Spectral mapping of Mars and Venus : searching for their past and present histories

Over the past decades, high-resolution spectroscopy has led to the identification of minor planetary atmospheric species with mixing ratios as low as a few parts per billion (ppbv). More recently, the advent of bi-dimensional infrared arrays has allowed us to map the distribution of these components over planetary disks, and to use them as tracers of dynamical and photochemical processes. In complement to in-orbit observations recorded by space missions, high-resolution spectral mapping from the ground allows us to obtain instantaneous global maps of the planets, and thus to trace transient phenomena or temporal variations of minor atmospheric species over short and long timescales. Over the past twenty years, we have been monitoring the behavior of minor atmospheric species on Mars and Venus, using the TEXES (Texas Echelon Cross Echelle Spectrograph) at the NASA IRTF (InfraRed Telescope Facility) at Maunakea Observatory, and the EXES (Echelon Cross Echelle Spectrograph) aboard SOFIA (Stratospheric Observatory For Infrared Astronomy): H2O2 and H2O on Mars, D/H on Mars, SO2 and H2O at the cloud top of Venus. In addition, in an attempt to build a 3-D image of the sulfur and water cycles on Venus, we have obtained maps of SO, SO2 and HDO in its upper mesosphere (about 20 km above the cloud top) using the ALMA (Atacama Large Millimeter/submillimeter Array) facility in Chile. All these observations will be presented and discussed in the light of global dynamical and photochemical models, and interpreted in the context of the past and present history of these planets .