A search for methane in the atmosphere of Mars using ground-based mid infrared heterodyne spectroscopy

We report our search for methane in the atmosphere of Mars using high-spectral resolution heterodyne spectroscopy in the 7.8 μm wavelength region. Resolving power and frequency precision of >10 6 of the technique enable identification and full resolution of a targeted spectral line in the terrestrial-Mars spectrum observed from the ground. Observations were carried out on two occasions, in April 2010 and May 2012 at the McMath-Pierce Solar Telescope and the NASA Infrared Telescope Facility, respectively. A single line in the ν 4 band of methane at 1282.62448 cm −1 was targeted in both cases. No absorption due to methane was detected and only upper limits of ∼100 ppb for the martian atmospheric methane concentration were retrieved. Lack of observing time (due to weather) and telluric opacity greater than anticipated led to reduced signal-to-noise ratios (SNR). Based on current measurements and calculations, under proper viewing conditions, we estimate an achievable detection limit of ∼10 ppb using the infrared heterodyne technique – adequate for confirming reported detections of methane based on other techniques.