New analyses of Martian chemical maps suggest water bound to sulfates in soil

Water (above) and sulfur (below) mass fractions found within the martian soil are mapped up to about 30-40 cm deep at hundreds of kilometer regional scales.

A research team led by LSU Geology and Geophysics Assistant Professor Suniti Karunatillake reveals a spatial association between the presence of sulfur and hydrogen found in martian soil. The work by this multi-institutional team of researchers from Georgia Tech (James Wray), Stony Brook University (Scott McLennan and Deanne Rogers), CNRS/ Université Fédérale Toulouse Midi-Pyrénées (Olivier Gasnault), Cornell University (Steve Squyres), and University of Arizona (William Boynton) may in turn identify hydrous iron sulfates as key carriers of H₂O in bulk martian soil. The gamma spectral signature of hydrogen serves as a possible indicator of water, a primary driver of weathering and life processes on Earth. The analyzed elemental data from the Gamma Ray Spectrometer onboard the Mars Odyssey orbiter was published in Geophysical Research Letters on Nov. 22, 2014.

The study indicates that within the southern latitudes of Mars, sulfur compounds are a key hydrated phase. This is revealed in part by water-to-sulfur molar ratios that fall within expected ranges corresponding to hydrated sulfate compounds. Reinforcing the data, hydrogen and sulfur correlate compellingly in the southern latitudes. The molar ratios were observed over 80 percent of Mars' southern hemisphere. Consequently, sulfate compounds, acting as primary contributors of H₂O, may also influence modern water-driven processes on Mars.

"Sulfur variation plays an important role as a control on inferred fluid pH, alteration environments, and water activity while the variation in hydration state reinforces the compelling possibility of H₂O bound primarily in sulfates in the southern hemisphere," Karunatillake said. "This applies specifically to bulk soil at decimeter depths, including the possibility that geochemical processes of iron sulfate-rich Paso Robles soil in Gusev Crater may have been more common at regional scales in ancient martian terrain than previously appreciated."

The team suggests that further observations by the Curiosity rover in Gale Crater could move forward models of aqueous processes on Mars. For example, recent analyses of "Rocknest" soil samples suggest complementary modes of soil hydration in the Gale Crater area.

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Tales from a Martian rock: New chemical analysis of ancient Martian meteorite provides clues to planet's history of habitability

The surface of Mars was once wet, but no water flows there now. UC San Diego chemists and others took a close look at meteorite that may have been blasted from this huge rift across the planet’s surface. The image is a composite of hundreds of photos taken by NASA’s Viking missions in the 1970s.

A new analysis of a Martian rock that meteorite hunters plucked from an Antarctic ice field 30 years ago this month reveals a record of the planet's climate billions of years ago, back when water likely washed across its surface and any life that ever formed there might have emerged.

Scientists from the University of California, San Diego, NASA and the Smithsonian Institution report detailed measurements of minerals within the meteorite in the early online edition of the Proceedings of the National Academy of Sciences this week.

"Minerals within the meteorite hold a snapshot of the planet's ancient chemistry, of interactions between water and atmosphere," said Robina Shaheen, a project scientist at UC San Diego and the lead author of the report.

The unlovely stone, which fell to Earth 13 thousand years ago, looked a lot like a potato and has quite a history. Designated ALH84001, it is the oldest meteorite we have from Mars, a chunk of solidified magma from a volcano that erupted four billion years ago. Since then something liquid, probably water, seeped through pores in the rock and deposited globules of carbonates and other minerals.

The carbonates vary subtly depending on the sources of their carbon and oxygen atoms. Both carbon and oxygen occur in heavier and lighter versions, or isotopes. The relative abundances of isotopes forms a chemical signature that careful analysis and sensitive measurements can uncover.

Mars's atmosphere is mostly carbon dioxide but contains some ozone. The balance of oxygen isotopes within ozone are strikingly weird with enrichment of heavy isotopes through a physical chemical phenomenon first described by co-author Mark Thiemens, a professor of chemistry at UC San Diego, and colleagues 25 years ago.

"When ozone reacts with carbon dioxide in the atmosphere, it transfers its isotopic weirdness to the new molecule," said Shaheen, who investigated this process of oxygen isotope exchange as a graduate student at the University of Heidelberg in Germany. When carbon dioxide reacts with water to make carbonates, the isotopic signature continues to be preserved.

The degree of isotopic weirdness in the carbonates reflects how much water and ozone was present when they formed. It's a record of climate 3.9 billion years ago, locked in a stable mineral. The more water, the smaller the weird ozone signal.

This team measured a pronounced ozone signal in the carbonates within the meteorite, suggesting that although Mars had water back then, vast oceans were unlikely. Instead, the early Martian landscape probably held smaller seas.

"What's also new is our simultaneous measurements of carbon isotopes on the same samples. The mix of carbon isotopes suggest that the different minerals within the meteorite had separate origins," Shaheen said. "They tell us the story of the chemical and isotopic compositions of the atmospheric carbon dioxide."

ALH84001 held tiny tubes of carbonate that some scientists saw as potential evidence of microbial life, though a biological origin for the structures has been discarded. On December 16, NASA announced another potential whiff of Martian life in the form of methane sniffed by the rover Curiosity.

Carbonates can be deposited by living things that scavenge the minerals to build their skeletons, but that is not the case for the minerals measured by this team. "The carbonate we see is not from living things," Shaheen said. "It has anomalous oxygen isotopes that tell us this carbonate is abiotic."

By measuring the isotopes in multiple ways, the chemists found carbonates depleted in carbon-13 and enriched in oxygen-18. That is, Mars's atmosphere in this era, a period of great bombardment, had much less carbon-13 than it does today.

The change in relative abundances of carbon and oxygen isotopes may have occurred through extensive loss of Martian atmosphere. A thicker atmosphere would likely have been required for liquid water to flow on the planet's chilly surface.

"We now have a much deeper and specific insight into the earliest oxygen-water system in the solar system," Thiemens said. "The question that remains is when did planets, Earth and Mars, get water, and in the case of Mars, where did it go? We've made great progress, but still deep mysteries remain."

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NASA Goddard instrument makes first detection of organic matter on Mars

MSL Curiosity rover at "John Klein" drill site This self-portrait of NASA's Mars rover Curiosity combines dozens of exposures taken by the rover's Mars Hand Lens Imager on Feb. 3, 2013 plus three exposures taken May 10, 2013 to show two holes (in lower left quadrant) where Curiosity used its drill on the rock target "John Klein".

The team responsible for the Sample Analysis at Mars (SAM) instrument suite on NASA's Curiosity rover has made the first definitive detection of organic molecules at Mars. Organic molecules are the building blocks of all known forms of terrestrial life, and consist of a wide variety of molecules made primarily of carbon, hydrogen, and oxygen atoms. However, organic molecules can also be made by chemical reactions that don't involve life, and there is not enough evidence to tell if the matter found by the team came from ancient Martian life or from a non-biological process. Examples of non-biological sources include chemical reactions in water at ancient Martian hot springs or delivery of organic material to Mars by interplanetary dust or fragments of asteroids and comets.

The surface of Mars is currently inhospitable to life as we know it, but there is evidence that the Red Planet once had a climate that could have supported life billions of years ago. For example, features resembling dry riverbeds and minerals that only form in the presence of liquid water have been discovered on the Martian surface. The Curiosity rover with its suite of instruments including SAM was sent to Mars in 2011 to discover more about the ancient habitable Martian environment by examining clues in the chemistry of rocks and the atmosphere.

The organic molecules found by the team were in a drilled sample of the Sheepbed mudstone in Gale crater, the landing site for the Curiosity rover. Scientists think the crater was once the site of a lake billions of years ago, and rocks like mudstone formed from sediment in the lake. Moreover, this mudstone was found to contain 20 percent smectite clays. On Earth, such clays are known to provide high surface area and optimal interlayer sites for the concentration and preservation of organic compounds when rapidly deposited under reducing chemical conditions.

While the team can't conclude that there was life at Gale crater, the discovery shows that the ancient environment offered a supply of reduced organic molecules for use as building blocks for life and an energy source for life. Curiosity's earlier analysis of this same mudstone revealed that the environment offered water and chemical elements essential for life and a different chemical energy source.

"We think life began on Earth around 3.8 billion years ago, and our result shows that places on Mars had the same conditions at that time -- liquid water, a warm environment, and organic matter," said Caroline Freissinet of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "So if life emerged on Earth in these conditions, why not on Mars as well?" Freissinet is lead author of a paper on this research submitted to the Journal of Geophysical Research-Planets.

The organic molecules found by the team also have chlorine atoms, and include chlorobenzene and several dichloroalkanes, such as dichloroethane, dichloropropane and dichlorobutane. Chlorobenzene is the most abundant with concentrations between 150 and 300 parts-per-billion. Chlorobenzene is not a naturally occurring compound on Earth. It is used in the manufacturing process for pesticides (insecticide DDT), herbicides, adhesives, paints and rubber. Dichloropropane is used as an industrial solvent to make paint strippers, varnishes and furniture finish removers, and is classified as a carcinogen.

It's possible that these chlorine-containing organic molecules were present as such in the mudstone. However, according to the team, it's more likely that a different suite of precursor organic molecules was in the mudstone, and that the chlorinated organics formed from reactions inside the SAM instrument as the sample was heated for analysis. Perchlorates (a chlorine atom bound to four oxygen atoms) are abundant on the surface of Mars. It's possible that as the sample was heated, chlorine from perchlorate combined with fragments from precursor organic molecules in the mudstone to produce the chlorinated organic molecules detected by SAM.

In 1976, the Gas Chromatograph Mass Spectrometer instrument on NASA's Viking landers detected two simple chlorinated hydrocarbons after heating Martian soils for analysis (chloromethane and dichloromethane). However they were not able to rule out that the compounds were derived from the instrument itself, according to the team. While sources within the SAM instrument also produce chlorinated hydrocarbons, they don't make more than 22 parts-per-billion of chlorobenzene, far below the amounts detected in the mudstone sample, giving the team confidence that organic molecules really are present on Mars.

The SAM instrument suite was built at NASA Goddard with significant elements provided by industry, university, and national and international NASA partners.

For this analysis, the Curiosity rover sample acquisition system drilled into a mudstone and filtered fine particles of it through a sieve, then delivered a portion of the sample to the SAM laboratory. SAM detected the compounds using its Evolved Gas Analysis (EGA) mode by heating the sample up to about 875 degrees Celsius (around 1,600 degrees Fahrenheit) and then monitoring the volatiles released from the sample using a quadrupole mass spectrometer, which identifies molecules by their mass using electric fields. SAM also detected and identified the compounds using its Gas Chromatograph Mass Spectrometer (GCMS) mode. In this mode, volatiles are separated by the amount of time they take to travel through a narrow tube (gas chromatography -- certain molecules interact with the sides of the tube more readily and thus travel more slowly) and then identified by their signature mass fragments in the mass spectrometer.

The first evidence for elevated levels of chlorobenzene and dichloroalkanes released from the mudstone was obtained on Curiosity Sol 290 (May 30, 2013) with the third analysis of the Cumberland sample at Sheepbed. The team spent over a year carefully analyzing the result, including conducting laboratory experiments with instruments and methods similar to SAM, to be sure that SAM could not be producing the amount of organic material detected.

"The search for organics on Mars has been extremely challenging for the team," said Daniel Glavin of NASA Goddard, a co-author on the paper. "First, we need to identify environments in Gale crater that would have enabled the concentration of organics in sediments. Then they need to survive the conversion of sediment to rock, where pore fluids and dissolved substances may oxidize and destroy organics. Organics can then be destroyed during exposure of rocks at the surface of Mars to intense ionizing radiation and oxidants. Finally, to identify any organic compounds that have survived, we have to deal with oxychlorine compounds and possibly other strong oxidants in the sample which will react with and combust organic compounds to carbon dioxide and chlorinated hydrocarbons when the samples are heated by SAM."

As part of Curiosity's plan for exploration, an important strategic goal was to sample rocks that represent different combinations of the variables thought to control organic preservation. "The SAM and Mars Science Laboratory teams have worked very hard to achieve this result," said John Grotzinger of Caltech, Mars Science Laboratory's Project Scientist. "Only by drilling additional rock samples in different locations, and representing different geologic histories were we able to tease out this result. At the time we first saw evidence of these organic molecules in the Cumberland sample it was uncertain if they were derived from Mars, however, additional drilling has not produced the same compounds as might be predicted for contamination, indicating that the carbon in the detected organic molecules is very likely of Martian origin."

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Complex mineralogy on the Red Planet: First X-ray diffraction measurements on Mars

In 2012 the Mars Science Laboratory landed in the fascinating Gale crater. The Gale crater is of such great interest because of the 5.5 km high mountain of layered materials in the middle. This material tells an intricate story of the history of Mars, perhaps spanning much of the existence of this mysterious planet.

Once positioned, the Curiosity rover began field studies on its drive toward Aeolis Mons (also unofficially known as Mount Sharp), the central peak within the crater. Curiosity has travelled more than 9.4 km so far and during its trip up the mountain, Curiosity has begun taking samples of the mountain's lower slopes.

CheMin is one of ten instruments on or inside Curiosity, all designed to provide detailed information on the rocks, soils and atmosphere. CheMin is actually a miniaturised X-ray diffraction/X-ray fluorescence (XRD/XRF) instrument, approximately the size of a shoebox, that uses transmission geometry with an energy-discriminating CCD detector to obtain unparalleled results in quite challenging conditions.

Five samples have been analysed by CheMin so far, namely a soil sample, three samples drilled from mudstones and a sample drilled from a sandstone. Rietveld and full-pattern analysis of the XRD data have revealed a complex mineralogy, with contributions from parent igneous rocks, amorphous components and several minerals relating to aqueous alteration, for example clay minerals and hydrated sulphates. In addition to quantitative mineralogy, Rietveld refinements also provide unit-cell parameters for the major phases, which can be used to infer the chemical compositions of individual minerals and, by difference, the composition of the amorphous component. Coincidentally CheMin's first XRD analysis on Mars coincided with the 100^th anniversary of the discovery of XRD by von Laue.

So far CheMin has returned excellent diffraction data comparable in many respects with data available on Earth. It has managed this even though several aspects of the instrument, particularly its small size limit the quality of the XRD data. These limitations could, however, be improved through modification of the instrument geometry. One of the most significant issues limiting remote operation is the requirement for powder XRD of a finely powdered sample. CheMin largely surmounts this difficulty through the use of its unique sample vibration device.

Data obtained so far has already provided new insights into processes on Mars, and the instrument promises to return data that will answer numerous questions and shed further light on the history of the Gale crater.

Work is already progressing in developing an upgraded instrument with changes in the reflection geometry. Coupled with data-processing software interface advances, we may see future improvements to non-contact diffraction analysis of the surfaces of planetary bodies.

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