Reflecting on Martian heat

A research team in Spain has used infrared spectroscopy to reveal that taking the temperature of the Red Planet is not quite as straightforward as astronomers would like to think. They have demonstrated that the mineralogical chemistry of the planet's surface can influence the precise temperature readings obtained for Martian soil.

The work by María Paz Martín of the CSIC-INTA Astrobiology Centre in Madrid, published in the current issue of the Journal of Environmental Monitoring will be used to interpret data from the soil temperature sensor on NASA's Mars Science Laboratory (MSL) vehicle, which is scheduled to launch in 2011.

The team selected and prepared samples of various terrestrial minerals which are known to exist on Mars, such as oxides, oxi/hydroxides, sulfates, chlorides, opals, and clays. The Martian soil is made up of a mix of dust containing basaltic materials well as oxides, such as haematite, hydrated phyllosilicates, sulfate salts, and quartzofeldspathic materials. The team obtained their Martian dust surrogate from reference materials from the United States Geological Survey, as well as from different areas of the Earth similar to those of the red planet, like El Jaroso (Almería), the Tinto River (Huelva) and Atacama Desert (Chile).

The minerals were crushed to an average particle size of 45 micrometres, which corresponds to known particulates in Martian soil. They then mixed their earthly dust in various proportions with basalt, the most important volcanic rock on Mars.

They then used Fourier transform infrared (FTIR) reflectance to record the spectra of the various blends at wavelength levels equivalent to those that will be used by the Rover Environmental Monitoring Station soil temperature sensor. REMS, which was developed by CSIC-INTA in collaboration with EADS-Crisa, the Universidad Politécnica de Cataluña, the Finnish Meteorological Institute, NASA Ames Research Center, the University of Michigan, the Universidad de Alcalá and the California Institute of Technology, will measure ambient pressure, humidity, wind speed and direction, ultraviolet radiation, and air and ground temperature on Mars, the researchers explain.

The results showed important percentage increases or decreases of reflectance across the entire wavelength range from the basalt-haematite mix to the basalt-magnetite dust. The team also observed variations that were limited to certain spectral bands, such as the basalt-smectite as opposed to the basalt-jasper blends. The team explains that the basalt reflectance percentage increases or decreases by as much 100% depending on the specific ratio of minerals present in the sample.

Because the IR spectrometers register how the different mixtures of minerals reflect infrared radiation, this information can be used to calculate the environmental temperature by REMS's onboard instruments.

"Our experiments confirm that any chemical-mineralogical analytical development on Mars requires the prior satisfactory quality of the methodological tests and routines on Earth", Martin says, "We have confirmed that the chemical-mineralogical associations on the surface of Mars influence the measuring of the temperature of the Martian soil". In other words, to measure the surface temperature with precision requires specific information about the minerals present in the Martian soil.

Team member Jesús Martínez Frías says that the results will have implications for studying water on Mars or in the search for the search for life as the reflectance data may act as indicators. He adds that the research "opens up a new line of work which will grow with the incorporation of new minerals," that will allow analyses of samples even more closely resembling actual Martian soil. Indeed, in the introduction to their paper, the team explains that, "The current Mars exploration roadmap is characterized by the emerging concept of 'habitability', which is mainly marked by the classical 'follow-the-water strategy', the additional physical-chemical information that minerals and their paragenetic associations offer about the past and present Martian environmental systems, and the search for biomarkers."

A similar approach could be used to study remotely other planets and to validate results from other explorations. The team also adds that it might be used for solid waste deposit profiles, remote sensing and monitoring studies regarding disaggregation of rocks through thermal fatigue, ecotoxicological studies of sediments from marine environments and, environmental mineralogy in general.

"This study is not only important for the calibration of the ground-temperature sensor, we are also making specific standards for different mineralogical-chemical combinations and experimentally 'forecasting' possible scientific results and paragenetic scenarios which will be useful during the mission," Frías revealed to SpectroscopyNOW. "Of course, the research is in progress, and now we are going to use specific simulation chambers to emulate the Martian conditions and to incorporate new minerals, such as carbonates.