Reader response draft 3.0

 The article “NOMAD, an Integrated Suite of Three Spectrometers for the ExoMars Trace Gas Mission: Technical Description, Science Objectives and Expected Performance”, discusses a spectrometer suite incorporated into the ExoMars Trace Gas Orbiter, NOMAD (“Nadir and Occultation for Martian Discovery”).NOMAD comprises of three spectrometers: Solar Occultation (SO), Limb and Nadir Occultation (LNO) and Ultraviolet/Visible Spectrometer (UVIS). The SO spectrometer only performs solar occultation and works in the infrared range(2.3-4.3um). The LNO spectrometer is capable of performing solar and nadir occultation and limb observations and also operates in the infrared range(2.3-3.8um. The UVIS spectrometer operates in the ultraviolet and visible light range(200-650nm) and can be used to detect carbon dioxide ice grains at high altitudes. These spectrometers work with each other to collect data which allows us to understand Mars’ “atmospheric composition and the related physical and chemical processes”(Vandaele et al., 2017).

NOMAD is the only instrument which is highly sensitive that can provide vertical profiles and map trace gases, main constituents, temperature and dust/clouds present on Mars’ atmosphere.

NOMAD uses three spectrometers in conjunction with each other to detect gases like carbon dioxide (CO₂), nitrogen dioxide(NO₂), water vapour(H₂O) and hydroperoxyl(HO₂). The high resolution of the SO and LNO spectrometer allows for a greater sensitivity when detecting the trace gases and its different isotopes. The table 2: The LNO and UVIS detection limits for nadir and solar occultation geometry from the article “NOMAD, an Integrated Suite of Three Spectrometers for the ExoMars Trace Gas Mission: Technical Description, Science Objectives and Expected Performance” provides evidence for this.

Hydroperoxyl compound has never been measured before and NOMAD has been able to detect it during the solar occultation mode. This proves that NOMAD is an extremely sensitive instrument that is capable of detecting gases even ones that have never been discovered before.

Creating vertical profiles of these gases are extremely important as they provide a graphical representation of the data collected and it is easier to interpret the data collected. As stated by Vandaele et al, NOMAD is the only instrument that can produce a “high vertical resolution of the key species (H2O, O3, HO2,...)” using its three spectrometers.

The only thing NOMAD wasn’t able to detect is the Methane gases which has been one of the few gases that is widely searched for in Mars by every rover sent to Mars. This is because presence of methane signifies the possibility of life on Mars. NOMAD was unable to detect any trace of methane in Mars’ atmosphere despite the fact that NASA’s Curiosity rover had just detected the “highest burst of methane recorded yet”. The European Space Agency has stated in their article “ESA’s Mars orbiters did not see latest Curiosity methane burst” (ESA,2019) that the measurements taken varies according to how dusty the environment is and this could have contributed to the lack of methane detection.

It can be concluded that NOMAD is a highly sensitive instrument capable of measuring various gases including detecting the presence of new gases such as hydroperoxyl and the lack of methane detection is probably due to the dusty Mars’ atmosphere. NOMAD is one of the best suited instruments to detect gases and provide vertical profiles of these gases.

References

         

European Space Agency (2019, November 13) ESA's Mars Orbiters did not see latest curiosity methane burst. Retrieved October 10, 2021, from https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Exploration/ExoMars/ESA_s_Mars_orbiters_did_not_see_latest_Curiosity_methane_burst.

Vandaele, A. C., Lopez-Moreno, J.-J., Patel, M. R., Bellucci, G., Daerden, F., Ristic, B., Robert, S., Thomas, I. R., Wilquet, V., Allen, M., Alonso-Rodrigo, G., Altieri, F., Aoki, S., Bolsée, D., Clancy, T., Cloutis, E., Depiesse, C., Drummond, R., Fedorova, A., … Wolff, M. (2018). Nomad, an integrated suite of three spectrometers for the ExoMars Trace Gas Mission: Technical Description, science objectives and expected performance. Space Science Reviews, 214(5). https://doi.org/10.1007/s11214-018-0517-2

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