence for life beyond Earth (e.g., 13C/12C and 34S/32S). We describe a trace-gas and isotope analyzer that utilizes a low-volume (~1 ml), compact gas cell, in a concept we refer to as a Capillary Absorption Spectrometer (CAS). An analyte is drawn into a hollow fiber, which has a reflective inner coating that guides a tunable laser beam to a detector. There is near unity overlap between the laser beam and the gas sample in the fiber, leading to a highly sensitive system with an ultra-compact size. The measurement approach is similar to the Tunable Laser Spectrometer (TLS) aboard the Curiosity Rover, with the difference being that the CAS can perform measurements with orders of magnitude less sample. The CAS on missions to the Moon will help better understand Lunar water sources, or the CAS on an Enceladus plume fly through can provide insight into methane origins. With the CAS low SWaP, it is an appealing instrument for numerous missions to help answer pivotal questions.