Possible influence the composition of martian surface on visibility the spectral features of atmospheric trace gases in mid-infrared spectra - The results of simulations

Abstract

The paper focuses on influence the optical features of minerals of the surface of Mars on remotely detected gaseous components of the Martian atmosphere, when the spectrometer receives a combined signal from the Martian soil and atmosphere. Our considerations concern above all the detectability of methane, but the problem may also apply to other trace gases.Possible detections of methane in the atmosphere of Mars has been reported from the Mars Express (orbiting Mars), Curiosity on the surface of Mars and from Earth and its presence in the Martian atmosphere is being questioned again today. The reason for these doubts is that the excellent NOMAD spectrometer the part of payload of ExoMars Trace Gas Orbiter has repeatedly detected only extremely low amounts of methane in the atmosphere above 5 km, using very sensitive solar occultation method. So far there is no new information about the content of methane in the lower layers of the atmosphere. However, assuming its presence in this part of the atmosphere due to its possible source in the ground, as suggested by some works, it may be considered whether the spectral characteristics of the soil may hinder remote detection of methane. One of the discussed examples refers to possible observation of methane over mineralogical surfaces which may be the source of this gas. The examples of other mineralogical compositions of the surface were also taken into account. The series of numerical simulations carried out in the region of a strong methane absorption band and the examples in which the optical characteristics of the surface change the shape and contrast of the absorption band of methane are shown.The used codes provide estimates of the spectral reflectance/emittance and the total radiance of the Martian surface and atmosphere in the Mid-Infrared spectral range. The surface covered with dust were described by the reflectance and emittance, calculated from n,k with Mie and Hapke theories or known from laboratory measurements were used. The various concentrations of atmospheric gases were taken into account.In the future, we intend to enrich our reflectance and emissivity examples with the cases provided by the Cassis camera the part of payload of ExoMars Trace Gas Orbiter (TGO) of the ESA mission in which researchers from SRC – PAS are engaged. The Cassis camera can give us the opportunity of analysis the real structure, colour and locations on the surface of Mars possible sources of trace gases e.g. methane. Identification and monitoring the minor species in the atmosphere are performed from orbiter by spectrometric instruments (e.g. NOMAD, ACS).