'Marias Pass,' Contact Zone of Two Martian Rock Units
This May 22, 2015, view from the Mast Camera (Mastcam) in NASA's Curiosity Mars rover shows the "Marias Pass" area where a lower and older geological unit of mudstone -- the pale zone in the center of the image -- lies in contact with an overlying geological unit of sandstone.

'Big Sky' and 'Greenhorn' Drilling Area on Mount Sharp
This view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover covers an area in "Bridger Basin" that includes the locations where the rover drilled a target called "Big Sky" on the mission's Sol 1119 (Sept. 29, 2015) and a target called "Greenhorn" on Sol 1137 (Oct. 18, 2015).
In detective stories, as the plot thickens, an unexpected clue often delivers more questions than answers. In this case, the scene is a mountain on Mars. The clue: the chemical compound silica. Lots of silica. The sleuths: a savvy band of Earthbound researchers whose agent on Mars is NASA's laser-flashing, one-armed mobile laboratory, Curiosity.

NASA's Curiosity rover has found much higher concentrations of silica at some sites it has investigated in the past seven months than anywhere else it has visited since landing on Mars 40 months ago. Silica makes up nine-tenths of the composition of some of the rocks. It is a rock-forming chemical combining the elements silicon and oxygen, commonly seen on Earth as quartz, but also in many other minerals.

"These high-silica compositions are a puzzle. You can boost the concentration of silica either by leaching away other ingredients while leaving the silica behind, or by bringing in silica from somewhere else," said Albert Yen, a Curiosity science team member at NASA's Jet Propulsion Laboratory, Pasadena, California. "Either of those processes involve water. If we can determine which happened, we'll learn more about other conditions in those ancient wet environments."

Water that is acidic would tend to carry other ingredients away and leave silica behind. Alkaline or neutral water could bring in dissolved silica that would be deposited from the solution. Apart from presenting a puzzle about the history of the region where Curiosity is working, the recent findings on Mount Sharp have intriguing threads linked to what an earlier NASA rover, Spirit, found halfway around Mars. There, signs of sulfuric acidity were observed, but Curiosity's science team is still considering both scenarios -- and others -- to explain the findings on Mount Sharp.

Curiosity's Path During 2015 Studies of Silica-Rich Rocks
This map shows the route on lower Mount Sharp that NASA's Curiosity followed between April 19, 2015, and Nov. 5, 2015. During this period the mission investigated silica-rich rock targets including "Buckskin," in the "Maria Pass" area, and "Greenhorn," in the "Bridger Basin" area.
Adding to the puzzle, some silica at one rock Curiosity drilled, called "Buckskin," is in a mineral named tridymite, rare on Earth and never seen before on Mars. The usual origin of tridymite on Earth involves high temperatures in igneous or metamorphic rocks, but the finely layered sedimentary rocks examined by Curiosity have been interpreted as lakebed deposits. Furthermore, tridymite is found in volcanic deposits with high silica content. Rocks on Mars' surface generally have less silica, like basalts in Hawaii, though some silica-rich (silicic) rocks have been found by Mars rovers and orbiters. Magma, the molten source material of volcanoes, can evolve on Earth to become silicic. Tridymite found at Buckskin may be evidence for magmatic evolution on Mars.

Curiosity has been studying geological layers of Mount Sharp, going uphill, since 2014, after two years of productive work on the plains surrounding the mountain. The mission delivered evidence in its first year that lakes in the area billions of years ago offered favorable conditions for life, if microbes ever lived on Mars. As Curiosity reaches successively younger layers up Mount Sharp's slopes, the mission is investigating how ancient environmental conditions evolved from lakes, rivers and deltas to the harsh aridity of today's Mars.

Seven months ago, Curiosity approached "Marias Pass," where two geological layers are exposed in contact with each other. The rover's laser-firing instrument for examining compositions from a distance, Chemistry and Camera (ChemCam), detected bountiful silica in some targets the rover passed on its way to the contact zone. The rover's Dynamic Albedo of Neutrons instrument simultaneously detected that the rock composition was unique in this area.

Details on Silica-Rich 'Elk' Target near 'Marias Pass'
This image from the Chemistry and Camera (ChemCam) instrument on NASA's Curiosity Mars rover shows detailed texture of a rock target called "Elk" on Mars' Mount Sharp, revealing laminations that are present in much of the Murray Formation geological unit of lower Mount Sharp.
"The high silica was a surprise -- so interesting that we backtracked to investigate it with more of Curiosity's instruments," said Jens Frydenvang of Los Alamos National Laboratory in New Mexico and the University of Copenhagen, Denmark.

Gathering clues about silica was a major emphasis in rover operations over a span of four months and a distance of about one-third of a mile (half a kilometer).

The investigations included many more readings from ChemCam, plus elemental composition measurements by the Alpha Particle X-ray Spectrometer (APXS) on the rover's arm and mineral identification of rock-powder samples by the Chemistry and Mineralogy (CheMin) instrument inside the rover.

Buckskin was the first of three rocks where drilled samples were collected during that period. The CheMin identification of tridymite prompted the team to look at possible explanations: "We could solve this by determining whether trydymite in the sediment comes from a volcanic source or has another origin," said Liz Rampe, of Aerodyne Industries at NASA's Johnson Space Center, Houston. "A lot of us are in our labs trying to see if there's a way to make tridymite without such a high temperature."

Beyond Marias Pass, ChemCam and APXS found a pattern of high silica in pale zones along fractures in the bedrock, linking the silica enrichment there to alteration by fluids that flowed through the fractures and permeated into bedrock. CheMin analyzed drilled material from a target called "Big Sky" in bedrock away from a fracture and from a fracture-zone target called "Greenhorn." Greenhorn indeed has much more silica, but not any in the form of tridymite. Much of it is in the form of noncrystalline opal, which can form in many types of environments, including soils, sediments, hot spring deposits and acid-leached rocks.

Discolored Fracture Zones in Martian Sandstone
This view from NASA's Curiosity Mars rover shows an example of discoloration closely linked to fractures in the Stimson formation sandstone on lower Mount Sharp. The pattern is evident along two perpendicular fractures.
"What we're seeing on Mount Sharp is dramatically different from what we saw in the first two years of the mission," said Curiosity Project Scientist Ashwin Vasavada of JPL. "There's so much variability within relatively short distances. The silica is one indicator of how the chemistry changed. It's such a multifaceted and curious discovery, we're going to take a while figuring it out."

For more about Curiosity, which is examining sand dunes this month, visit:

http://mars.jpl.nasa.gov/msl/



  • This map shows the route driven by NASA's Curiosity Mars rover from the location where it landed in August 2012 to its location in December 2015, at examples of the Bagnold Dunes.

    This map shows the route driven by NASA's Curiosity Mars rover from the location where it landed in August 2012 to its location in December 2015, at examples of the "Bagnold Dunes." The mission's investigation targets in the "Marias Pass" and "Bridger Basin" areas included rocks with compositions high in silica.

    The traverse line covers drives...

    more
  • This map shows the route on lower Mount Sharp that NASA's Curiosity followed between April 19, 2015, and Nov. 5, 2015.

    This map shows the route on lower Mount Sharp that NASA's Curiosity followed between April 19, 2015, and Nov. 5, 2015. During this period the mission investigated silica-rich rock targets including "Buckskin," in the "Maria Pass" area, and "Greenhorn," in the "Bridger Basin" area.

    High-silica sites were identified both in the Murray formation...

    more
  • This May 22, 2015, view from the Mast Camera (Mastcam) in NASA's Curiosity Mars rover shows the "Marias Pass" area where a lower and older geological unit of mudstone -- the pale zone in the center of the image -- lies in contact with an overlying geological unit of sandstone.

    This view from the Mast Camera (Mastcam) in NASA's Curiosity Mars rover shows the "Marias Pass" area where a lower and older geological unit of mudstone -- the pale zone in the center of the image -- lies in contact with an overlying geological unit of sandstone.

    Just before Curiosity reached Marias Pass, the rover's laser-firing Chemistry and...

    more
  • This May 22, 2015, view from the Mast Camera (Mastcam) in NASA's Curiosity Mars rover shows the "Marias Pass" area where a lower and older geological unit of mudstone -- the pale zone in the center of the image -- lies in contact with an overlying geological unit of sandstone.

    This view from the Mast Camera (Mastcam) in NASA's Curiosity Mars rover shows the "Marias Pass" area where a lower and older geological unit of mudstone -- the pale zone in the center of the image -- lies in contact with an overlying geological unit of sandstone.

    Just before Curiosity reached Marias Pass, the rover's laser-firing Chemistry and...

    more
  • NASA's Curiosity Mars rover used its Navigation Camera (Navcam) to capture this view partway back down a slope it climbed toward "Marias Pass" on lower Mount Sharp.

    NASA's Curiosity Mars rover used its Navigation Camera (Navcam) to capture this view partway back down a slope it climbed toward "Marias Pass" on lower Mount Sharp. The image was taken May 22, 2015, during the 992nd Martian day, or sol, of the rover's work on Mars.

    A rock about a wheel's width to the left of the foreground wheel in this image...

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  • NASA's Curiosity Mars rover used its Navigation Camera (Navcam) to capture this view partway back down a slope it climbed toward "Marias Pass" on lower Mount Sharp.

    NASA's Curiosity Mars rover used its Navigation Camera (Navcam) to capture this view partway back down a slope it climbed toward "Marias Pass" on lower Mount Sharp. The image was taken May 22, 2015, during the 992nd Martian day, or sol, of the rover's work on Mars.

    A rock about a wheel's width to the left of the foreground wheel in this image...

    more
  • This image from the Chemistry and Camera (ChemCam) instrument on NASA's Curiosity Mars rover shows detailed texture of a rock target called "Elk" on Mars' Mount Sharp, revealing laminations that are present in much of the Murray Formation geological unit of lower Mount Sharp.

    This image from the Chemistry and Camera (ChemCam) instrument on NASA's Curiosity Mars rover shows detailed texture of a rock target called "Elk" on Mars' Mount Sharp, revealing laminations that are present in much of the Murray Formation geological unit of lower Mount Sharp.

    Researchers also used ChemCam's laser and spectrometers to assess...

    more
  • This view from NASA's Curiosity Mars rover shows an example of discoloration closely linked to fractures in the Stimson formation sandstone on lower Mount Sharp.

    This view from NASA's Curiosity Mars rover shows an example of discoloration closely linked to fractures in the Stimson formation sandstone on lower Mount Sharp. The pattern is evident along two perpendicular fractures.

    Curiosity's Navigation Camera (Navcam) acquired the component images of this mosaic on Aug. 23, 2015, during the 1.083rd...

    more
  • This 360-degree panorama shows the "Marias Pass" area, at center, and part of the slope that NASA's Curiosity Mars rover climbed to get there, at right.

    This 360-degree panorama shows the "Marias Pass" area, at center, and part of the slope that NASA's Curiosity Mars rover climbed to get there, at right.

    The scene combines multiple images taken by Curiosity's Navigation Camera (Navcam) on May 22, 2105, during the 992nd Martian day, or sol, of the rover's work on Mars. North is at both ends;...

    more
  • This image from NASA's Curiosity Mars rover reveals details of a bedrock discoloration pattern at a site between "Marias Pass" and "Bridger Basin."

    This image from NASA's Curiosity Mars rover reveals details of a bedrock discoloration pattern at a site between "Marias Pass" and "Bridger Basin." The discoloration is not associated with individual layers. It crosses layers and shows clear horizontal boundaries to the darker toned bedrock. This suggests it is related to alteration by fluids...

    more
  • This view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover covers an area in "Bridger Basin" that includes the locations where the rover drilled a target called "Big Sky" on the mission's Sol 1119 (Sept. 29, 2015) and a target called "Greenhorn" on Sol 1137 (Oct. 18, 2015).

    This view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover covers an area in "Bridger Basin" that includes the locations where the rover drilled a target called "Big Sky" on the mission's Sol 1119 (Sept. 29, 2015) and a target called "Greenhorn" on Sol 1137 (Oct. 18, 2015).

    The scene combines portions of several observations taken...

    more
  • This view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover covers an area in "Bridger Basin" that includes the locations where the rover drilled a target called "Big Sky" on the mission's Sol 1119 (Sept. 29, 2015) and a target called "Greenhorn" on Sol 1137 (Oct. 18, 2015).

    This view from the Mast Camera (Mastcam) on NASA's Curiosity Mars rover covers an area in "Bridger Basin" that includes the locations where the rover drilled a target called "Big Sky" on the mission's Sol 1119 (Sept. 29, 2015) and a target called "Greenhorn" on Sol 1137 (Oct. 18, 2015).

    The scene combines portions of several observations taken...

    more
  • The graph at right presents information from the NASA Curiosity Mars rover's onboard analysis of rock powder drilled from the "Buckskin" target location, shown at left.

    The graph at right presents information from the NASA Curiosity Mars rover's onboard analysis of rock powder drilled from the "Buckskin" target location, shown at left.

    X-ray diffraction analysis of the Buckskin sample inside the rover's Chemistry and Mineralogy (CheMin) instrument revealed the presence of a silica-containing mineral named...

    more
  • The graph at right presents information from the NASA Curiosity Mars rover's onboard analysis of rock powder drilled from the "Big Sky" and "Greenhorn" target locations, shown at left.

    The graph at right presents information from the NASA Curiosity Mars rover's onboard analysis of rock powder drilled from the "Big Sky" and "Greenhorn" target locations, shown at left.

    X-ray diffraction analysis of the Greenhorn sample inside the rover's Chemistry and Mineralogy (CheMin) instrument revealed an abundance of silica in the form of...

    more
  • This graph presents information from the NASA Curiosity Mars rover's onboard analysis of rock powder drilled from the "Buckskin" and "Greenhorn" target locations on lower Mount Sharp.

    This graph presents information from the NASA Curiosity Mars rover's onboard analysis of rock powder drilled from the "Buckskin" and "Greenhorn" target locations on lower Mount Sharp.

    Buckskin, in the "Marias Pass" area, and Greenhorn, in the "Bridger Basin" area, both contain high concentrations of silica. X-ray diffraction analysis of powered...

    more
  • The yellow triangles on this graph indicate concentrations of the elements titanium and silicon in selected rock targets with high silica content analyzed by the Alpha Particle X-ray Spectrometer (APXS) instrument on NASA's Curiosity rover in Mars' Gale Crater.

    The yellow triangles on this graph indicate concentrations of the elements titanium and silicon in selected rock targets with high silica content analyzed by the Alpha Particle X-ray Spectrometer (APXS) instrument on NASA's Curiosity rover in Mars' Gale Crater.

    The pattern shows a correlation between enriched silicon content and enriched...

    more
  • NASA's Curiosity Mars rover examined both the "Greenhorn" and "Big Sky" targets with the rover's Alpha Particle X-ray Spectrometer (APXS) instrument.

    NASA's Curiosity Mars rover examined both the "Greenhorn" and "Big Sky" targets with the rover's Alpha Particle X-ray Spectrometer (APXS) instrument. Greenhorn is located within an altered fracture zone and has an elevated concentration of silica (about 60 percent by weight). Big Sky is the unaltered counterpart for comparison.

    The bar plot on...

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  • This graph shows the ratio of concentrations of several elements in four different pairs of targets examined by Alpha Particle X-ray Spectrometer (APXS) instruments on NASA Mars rovers Curiosity and Spirit.

    This graph shows the ratio of concentrations of several elements in four different pairs of targets examined by Alpha Particle X-ray Spectrometer (APXS) instruments on NASA Mars rovers Curiosity and Spirit.

    For each pair of targets, one shows evidence of mineral alteration and the other is an unaltered counterpart. The first three pairs (with...

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2015-377

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster@jpl.nasa.gov

Dwayne Brown / Laurie Cantillo
NASA Headquarters, Washington
202-358-1726 / 202-358-1077
dwayne.c.brown@nasa.gov / laura.l.cantillo@nasa.gov

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