PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = "20/01/05" RECORD_TYPE = STREAM OBJECT = TARGET TARGET_NAME = "MARS" OBJECT = TARGET_INFORMATION PRIMARY_BODY_NAME = "MARS" ORBIT_DIRECTION = "PROGRADE" ROTATION_DIRECTION = "PROGRADE" TARGET_TYPE = "PLANET" TARGET_DESC = " Mars is one of two planets of the solar systems resembling the Earth much more than all others. Study of its atmosphere helps to understand better our own. There are evidences of earlier more dense atmosphere, warmer climate, open water on the surface, although it is not so simple to explain how warming was supported on the ancient Mars. The history of water on Mars is one of the most interesting problems in solar system studies. It is directly connected with possible presence of life on Mars at least in the long past. The investigation of Mars atmosphere performed so far has allowed to determine its average composition. It contains mainly carbon dioxide (95%), nitrogen (2.7%), and argon (1.6%) [Owen, 1992]. About ten of minor constituents were identified (section 2.5). The list of them includes water vapour playing important role in the atmospheric processes and surface/atmosphere interactions (section 2.6). Water vapour bands can be observed by PFS at both their channels, and observations of water vapour variations - time, latitudinal and place-to-place - is one of important task for the PFS. Simultaneous observations in SW and LW bands will provide estimates of atmospheric H2O vertical distribution. Global annual average surface temperature of Mars is 210 K [2]. The atmosphere of Mars is colder than terrestrial on all heights (Figure 1). In general the vertical structure of both can be divided on three main regions: low atmosphere, middle atmosphere (mesosphere) and upper atmosphere (thermosphere). The middle atmosphere of Mars is its coldest part. Here is the sink for the energy flux coming from the surface and troposphere (heated by Solar visible and near IR radiation) and also from the thermosphere. There are a few important qualitative differences with terrestrial atmosphere: 1) no temperature maximum inside of the middle atmosphere, 2) lapse rate in the low atmosphere, 3) strong daily variations near the surface due much lower thermal capacity, 4) strong influence of the aerosols on the atmospheric heating. Horizontal differences in temperatures lead to differences in pressure, but they are smoothed by winds. Winds transfer heat together with air masses. This influence local temperature profiles. Also the dust can be lifted from the surface and temperatures are changed by this also. Condensation is another way of formation of aerosols, also with a feedback on temperatures. Winds depends from topography. So the realistic computation of GCM (General Circulation Models) taking in account all of these effects is very difficult task. However there are a few groups of theoreticians that reached a large progress in such sort of modelling. What they have now are mainly data of IRIS Mariner-9 for 2 seasonal latitudes Ls 43-540 and 3740 (full profiles) and much less informative Viking IRTM atmospheric temperatures. Using PFS observations of the Martian 15 microns band (by its LW- channel) we intend to fill this gap. Such measurements will strengthen the empirical base for the check of GCM for Mars. Aerosols play a great role in the formation and variations of 3-D temperature and winds pattern in the atmosphere of Mars. There are two sorts of aerosols there: lifted from surface dust and condensates. The event of GDS (Global Dust Storms) is the most pronounced appearance of dust influence on the Martian meteorology but in reality aerosols are always present in the atmosphere and both kinds participate in heating/cooling processes. Chemical nature (minerals/ices), size distribution, optical depth of aerosols medium will be estimated from PFS observations. Simultaneous use of SW and LW channels should be very helpful. Table 2.1 Most important atmospheric spectral features in the spectrum of Mars. ----------------|-----------|-------------|------------------------- | | | Wavelength, | Nature | Intensity | Results to m | | in the Mars | be obtained | | spectrum | from observations ----------------|-----------|-------------|------------------------- 1.38 | H2O | weak | H2O column abundance ----------------|-----------|-------------|------------------------- 1.43, 1.54, | CO2 | middle | surface pressure 1.61, 1.65 | | | ----------------|-----------|-------------|------------------------- 1.6 | H2O ice | * | ice particles, tau and | | | sizes ----------------|-----------|-------------|------------------------- 1.87 | H2O | weak | H2O column abundance ----------------|-----------|-------------|------------------------- 1.96, 2.01, | CO2 | strong | surface pressure 2.05 | | | ----------------|-----------|-------------|------------------------- 2.35 | CO | weak | CO column abundance ----------------|-----------|-------------|------------------------- 2.7 | H2O | middle | H2O column abundance ----------------|-----------|-------------|------------------------- 2.69, 2.77 | CO2 | strong | surface pressure ----------------|-----------|-------------|------------------------- 3.7 | HDO | weak | D/H(?) ----------------|-----------|-------------|------------------------- 4.25 | CO2 | strong | # ----------------|-----------|-------------|------------------------- 6.3 | H2O | middle | ## ----------------|-----------|-------------|------------------------- 9 | SiO2 dust | * | mineral composition, tau | | | and sizes ----------------|-----------|-------------|------------------------- 11 | H2Oice | * | ----------------|-----------|-------------|------------------------- 15.0 | CO2 | strong | temperature profile ----------------|-----------|-------------|------------------------- 30-45 | H2O | middle | H2O column abundance ----------------|-----------|-------------|------------------------- Rem.: * depends of optical depth of aerosols # this bands are near boundary between regions of reflected and thermal radiation and the possibility to use it is doubtful. ##this band is not available for PFS because is on the boundary of its LW range. Previous data evidenced both seasonal and daily variations and occasional climatic events. During the northern winter-time two different regimes have been observed, in various years: in the first case one or more dust storms cover nearly all the - planet; in the second regime no global storm occurs but high winds produce dust raise in confined regions. On the contrary, summer weather appears - more repetitive as winds are generally low and evolve on a diurnal time - scale. Storms are very peculiar events which require a more detailed - investigation. Pressure profiles, wind patterns and atmospheric dust - evolution must be carefully analysed to determine the effects produced on the surface morphology, too. In fact, surface feature changes produced by atmospheric activity have been revealed by means of albedo pattern - observations and suggest a close coupling of surface morphology with - ambient evolution. In particular, chemical and physical processes at the boundary between lithosphere and atmosphere have to be better described and understood. The temperature changes control the polar cap condensation rate and influence the formation and the evolution of clouds. Until now, white condensation (mainly water ice) clouds have been observed; however, their evolution and detailed composition are still uncertain. Atmospheric data can be also relevant, in combination with surface composition analyses, to determine: a) distribution, abundance, physical status of water on the planet; b) volatile distribution and abundance in the atmosphere, on the crust, and at depth; c) outgassing processes . In conclusion we will summarise (Table 2.1) the most important 'prints' left by the atmosphere of Mars into the spectrum of the planetary radiation within the PFS spectral range (1.2 - 45 microns). The spectrum of Mars (as for any planet ) consist of two part: short wavelengths dominated by bireflected solar radiation and long wavelengths dominating by the thermal radiation of planet. In the case of Mars the boundary of this two region is near 4 microns. SW and LW ranges of the PFS instrument practically correspond to these two parts of the Martian spectrum. Bands of atmospheric gases in short wavelengths range appears only as absorption features, in long wavelengths they can appear as absorption (if atmospheric temperature goes down with height) or emission (if it goes up), occasionally the band may have a complicate shape." END_OBJECT = TARGET_INFORMATION END_OBJECT = TARGET END