P51B-1407
Real Solar Irradiance Data for Planetary Surface Studies
The precise determination of the solar irradiance (or extraterrestrial spectrum - ETS) is of primary importance for converting space-borne remote sensing radiance data to accurate reflectance values necessary for geological interpretations of planetary surfaces. Historically, the ETS has been determined from either calculating an emitted spectrum based on the Sun's composition, or modeling and removing atmospheric interferences on a solar spectrum obtained by telescopic observations, aircraft, and/or ground measurements. However, modeling an atmosphere is incredibly complex. A solar spectrum thus measured is replete with absorptions caused by molecular vibrations of atmospheric gases and scattering by particulates at wavelengths that would otherwise be diagnostic of petrological or atmospherical properties. An ETS calculated from these measurements must make some general assumptions about atmospheric conditions at the time of acquisition in order to compensate for their effects. However, variations in local pressures, humidity, and particulate compositions present a many-bodied problem that preclude a truly accurate model. Nevertheless, these model spectra are the basis for the ETS used for atmospheric and planetary surface studies. The Spectral Irradiance Monitor (SIM) onboard the Solar Radiation and Climate Experiment (SORCE) provides a better alternative to theoretically-derived ETS by directly measuring the solar irradiance, outside the Earth's atmosphere. For almost six years, SIM has been taking daily measurements of the ETS at wavelengths between 200 and 2400 nm. This spectral range covers most absorption bands diagnostic of mafic mineralogy, thus making SIM's data ideal for terrestrial planetary mapping. Furthermore, SIM's daily measurements allow for enhanced meteorologic studies of other planetary atmospheres. SIM's spectral resolution and signal to noise ratio meet or exceed the sensitivity of current spectrometer detectors.
P51B-1408
Martian Ionospheric Loss Rates: Now and Then
Over the course of the last few years a variety of research groups have been engaged in simulating the loss of Mars' ionosphere by solar wind interactions with the Martian ionosphere. The research being reported in this paper was performed by using 3-D hybrid particle simulations with a dynamic set of chemistry equations representative of the chemistry that forms and maintains the Martian ionosphere. The paper to be delivered at this meeting addresses scaling of these pickup rates as a function of several variables. These variables EUV flux, neutral density profiles and solar wind parameters are known to be substantially different in earlier epochs of the Martian existance. Knowledge of how the loss rate varies with these parameters will provide researchers with a better understanding of the atmospheric evolution of the planet as well as a possible understanding what happened to some of the water that existed on Mars at earlier times.
P51B-1409
Origin of MGS-Observed Electron Flux Enhancements Using 3D Multi-Fluid Simulations of the Martian Solar Wind Interaction
Previously we reported a discovery of a seasonal, nighttime clustering of particle enhancements on the Mars Global Surveyor electron flux data at low-energy levels observed over a localized geographical region in the southern hemisphere of Mars. This enhancement is likely the result of the transport of photoelectrons produced above the crustal magnetic sources on the dayside of Mars, to the magnetotail on the nightside of Mars. The transport would occur along the lines of the reconnected Interplanetary Magnetic Field (IMF). In this study, we explore the origin of the observed electron flux enhancements using three-dimensional multi- fluid simulations of the Martian solar wind interaction. Using the model, the magnetic field configuration and plasma distribution around Mars is reproduced for typical solar wind conditions and crustal field orientations. The results are compared to the observations, and consequently the possible role of magnetic reconnection between the draping IMF and the crustal fields in the observed electron enhancements is discussed.
P51B-1410
Seasonal Variation of Oxygen in the Upper Atmosphere of Mars
We have inferred the abundance of O2 in the upper atmosphere of Mars using observations of stellar occultations by the SPICAM UV spectrograph on Mars Express. The distribution of O2 with altitude, latitude, and season is an important factor in the evolution and current stability of Mars's CO2-rich atmosphere. Interpreting the occultation data depends only on the ratio of attenuated to unattenuated spectra, so relative measurements yield absolute abundances. O2 is detected in the presence of the much more abundant CO2 by its absorption in the Schumann-Runge bands and continuum, which lie in the wavelength range 130--205~nm. A vertical inversion algorithm converts the column abundances measured directly in the occultation to volume abundances. We have concentrated on the Southern hemisphere during its winter season, when we expect that O2 will be easier to detect owing to the lower CO2 abundance. The measurements reveal the altitude profiles of O2 in the altitude range of ~70--120~km. The probable error is about 10--20% for most of this range, but uncertainties in the O2 absorption cross-sections at the relevant wavelengths lead to larger probable errors in O2 abundance over a range of about 15~km. We infer the altitude profiles of CO2 over the full altitude range from the same measurements, with much lower uncertainty. The 190 occultations analyzed to date cover discrete latitudes from 16S to 75S and span the range 90° < LS < 190°. We report results in terms of the mixing ratio of O2 relative to CO2 by number. The most reliable determinations of this value are in the altitude range ~100--120~km, but results at other altitudes are qualitatively similar. The ratio [O2]/[CO2] varies with season and latitude, from ~0.001 to ~ 0.03. The lower values are similar to the commonly-used value of 0.0012, but our new measurements show that often much higher values obtain.
P51B-1411
Thermal Tides in the Martian Middle Atmosphere
The first systematic observations of the middle atmosphere of Mars with the Mars Climate Sounder show dramatic patterns of diurnal thermal variation. At the time of writing, the data are sufficient for spectral analysis within a limited range of latitudes and seasons. This analysis shows that these thermal variations are almost exclusively associated with a diurnal thermal tide. Using a Martian General Circulation Model as a proxy for the data, we show that the diurnal thermal tide dominates these patterns for all latitudes and all seasons. We discuss the seasonal dependence of the tidal structure in relation to the atmospheric circulation, and we examine the decrease in tidal amplitude (in the GCM) during southern summer.
P51B-1412
The Martian Atmosphere as Observed by VIRTIS-M on Rosetta Spacecraft
The Rosetta spacecraft performed a flyby of Mars on its way to 67P/Churyumov-Gerasimenkoin February 25th, 2007. This event provided a unique opportunity to test the spacecraft and instrument status, and to acquire a scientifically highly valuable set of observations. In this paper we describe the measurements performed by the M-channel of Visual and Infrared Thermal Imaging Spectrometer (VIRTIS), and the first scientific results derived from their analysis. The VIRTIS-M instrument is a spectro-imager operating in the range 0.25-5 μm, with a spectral resolution of 10 nm in IR. The radiation emerging from the Martian atmosphere in this spectral range keeps record of a wide range of phenomena that can be effectively studied thanks to the accurate absolute radiometric calibration of the instrument. The range 3-5 μm is dominated by the thermal emission of the surface and the atmosphere. Namely, it is possible to exploit the variations of CO2 adsorbing coefficients in the 4.3 μm complex to constrain – from VIRTIS nighttime data - the air temperature profile in the lower atmosphere (5-30 km). The comparison of VIRTIS data with state-of-the-art Global Circulation Models shows as a general trend slight temperature excess accompanied by the presence of a wide equatorial regions with moderate deficiencies (~5K), possibly related to the occurrence of water ice clouds. Daytime data of the same spectral regions are dominated by CO2 non-LTE emission in the high atmosphere. A mapping of emission intensity confirms the strict dependence against sun zenith angle expected by theoretical models. Devoted limb observations also allow to retrieve, by a simple onion-peeling technique, the vertical profile of emission intensity that peaks around 105 km in southern tropical regions. Ozone content can be effectively monitored by the emission of O2 (a1Δg) at 1.27 μm, which is produced by dissociation of O3. A zero order correction for the intensity of incoming solar flux shows that polar regions are particularly rich in ozone, consistently with the expected anti correlation with water vapor content. Limb observations indicate how ozone emission in the South tropical region remains above the noise level at least up to 90 km. Nighttime oxygen emission was also observed above the North polar region. Aerosol scattering was observed in the 1-2.5 μm region above the night disk, pointing toward the occurrence of very high noctilucent clouds. Limb observation of aerosol species is quite complex to model, due to numerical difficulties in the treatment of anisotropic multiple scattering on spherical shells representation. Images at the highest spatial resolution available suggest however a meaningful aerosol occurrence up to 140 km above the surface.
P51B-1413
Turbulence in the Martian Atmosphere from Mars Express Radar Sounding
The MARSIS ionospheric sounder aboard the ESA spacecraft Mars Express yields a measurement of the peak plasma frequency, and therefore, the peak electron density of the Martian ionosphere, to a precision of about two percent. It is therefore a good index of plasma variations in the Martian ionosphere at frequencies less than the Nyquist frequency, about 0.07 Hz. Similarly, the peak altitude, computed by inverting ionospheric traces to get electron density profiles, can be used to index vertical variation in the Martian ionosphere. Finally, we can use the electron density profiles to obtain the variation of the density at a given altitude. We have chosen to make this computation at an altitude of 200 km. Using about 300 orbits for which we have continuous data near periapsis, we have done spectral analyses of the wave power in these quantities and have then fit the resulting spectra to a power law. For all of the above named quantities, the power law index is distributed between -2.0 and 0.0, with a strong maximum at a value slightly more negative than -5/3, the value of the index typical of Kolmogorov turbulence. Thus, we conclude that the Martian ionosphere and atmosphere are partially dominated by isotropic incompressive turbulence.
P51B-1414
Connection of the mountain clouds on Mars with the local dynamics using a Mars GCM
Discrete afternoon mountain clouds are one of the early atmospheric features observed on Mars. Their exclusive formation near the high mountains led to the assumption that air lifting associated with local circulation forced by the mountains is behind their formation. The mountain clouds are regularly seen over the high mountains on Mars such as the soaring Tharsis volcanoes, the giant Olympus Mons that peaks at 21.1 km high and Elysium Mons, but also over moderately elevated mountains like Alba Patera (6.8 km) and Apollinaris Patera (5 km). They acquire their distinctive character from being associated with mountain peaks and regularly appearing in daytime in the northern spring and summer seasons when other clouds are rare to observe. Using a general circulation model of the atmosphere of Mars we investigate the local dynamics that lead to the formations of mountain clouds and their connection to the amounts of water present in the atmosphere and to the aphelion cloud belt.
P51B-1415
Desert dust in the atmospheres of Earth and Mars.
The Phoenix Mars lidar was successfully operated through 90 sols of the primary mission, and provide both spatial and temporal data on the distribution of Aeolian scatterers in the Martian atmosphere. Measurements were obtained at a variety of times throughout the diurnal cycle, and show a pattern early in the mission of enhanced scattering signal at the top of the dust boundary layer during the afternoon. Similar features were observed in November of 2007 in the Australian desert with an analogous lidar system, and simultaneous in situ aircraft measurements indicate that such signal enhancements correlate with periods of increased relative humidity. The vertical water content distribution in the Martian atmosphere during such events was thus considered in the context of lidar scattering signals, and a comparison of both Martian and Terrestrial results will be presented.
P51B-1416
Charge Distribution in Martian Dust Disturbances
Dust charging studies using Mars soil simulant suggest that the triboelectric charging of dust observed within terrestrial dust disturbances is also very likely on Mars. Most charging occurs within the first few centimeters of the surface; some of these grains are then injected further into the air where they are transported upward by atmospheric currents. Differential transport and gravitational sedimentation sorts the dust devil aerosols by size so that the lighter and predominantly negatively charged particles populate the higher portion of the disturbance while the heavier, positively charged particles fall to the ground or remain in the lower portion of the vortex. We have modified the Mars Regional Atmospheric Modeling System (MRAMS) to include charge distribution as a function of dust particle size and composition. An analytic representation of the charge distribution is derived based on the individual particle charge values provided by the Macroscopic Triboelectric Simulation (MTS) code. Initial model results will be presented covering a range of parameter space including wind speed and shear, dust size distribution at the surface, Weibull wind speed PDF distribution width, and dust composition.
P51B-1417
Validating Habitability Assessment of Mars Soils: Life at the Soil-Ice Boundary in the Antarctic Dry Valleys
Recent results from the Phoenix Mars Lander revealed that, similar, to the dry permafrost/ice table region in high elevation Antarctic Dry Valleys (ADV), atmosphere just above the permanent ground ice on Mars is also saturated with water vapor and the soils above it bear a remarkable visual resemblance to the dry permafrost of the high ADV, without implying they are compositionally the same material. We hypothesized that if microorganisms are found in the ice table region of the ADV and this region is proven similar to the analogous site on Mars, we can argue for habitability of Mars soils. With this in mind, we undertook a study of ice table microbial ecology in soils collected from the ADV and spanning a range of climate regimes. These findings are from a preliminary microbiological investigation and combine microscopy, phylogenetic analysis, geochemistry, mineralogy and field observations. Our microbiological study is an addendum to an IPY project detailing soil characteristics and making in situ measurements with Earth analogue Phoenix Lander instruments. We found that both low elevation 'wet permafrost' and high elevation 'dry permafrost' ADV soils had low but significant numbers of bacteria present at the ice table surface but the types of organisms and their distribution in the soil profile reflected prevailing environmental conditions at each site. We will present our detailed analyses and we suggest, that, based on this preliminary study, the idea of using microbes as indicators of habitability, when tied to environmental parameters such as climate, soil chemistry, mineralogy, and structure as well as local geology, is a feasible way to test hypotheses of what constitutes a habitable environment on Mars.
P51B-1418
Stereo specificity in substrate utilization: a new Martian life detection approach
The Viking biological investigation of Mars yielded controversial results. On the one hand it showed that Martian soil can decompose carbohydrates and amino acids as if it contained microorganisms. On the other hand, soil analysis revealed no indigenous organic carbon, suggesting that inorganic oxidants, such as hydrogen peroxide, may be responsible for the destruction of the added organics. One proposal for testing the two hypotheses calls for the use of pure isomers of organic nutrients. The selective destruction of one isomer would indicate biological activity, whereas the destruction of both isomers would indicate abiotic redox processes. This study provides experimental verification for this life detection scheme. Selected eukaryotes, bacteria, and archaea take up and utilize only D-glucose, not L-glucose. In contrast, chemical oxidation by permanganate destroys both D- and L-glucose. These findings, if replicated with more organisms, may justify a new in situ experiment on Mars to clarify the nature of its soil reactivity.