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  Water Found on Martian Soil, DSU Researcher Says


The Mars Curiosity rover has found significant traces of water in the Martian soil, according to Dr. Noureddine Melikechi, DSU professor of physics and dean of the College of Mathematics, Natural Sciences and Technology.

Scientists announced the news with a full report in the September 27 issue of the journal Science, titled "Soil Diversity and Hydration as Observed by ChemCam at Gale Crater, Mars".

Spectra measurements from the scoop walls of a location on Gale Crater dubbed as "Rocknest" are characterized with strong emissions from elemental hydrogen. Scientists believed the hydrogen measured was coming from water. This quantity also explains earlier orbital observations (neutron, gamma ray and near infrared spectroscopy) from previous Martian missions.

The research team includes scientists from the DSU Optical Science Center for Applied Research (OSCAR). Noureddine Melikechi, who is also the University vice president of research and a co-author of the Science article, said that the ChemCam instrument onboard Curiosity employs the Laser-Induced Breakdown Spectroscopy (LIBS) technique to examine the elemental content of its Martian target, the first of its kind on a planetary mission.

Dr. Melikechi said that this is a major step in the quest to attain a better understanding of Mars.  “The results of the analysis of the data collected by ChemCam during the first 100 sols (a sol is a Martian day) show the power and usefulness of laser spectroscope,” he said. “Even at 300 million kilometers from home, we are able to characterize dusts, soils and rocks in a way that was never possible before Curiosity.”

LIBS is an active analytical technique that makes use of a laser pulse to analyze materials of interest at a distance by creating a plasma, which emits photons at characteristic emission line wavelengths corresponding to the elemental composition of material.

ChemCam starts by shooting a high power laser pulse into the Martian soil and rock to be studied. The small sampling area of the ChemCam laser (~350 to 550 um) and percussional applications of 30 to 50 laser pulses on the same spot allow it to reach deeper into the target. More precise elemental analysis can be resolved as variations of components in different layers of the target soil are revealed while laser pulses drill into the target.

ChemCam showed that the Martian soils consist of two distinct types: a fine-grained type that is representative of the Martian dust all over the surface, and a coarser-grained type that corresponds to local rocks. Three groups of soil were also found by ChemCam: a mafic type (a mineral rich in magnesium and iron), a felsic type (an alkali-aluminum- and silica-rich mineral) and an intermediate type.

Hydrogen was found ubiquitous in the mafic soil, a key finding showing those water molecules are bound to the fine-grained soil particles. “This result has important implications; since mafic soil likely is widely distributed on Mars, it potentially could be the source for water,” said Melikechi.

Comparison of ChemCam results with that of Curiosity's other instruments confirms that hydrogen detected by ChemCam is most likely associated with water. Moreover, the instrument tested more than one hundred targets in Rocknest and found consistent water content regardless of the sampling area. And when Curiosity went in deeper into the soil, the same concentration of water was found in the newly unearthed soil.

There were thought to be several possible carriers for the hydrogen source: (1) adsorbed atmospheric H2O; (2) hydrated crystalline minerals, including phyllosilicates and salts; and (3) amorphous or poorly crystalline hydrated phases. Further comparisons with results from ChemMin rule out  the  first two possibilities.

More data collected by ChemCam is ready for analysis. "It is highly likely that much more information will be available, especially after Curiosity arrives at Mount Sharp," Melikechi said. "Mount Sharp is particularly interesting because it has sediment history of several billion years, which would provide valuable information about the geology and climate changes on Mars."