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

Abstract

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.

Martian Water Ice Clouds During the 2018 Global Dust Storm as Observed by the ACS‐MIR Channel Onboard the Trace Gas Orbiter

“…Every ACS‐MIR observation is composed of 20 spectral segments individually exhibiting broad instrumental shapes that generally prevent contiguous segments from matching precisely in their overlapping wavelength intervals (cf. Figure ) due to instrumental effects (Korablev et al, ; Trokhimovskiy et al, ). As the aerosol property derivation is intrinsically dependent of the continuum behavior, we have adopted a method to extract the continuum across all displayed fraction orders, taking into account this spectral shape of each order.…”

“…The ExoMars Trace Gas Orbiter (TGO), ESA‐Roscosmos Atmospheric Chemistry Suite (ACS), and Nadir and Occultation for MArs Discovery (NOMAD) instruments started their science operation phase in March 2018 (Korablev et al, , ; Vandaele et al, , ), before the MY 34 GDS. The ACS Mid‐InfraRed (MIR) channel is a crossed‐dispersion echelle spectrometer dedicated to solar occultation (hereafter, “SO”): each observation covers a 300‐nm wide spectral interval selected between 2.3 and 4.2 m. This interval is set by rotating the spectrometer secondary grating (i.e., the diffraction order separation) to align the interval of interest with the detector.…”

“…Thirteen different positions can be employed to completely sample the full accessible spectral range of the instrument. With the 2‐hr orbital period of TGO and the performing of SO in the mid‐infrared, ACS and NOMAD provide a totally new and huge data set of vertical profiles of the atmospheric extinction (Korablev et al, ; Vandaele et al, ). We are using the ACS‐MIR channel to study the extinction properties of the Martian airborne particles in the 3‐ m spectral region, which possesses a distinct diagnostic capability to identify the O‐H stretching signature, whether it is due to water ice absorption or bound water in dust.…”

Strong Variability of Martian Water Ice Clouds During Dust Storms Revealed From ExoMars Trace Gas Orbiter/NOMAD

“…The NOMAD (Vandaele et al, , ) instrument is onboard the ExoMars Trace Gas Orbiter 2016, an ESA/NASA mission to Mars. The spacecraft comprises also another multichannel spectrometer, the Atmospheric Chemistry Suite (ACS; Korablev et al, ). The main objective of NOMAD and ACS is to investigate Mars' atmosphere at unprecedented spectral resolution in the UV, Visible, and IR.…”

Hierarchical Modeling of Solar System Planets with Isca

“…There is a huge diversity of planetary atmospheres and data are sufficiently sparse (relative to that for Earth) that comprehensive modeling is difficult because of this lack of observational constraints. However, data are becoming available, both from Extra Large Telescopes on Earth, orbiting telescopes (Hubble and hopefully James Webb) (as reviewed in, e.g., [9], and references therein), and from missions to Solar System planets, such as the Exo-Mars Trace Gas Orbiter [77], Juno [78], and Dragonfly [79], the proposed exploration of Titan's atmosphere with a drone. Thus, quantitative comparison with data is becoming possible and therefore is, in conjunction with seeking a basic understanding, a goal of our modeling activities.…”