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While NASA imagery has shown evidence of ancient rivers and lakes on Mars that transitioned to dry dunes, uncertainty remains over the timing of the environmental changes that may have contributed to these shifts. <\/p>\n
Now, data collected by NASA\u2019s Curiosity rover has revealed that individual crystals in the iron oxide hematite can be used as a mineralogical marker of changes to Mars\u2019 ancient climate. Because the shape and structure of these crystallites reflect the conditions \u2013 such as temperature and water presence \u2013 under which they were formed, they can serve as an indicator of when these changes occurred.<\/p>\n
Scientists studied 20 samples collected by Curiosity across various elevations throughout Gale Crater for a paper published Thursday in Science. Gale Crater\u2019s walls reveal Mars\u2019 environmental history layer by layer, with deeper elevations capturing its earliest years. The team analyzed data from the rover\u2019s Chemistry and Minerology (CheMin) instrument and discovered that hematite showed different crystallite sizes at different elevations. They also discovered that goethite, a mineral that typically forms alongside hematite, was absent in samples from lower elevations but still present in samples from higher elevations. This suggests that warm groundwater might have remained for up to 4.7 million years in the deepest layers of Gale Crater and that during much of this time, these long-lived aquifers could have been potentially habitable.<\/p>\n
\u201cWhat we found was that warm and wet conditions were present for extended periods in buried rocks, despite Mars\u2019 climate becoming colder,\u201d said Tanya Peretyazhko, co-first author of the study and planetary scientist in the Astromaterials Research and Exploration Science division at NASA\u2019s Johnson Space Center in Houston. \u201cIt means that deep in those rocks, those warmer conditions could have made for habitable conditions for much longer periods of time, provided that other essential factors were present.\u201d<\/p>\n
Iron oxides are considered indicators of water activity because they form in its presence. This study shows that hematite can also be a marker of climate changes based on its crystallite sizes and structures, which change under different temperatures. The scientists found that hematite crystallites from higher elevations in Gale Crater were less than 10 nanometers in size, while crystallites from lower locations were generally larger, reaching up to 65 nanometers. These findings aligned with the observations that samples from higher elevations contained both hematite and goethite, while lower elevation samples lacked goethite.<\/p>\n
Tanya Peretyazhko<\/p>\n
Planetary Scientist<\/p>\n<\/p><\/div>\n<\/p><\/div>\n<\/p><\/div>\n<\/p><\/div>\n<\/p><\/div>\n<\/div>\n
They concluded that, under warmer conditions when the pH of water is neutral or slightly alkaline, goethite can transform into hematite. These warmer conditions also favored an increase in hematite crystallite size in the deeper layers of Gale Crater through a process known as Ostwald ripening, in which smaller crystallites dissolve and contribute to the growth of larger ones.<\/p>\n
\u201cThis can tell you that the top layers were colder and didn\u2019t have enough water, or the water presence was relatively short-lived, so the crystallites didn\u2019t have sufficient time and conditions to grow in size,\u201d said Peretyazhko. \u201cBut the lower layers had longstanding warm water that allowed those crystallites to grow.\u201d<\/p>\n
A unique highlight of this study is that the data comes from Martian samples, rather than from theoretical modeling. Curiosity\u2019s robotic arm delivered powdered rock to CheMin\u2019s input funnel, where it was analyzed. \u201cWith CheMin\u2019s X-ray diffraction patterns, we can look at the hematite crystal\u2019s size and dimensions, information that that can\u2019t be gathered from satellite analysis of the Martian surface.\u201d said Tom Bristow, principal investigator of the CheMin instrument at NASA\u2019s Ames Research Center in California\u2019s Silicon Valley.<\/p>\n
Ashwin Vasavada, Curiosity\u2019s project scientist at NASA\u2019s Jet Propulsion Laboratory in Southern California, said CheMin is capable of making measurements with extraordinary scientific fidelity.<\/p>\n
\u201cIt doesn\u2019t just tell you there is hematite,” Vasavada explained. “One can use the data to extract the size and shape of the hematite crystallites and the presence of other related minerals, all of which were necessary to produce this result.\u201d<\/p>\n
More about Curiosity<\/strong><\/p>\n Curiosity was built by NASA JPL, which is managed by Caltech in Pasadena, California. NASA JPL leads the mission on behalf of NASA\u2019s Science Mission Directorate in Washington as part of NASA\u2019s Mars Exploration Program portfolio. CheMin, led by NASA Ames , is one of 10 science instruments aboard Curiosity and has a cross-country team of scientists, including researchers at NASA Ames, University of Arizona, California Institute of Technology, Planetary Science Institute, Carnegie Institution for Science, Lunar and Planetary Institute, JPL, NASA\u2019s Goddard Space Flight Center in Greenbelt, Maryland, and NASA\u2019s Johnson. The team combines expertise in mineralogy, petrology, materials science, astrobiology and soil science, with experience studying terrestrial, lunar and Martian rocks.<\/p>\n For more information on NASA\u2019s Curiosity rover, visit:<\/p>\n <\/em><\/strong><\/p>\n Karen Fox \/ Alana Johnson<\/strong>
Headquarters, Washington
240-285-5155 \/ 202-672-4780
karen.c.fox@nasa.gov \/ alana.r.johnson@nasa.gov<\/p>\n