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	This artist's rendition of the Mars Science Laboratory (MSL) landing on Mars in 2012 illustrates the new "Sky Crane" system. SwRI's Radiation Assessment Detector (RAD) is onboard.  Image courtesy of NASA/JPL

Studies of Mars span the planet’s atmosphere, surface, and interior, both past and present. Atmospheric modeling of Mars is important both for basic science and for weather forecasts critical to the successful landing and operation of spacecraft on the Martian surface.

Mars Science Laboratory

Following recent successes with predictions for the landings of the Mars Exploration Rover and Phoenix spacecraft, scientists at Southwest Research Institute (SwRI) are providing similar forecasts for the Mars Science Laboratory (MSL), a large rover scheduled to land in 2012. MSL uses a new landing system that hovers above the surface and lowers the rover on a cable. The system is sensitive to density perturbations and winds, for which observations are lacking or completely absent but which can be assessed with models that already have an excellent track record of accurate predictions.

Atmospheric Modeling

	Towering dust storms over 15 km in height bear down on one of the proposed Mars Science Laboratory (MSL) landing sites, Mawrth Valles, as simulated by the Mars Regional Atmospheric Modeling System (MRAMS). The atmospheric information provided by the model is being used to establish the safety of proposed MSL landing sites and to guide descent and landing operations.
	The Laser Desorption Resonance Ionization Mass Spectrometry (LDRIMS) Laboratory seeks to develop a compact instrument for field measurement of rock ages on Earth and other rocky planets and moons.

Atmospheric modeling is illuminating the physics of Mars’ famous dust storms. Large storms may generate electrical fields strong enough to trigger lightning, but even dust devils may produce electric fields strong enough to dissociate carbon dioxide and produce superoxides. These oxidizing molecules could be produced in high enough concentration to sterilize the surface of Mars and to rapidly destroy methane. This may help constrain whether methane is produced by biological or geochemical processes.

Use of Thermal Infrared Spectra to Detect Geologic Evolution

The thermal infrared spectra of geological materials are measured in two laboratories, where SwRI scientists are helping to develop spectral libraries of phases important to the interpretation of remote-sensing data of planetary surfaces, such as the mapping of igneous, aqueous, and weathering-derived phases on Mars and small bodies.

For example, through global-scale mapping of the igneous mineral olivine, the team inferred a broader evolution of magma compositions over time on Mars than had been previously recognized. Laboratory simulations of water-rock interactions on Mars track the evolution of the near-surface environment and suggest that magnesium sulfate salts are dominant under acidic conditions that likely are representative of early Mars. Such salts were found by NASA’s Mars Exploration Rover Opportunity. Alkaline conditions, thought to have prevailed through most of Mars’ history, produce mostly calcium sulfates in the laboratory.

Scientists also are working to understand the effects of small particle sizes and vacuum environments on infrared spectra, which will aid in the identification and numerical abundance modeling of phases on airless bodies with powdery surfaces, such as asteroids and the Moon.

Tracking Martian Climate Cycles

Below the microwave band, electromagnetic energy penetrates into the interiors of rocky and icy bodies. Signals from the Shallow Radar (SHARAD) instrument onboard NASA’s Mars Reconnaissance Orbiter were able to penetrate a 3-km-thick stack of layers in the planet’s north polar region. Staff analysis of those signals revealed a cyclical pattern of strongly reflective, layered materials, interleaved with zones of lower reflectivity. These patterns track models of Martian climate cycles for the past four million years and constrain the age, composition and atmospheric precipitation of the ice-rich layers.

Use of Electromagnetic Spectrum to Probe Solid Rock

	This cross-section of the north polar cap of Mars (a) produced by ice-penetrating radar shows internal layering, likely due to layers of dust and ice (b). Composite images of many spacecraft passes allow a map of ice thickness to be developed (c-e).

Below even radar frequencies lies the vast underworld of the electromagnetic spectrum where energy is transported by diffusion instead of as waves. Because this energy can penetrate solid rock to depths of hundreds of kilometers, it is useful for probing the structure, temperature, and composition of the interiors of solid planets and moons. Staff members are extending the limits of terrestrial geophysics and performing laboratory measurements to enable this next advance in planetary subsurface exploration. Byproducts of this work include:

• New knowledge of the structural chemistry of ice

• Soil-ice electrical interactions

• Attribution of broadband dispersion and loss in surface-penetrating radar — both on Earth and on Mars — to thin films of adsorbed water

Discovery of a Hydrologic Cycle on Mars

In contrast to the relatively small quantities of water concentrated in the polar caps and dispersed in the crust today, it has long been thought that large quantities of discharged groundwater must have shaped the early Martian surface. Adapting terrestrial hydrogeological models to Mars, SwRI scientists found that the discharged groundwater was most likely supplied by recharge on the nearby Tharsis rise, but that such connections were regional, and not global, in scale. Large lakes were intermediate reservoirs for groundwater discharge. These interactions represent a true hydrologic cycle on early Mars.

Detecting the Age of Rocks

Determining the age of a rocky surface is one of the pivotal measurements that can be made in planetary geology, yet this has been done only for samples returned by astronauts from the Moon. SwRI has a major effort under way to develop a portable Laser Desorption Resonance Ionization Mass Spectrometer (LDRIMS), a backpack-size instrument that can determine rock ages from a robotic lander or a rover. LDRIMS uses the classic method of measuring the radioactive decay of rubidium and strontium. The current benchtop prototype can measure standards with 10 parts per million net strontium to ±0.5 percent, and one-part-per-10-billion sensitivity, in less than one minute. Models of the error in the age measurement, assuming the composition of meteorites known to have come from Mars, show that dates accurate to 50 million years are possible in a few hours.

For more information about our studies of Mars, or how you can contract with SwRI, please contact Robert Grimm, Ph.D., at rgrimm@swri.org or (720) 240-0149.

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Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

December 28, 2012