A sensitive search for organics (CH4, CH3OH, H2CO, C2H6, C2H2, C2H4), hydroperoxyl (HO2), nitrogen compounds (N2O, NH3, HCN) and chlorine species (HCl, CH3Cl) on Mars using ground-based high-resolution infrared spectroscopy

Is Mars actively releasing organic and other minor gases into the atmosphere? We present a comprehensive search for trace species on Mars, targeting multiple volatile organic species (CH4, CH3OH, H2CO, C2H6, C2H2, C2H4), hydroperoxyl (HO2), several nitrogen compounds (N2O, NH3, HCN), and two chlorine species (HCl, CH3Cl) through their rovibrational spectra in the 2.8–3.7 μm spectral region. The data were acquired over a period of 4 years (2006–2010) using powerful infrared high-resolution spectrometers (CRIRES, NIRSPEC, CSHELL) at high-altitude observatories (VLT, Keck-2, NASA-IRTF), and span a broad range of seasons, Doppler shifts and spatial coverage. Here, we present results from a selection of high-quality spectra obtained on four separate dates, representing a fraction of our search space. For most of these species we derived the most stringent upper limits ever obtained, and because the targeted gases have substantially different resident lifetimes in the Martian atmosphere (from hours to centuries), our measurements not only test for current release but also provide stringent limits on the quiescent levels. In particular, we sampled the same regions where plumes of methane have been recently observed (e.g., Syrtis Major and Valles Marineris), allowing us to test for seasonal and temporal variability.