Response of dust on thermal emission spectra observed by Planetary Fourier3 Spectrometer (PFS) on-board Mars Express (MEX)

The thermal emission spectra have provided many useful insights about the Martian atmosphere and surface. The interpretation of the thermal emission spectra can give us information about atmospheric temperature, pressure, mineralogy and presence of atmospheric constituents including their isotopes. In the present work, we have analysed the thermal emission data for dust storm season on Mars. The signature of dust in the thermal emission spectra for Martian Year (MY) 28 confirms presence (Ls=280 o and 300 o ) and absence (Ls=240 o and 320 o ) of the dust storm at latitude range 0 o -10 o S, 10 o -20 o S and 20 o -30 o S. We have compared our results with earlier mission data with thermal emission measurements made by Planetary Fourier Spectrometer (PFS) on-board Mars Express (MEX) between wave numbers 250-1400 cm -1 . We have observed features at wave numbers 600-750 cm -1 and 900-1200 cm-1 due to absorptions by CO 2 and dust respectively. We have obtained brightness temperatures from thermal emission spectra by inverting the Planck function. The maximum brightness temperature ~280 K is measured at Ls=240 o when Mars received a large amount of solar radiation at perihelion. The minimum brightness temperature ~ 220 o K is observed at Ls=320 o in the absence of dust storm. In presence of dust storm thermal emission spectra and brightness  temperatures are reduced by factors of ~ 3.0 and ~1.3 respectively between wave numbers 900-1200 cm -1 in comparison to that observed in absence of dust storm.