REMS has been designed to measure ambient humidity, pressure, wind speed and direction, air and ground temperature and UV radiation [Gómez-Elvira, 2008]. With REMS, MSL will have the opportunity to make environmental measurements in an extensive area during its nominal one Mars-year long mission. Thus, REMS will detect daily and seasonal variations. At the same time, REMS will collect data at different locations and, as a consequence, different Martian environments. REMS will achieve its science goals using simple sensors with flight heritage.

The REMS surface humidity measurements will complement those made by orbiters. At the same time, such a measurement will help to constrain the seasonal flux of moisture into and from the regolith, which cannot be measured well from orbiters. Measurements of surface pressure, temperature and wind will improve our understanding of the dynamics of the MBL by quantifying turbulence, gravity-inertia waves, and surface (rocks, minerals and regolith)/atmosphere interactions. Specifically, in the case of theGTS (Ground Temperature Sensor), further information about surface composition (including water) is also achieved. Pressure data will yield information on the global dust abundance and atmospheric motions on scales from the global tide to the passage of dust devils. Temperature and wind data will yield more direct information about Mesoscale motions and turbulence in the MBL. These measurements may shed some light on the generation of regional dust storms. Strong winds pick up the dust and transport it around the planet. Whenever the winds[Dominguez, 2008],[Kovalski, 2009] are strong enough to move dust, the rover cameras might detect changes in the surface features. These data can be used to determine the critical frictional velocity for saltation, and, therefore, shed light of the most important geological process actively shaping the Martian surface. UV measurements will provide information about relevant aspects related to the chemical-mineralogical setting and possible biology of the MBL4-8. Ionizing UV radiation is a damaging agent for life, especially on planetary bodies where no protective atmospheres are present. For this reason, the knowledge of the UV opacity [Vazquez, 2007] and, in general, intensity and spectrum of UV radiation at the surface of Mars has important implications for habitability. This is the first time that UV flux will be measured at the Martian surface. Data analysis will be based on comparison with data from Earth in the range 200-400 nm divided into seven bands. The UVC region (200-280 nm) is the most relevant from the biological point of view and will shed light on the possible shielding mechanism of suspended aerosols such as the dust.

In the general context of science, REMS investigations will range from surface-atmosphere interactions and boundary layer phenomena into large-scale atmospheric flows and global circulation. Basically, the REMS science investigation focuses on five scientific areas according to the following five scientific goals:

1.Microscale Dynamics: Characterization of the near-surface meteorological environment.

It is related to the near-surface meteorological environment which contains Microscale or MBL processes of free or forced convection (~10 m-10 km). A key issue will be to relate the properties of the near-surface meteorological environment to the nature of the physical processes causing surface-atmosphere interaction.

The following objectives are considered in the context of the MBL: a) information on surface-layer turbulence structure and mean vertical gradients; b) to detect and observe convective vortices; c) CO2 cycle. To compare the seasonal pressure variations with those of Viking and Pathfinder; d) threshold for dust lifting. Wind records, and d) effects of changes of the local environment (topography, albedo) in the local meteorology.

2. Mesoscale Dynamics.

It includes flows forced by interaction of solar heating and large-scale winds with topography or other surface inhomogeneity (10-1000 km). Intense mesoscale circulations are expected to occur primarily in association with topographic features or sharp contrast in surface thermal properties. They also can be associated with low-pressure weather systems, which may be observable if MSL lands at the high-latitude edge of its planned operating range. Larger topographic and thermal contrasts are expected to generate migrating air masses with associated mesoscale fronts. The REMS objective is to detect Mesoscale Fronts through: 1) diurnal cycle of wind, and 2) sharp temperature changes.

3. Synoptic Meteorology and the Influence of Dust.

Time-series of in situ measurements will provide unique information about the local environment, and about the global atmosphere. Three major types of large-scale systems can potentially be studied with REMS: thermal tides, mean large-scale circulations, and low pressure weather systems and extra-tropical waves (if at a sufficiently high latitude).

The thermal tides are in many ways the most important. The specific objectives are: a) studies of Atmospheric Global Waves; b) analysis of the slow components of the pressure variations; c) detection of dust storms away from the lander via the thermo tidal signature in the surface pressure diurnal cycle, and d) Martian climate and circulation regimes: studies of the similarities and differences between Viking and MSL observational periods.

4. The Local Water Cycle.

Water is a major focus of the Mars Exploration Program because it is essential to sustain life as we know it. Mars exhibits an active water cycle, involving water transport between the poles and exchange of water between the atmosphere and the surface/subsurface, where it can be adsorbed or freeze. The in situ abundance of water vapor at the Martian surface has never before been measured. The main scientific goals of REMS are the following: 1) to find the most important physical/chemical processes that control the exchange of water vapor between the surface and the atmosphere; 2) to determine the spatial and temporal fluctuations of water vapor at the surface on diurnal and seasonal time-scales; 3) to understand the consistency of diffusive transport of water vapor in and out of the regolith (including different types of water-related substrates and different mineralogical mixtures) [Martin-Redondo, 2009] with the presence of large reservoirs of near surface ice; 4) to ascertain if the global water cycle is closed on annual basis.

5. Quantification of the local UV radiation environment.

The evaluation of the local UV radiation environment in order to asses its role in chemical and biological processes. To know the surface UV environment is of critical importance for life because UV photons do ionize biogenic chemicals. Correlations between UV (UVA, UVB and UVC) radiation doses with temperature and pressure would provide a better understanding of the role of UV radiation on the MBL. The main objectives are the following: a) interaction of UV Radiation, and b) UV shielding related with Martian rocks and minerals.

Mars Atmosphere

In many ways the climate of Mars resembles that of the Earth, particularly in its daily cycle and yearly sequence of seasons. These affinities result from the many coincidences in the celestial motions of the two planets: the Martial day, or sol, is 24h40m long; Mars completes an orbit around the Sun in approximately 2 earth years; its axis of rotation is tilted with respect to the orbital plane only slightly more than the Earth’s (25.2 deg. and 23. deg. respectively). However, the eccentricity of the Martian orbit is much higher and at a mean distance from the Sun of 1.5 AU, over one complete orbit Mars receives only about half as much sunlight as the Earth. As a consequence, and also because there are no oceans on Mars, the Martian surface is colder and experiences greater seasonal temperature changes and more pronounced diurnal variations, with differences between the night minimum and afternoon maximum of 70 degrees or more.[more]