The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter

The Atmospheric Chemistry Suite (ACS) package is an element of the Russian contribution to the ESA-Roscosmos ExoMars 2016 Trace Gas Orbiter (TGO) mission. ACS consists of three separate infrared spectrometers, sharing common mechanical, electrical, and thermal interfaces. This ensemble of spectrometers has been designed and developed in response to the Trace Gas Orbiter mission objectives that specifically address the requirement of high sensitivity instruments to enable the unambiguous detection of trace gases of potential geophysical or biological interest. For this reason, ACS embarks a set of instruments achieving simultaneously very high accuracy (ppt level), very high resolving power (>10,000) and large spectral coverage (0.7 to 17 μm—the visible to thermal infrared range). The near-infrared (NIR) channel is a versatile spectrometer covering the 0.7–1.6 μm spectral range with a resolving power of ∼20,000. NIR employs the combination of an echelle grating with an AOTF (Acousto-Optical Tunable Filter) as diffraction order selector. This channel will be mainly operated in solar occultation and nadir, and can also perform limb observations. The scientific goals of NIR are the measurements of water vapor, aerosols, and dayside or night side airglows. The mid-infrared (MIR) channel is a cross-dispersion echelle instrument dedicated to solar occultation measurements in the 2.2–4.4 μm range. MIR achieves a resolving power of >50,000. It has been designed to accomplish the most sensitive measurements ever of the trace gases present in the Martian atmosphere. The thermal-infrared channel (TIRVIM) is a 2-inch double pendulum Fourier-transform spectrometer encompassing the spectral range of 1.7–17 μm with apodized resolution varying from 0.2 to 1.3 cm−1. TIRVIM is primarily dedicated to profiling temperature from the surface up to ∼60 km and to monitor aerosol abundance in nadir. TIRVIM also has a limb and solar occultation capability. The technical concept of the instrument, its accommodation on the spacecraft, the optical designs as well as some of the calibrations, and the expected performances for its three channels are described

Investigations of the Mars Upper Atmosphere with ExoMars Trace Gas Orbiter

The Martian mesosphere and thermosphere, the region above about 60 km, is not the primary target of the ExoMars 2016 mission but its Trace Gas Orbiter (TGO) can explore it and address many interesting issues, either in-situ during the aerobraking period or remotely during the regular mission. In the aerobraking phase TGO peeks into thermospheric densities and temperatures, in a broad range of latitudes and during a long continuous period. TGO carries two instruments designed for the detection of trace species, NOMAD and ACS, which will use the solar occultation technique. Their regular sounding at the terminator up to very high altitudes in many different molecular bands will represent the first time that an extensive and precise dataset of densities and hopefully temperatures are obtained at those altitudes and local times on Mars. But there are additional capabilities in TGO for studying the upper atmosphere of Mars, and we review them briefly. Our simulations suggest that airglow emissions from the UV to the IR might be observed outside the terminator. If eventually confirmed from orbit, they would supply new information about atmospheric dynamics and variability. However, their optimal exploitation requires a special spacecraft pointing, currently not considered in the regular operations but feasible in our opinion. We discuss the synergy between the TGO instruments, specially the wide spectral range achieved by combining them. We also encourage coordinated operations with other Mars-observing missions capable of supplying simultaneous measurements of its upper atmosphere

Long-term O2 nightglow observations in the polar night on Mars by SPICAM/MEx

International audienceWe will present preliminary results of the O nightglow observations in Northern and Southern hemispheres at different Martian years

Exploration of Mars in the SPICAM-IR experiment onboard the Mars-Express spacecraft: 2. Nadir observations: Simultaneous observations of water vapor and O2 glow in the Martian atmosphere

The SPICAM experiment onboard the Mars-Express spacecraft includes sounding the Martian atmosphere in the ultra-violet (118–320 nm) and near IR (1–1.7 ?m) ranges. The infrared spectrometer operates in the range of 1–1.7 ?m with a resolution of 3.5 cm?1 in the mode of nadir observations and solar and stellar occulations. This paper is devoted to analyzing the basic results of nadir observations of the infra-red SPICAM channel during the first Martian year of the instrument operation: from January 2004 to November 2005. One of the primary goals of SPICAM-IR is water vapor monitoring in the atmosphere of Mars in the band of 1.37 ?m and ozone abundance determination from the day-time airglow of molecular oxygen O2(a 1?g) in the band of 1.27 ?m. Simultaneous measurements of these minor constituents of the planet are necessary for understanding photochemical processes in the Martian atmosphere. The degree of their anticorrelation and a comparison with the results of photochemical modeling of the atmosphere will contribute to our knowledge of the Martian atmosphere stability

Seasonal Variation of Aerosol Vertical Distribution in the Martian Atmosphere and Detection of the Bimodal Distribution from Solar Occultations on Mars-Express

International audienceDust cycle is one of the most important in the Martian climate system. Martian dust, consisting mainly of mineral particles, lifts from the surface by winds and dust devils. Being active radiation, dust with water clouds is involved in the heating and cooling of different atmospheric layers, absorbing, scattering and re-radiating solar radiation in the thermal infrared. Furthermore, the dust particles are condensation nuclei for the formation of water and CO2 ice clouds.We will present results of long-term observations of the Martian atmosphere by solar occultation technics in the near-IR range. SPICAM spectrometer on board the Mars Express spacecraft has been working on the orbit of Mars since January 2004. During the four Martian years 800 solar occultations have been performed. SPICAM spectral range allows simultaneous observations of 1.43 μm CO2 band for the atmospheric density, the 1.38 μm absorption band of water vapor to get the H2O density, and the distribution of aerosols with altitude measuring the opacity of the atmosphere in the spectral range from 1 to 1.7 μm. In the experiment, aerosol extinction profiles have been obtained at altitudes from 0 to 90 km with a vertical resolution of 2 to 10 km depending on distance to limb. We also consider their seasonal and latitudinal variations. Retrieved values of effective radius vary from 0.1 to 1.5 μm.Special attention was paid to the summer in the northern hemisphere, where the water vapor supersaturation in the middle atmosphere has been recently discovered (up to the values of S = p/psat ~ 3–5) [1]. Simultaneous analysis of aerosol extinction in the UV and IR range at different altitudes during this period has enabled the first direct detection of a bimodal distribution of Martian dust particles with characteristic radius of 0.04–0.07 μm and 0.7–0.8 μm. The number density of small fraction varies from 103 cm-3 at 10 km to 10cm-3 at 40 km. The concentrations and the effective radius of the particles correspond to the Aitken particles in the Earth's atmosphere. Unfortunately, the spectrometer cannot determine the nature of the particles, so dust and ice particles were considered. Such concentration of small particles in the presence of a large fraction should be unstable to coagulation process, The coagulation time for obtained bimodal di stribution varies from 1 to 50 days, which requires a source of particles. If it is not the condensation phase, the particles lift from the surface. The sedimentation time varies from 100 to 1000 days (for particles 0.1 microns and 0.01 microns, respectively) at 20 km and 10 to 100 days at 40 km, and these particles may be transported by Hadley cell from the northern to the southern hemisphere in the observed period of the summer solstice in the northern hemisphere