Active, Ancient Organic Matter on Mars found by Curiosity rover Image 1: This image illustrates possible ways methane might be added to Mars atmosphere (sources) and removed from the atmosphere (sinks). NASAs Curiosity Mars rover has detected fluctuations in methane concentration in the atmosphere, implying both types of activity occur on modern Mars. Image Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan Image 2: This graphic offers comparisons between the amount of an organic chemical named chlorobenzene detected in the Cumberland rock sample and amounts of it in samples from three other Martian surface targets analyzed by NASAs Curiosity Mars rover. Image Credit: NASA/JPL-Caltech Image 3: This illustration portrays some of the reasons why finding organic chemicals on Mars is challenging. Whatever organic chemicals may be produced on Mars or delivered to Mars face several possible modes of being transformed or destroyed. Image Credit: NASA/JPL-Caltech NASAs Mars Curiosity rover has measured a tenfold spike in methane, an organic chemical, in the atmosphere around it and detected other organic molecules in a rock-powder sample collected by the robotic laboratory’s drill. This temporary increase in methane -- sharply up and then back down -- tells us there must be some relatively localized source, said Sushil Atreya of the University of Michigan, Ann Arbor, and Curiosity rover science team. There are many possible sources, biological or non-biological, such as interaction of water and rock. Researchers used Curiosity’s onboard Sample Analysis at Mars (SAM) laboratory a dozen times in a 20-month period to sniff methane in the atmosphere. During two of those months, in late 2013 and early 2014, four measurements averaged seven parts per billion. Before and after that, readings averaged only one-tenth that level. Curiosity also detected different Martian organic chemicals in powder drilled from a rock dubbed Cumberland, the first definitive detection of organics in surface materials of Mars. These Martian organics could either have formed on Mars or been delivered to Mars by meteorites. 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 NASAs Goddard Space Flight Center in Greenbelt, Maryland. So if life emerged on Earth in these conditions, why not on Mars as well? Organic molecules, which contain carbon and usually hydrogen, are chemical building blocks of life, although they can exist without the presence of life. Curiositys findings from analyzing samples of atmosphere and rock powder do not reveal whether Mars has ever harbored living microbes, but the findings do shed light on a chemically active modern Mars and on favorable conditions for life on ancient Mars. We will keep working on the puzzles these findings present, said John Grotzinger, Curiosity project scientist of the California Institute of Technology in Pasadena (Caltech). Can we learn more about the active chemistry causing such fluctuations in the amount of methane in the atmosphere? Can we choose rock targets where identifiable organics have been preserved? Researchers worked many months to determine whether any of the organic material detected in the Cumberland sample was truly Martian. Curiosity’s SAM lab detected in several samples some organic carbon compounds that were, in fact, transported from Earth inside the rover. However, extensive testing and analysis yielded confidence in the detection of Martian organics. The search for organics on Mars has been extremely challenging for the team, said Daniel Glavin of NASA Goddard. 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. Identifying which specific Martian organics are in the rock is complicated by the presence of perchlorate minerals in Martian rocks and soils. When heated inside SAM, the perchlorates alter the structures of the organic compounds, so the identities of the Martian organics in the rock remain uncertain. This first confirmation of organic carbon in a rock on Mars holds much promise, said Curiosity participating scientist Roger Summons of the Massachusetts Institute of Technology in Cambridge. Organics are important because they can tell us about the chemical pathways by which they were formed and preserved. In turn, this is informative about Earth-Mars differences and whether or not particular environments represented by Gale Crater sedimentary rocks were more or less favorable for accumulation of organic materials. The challenge now is to find other rocks on Mount Sharp that might have different and more extensive inventories of organic compounds. Researchers also reported that Curiositys taste of Martian water, bound into lakebed minerals in the Cumberland rock more than three billion years ago, indicates the planet lost much of its water before that lakebed formed and continued to lose large amounts after. SAM analyzed hydrogen isotopes from water molecules that had been locked inside a rock sample for billions of years and were freed when SAM heated it, yielding information about the history of Martian water. The ratio of a heavier hydrogen isotope, deuterium, to the most common hydrogen isotope can provide a signature for comparison across different stages of a planets history. Its really interesting that our measurements from Curiosity of gases extracted from ancient rocks can tell us about loss of water from Mars, said Paul Mahaffy, SAM principal investigator of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of a report published online this week by the journal Science The ratio of deuterium to hydrogen has changed because the lighter hydrogen escapes from the upper atmosphere of Mars much more readily than heavier deuterium. In order to go back in time and see how the deuterium-to-hydrogen ratio in Martian water changed over time, researchers can look at the ratio in water in the current atmosphere and water trapped in rocks at different times in the planet’s history. Martian meteorites found on Earth also provide some information, but this record has gaps. No known Martian meteorites are even close to the same age as the rock studied on Mars, which formed about 3.9 billion to 4.6 billion years ago, according to Curiosity’s measurements. The ratio that Curiosity found in the Cumberland sample is about one-half the ratio in water vapor in todays Martian atmosphere, suggesting much of the planets water loss occurred since that rock formed. However, the measured ratio is about three times higher than the ratio in the original water supply of Mars, based on assumption that supply had a ratio similar to that measured in Earths oceans. This suggests much of Mars original water was lost before the rock formed. In 1976, the Gas Chromatograph Mass Spectrometer instrument on NASAs 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 dont 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. Curiosity is one element of NASAs ongoing Mars research and preparation for a human mission to Mars in the 2030s. Caltech manages the Jet Propulsion Laboratory in Pasadena, California, and JPL manages Curiosity rover science investigations for NASAs Science Mission Directorate in Washington. The SAM investigation is led by Paul Mahaffy of Goddard. Two of SAM instruments key in these discoveries are the Quadrupole Mass Spectrometer, developed at Goddard, and the Tunable Laser Spectrometer, developed at JPL. NASA provided support for the development and operation of SAM. SAM-Gas Chromatograph was supported by funds from the French Space Agency (CNES). Individual team members were supported by the NASA Postdoctoral Program and the Mars Science Laboratory Participating Scientist Program. Data from these SAM experiments are archived in the Planetary Data System. The results of the Curiosity rover investigation into methane detection and the Martian organics in an ancient rock were discussed at a news briefing Tuesday at the American Geophysical Unions convention in San Francisco. The methane results are described in a paper published online this week in the journal Science by NASA scientist Chris Webster of JPL, and co-authors. A report on organics detection in the Cumberland rock by NASA scientist Caroline Freissenet, of Goddard, and co-authors, is pending publication.
Posted on: Wed, 17 Dec 2014 11:05:17 +0000
Trending Topics
Recently Viewed Topics
© 2015