[meteorite-list] NASA's Curiosity Eyes Prominent Mineral Veins on Mars

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4536

NASA's Curiosity Eyes Prominent Mineral Veins on Mars
Jet Propulsion Laboratory
April 1, 2015

Fast Facts:

* Exposed mineral veins at "Garden City" tell of a wet environment after 
lake-bed deposits became rock

* Drilled sample from "Telegraph Peak" contains cristobalite, a silica 
mineral

Two-tone mineral veins at a site NASA's Curiosity rover has reached by 
climbing a layered Martian mountain offer clues about multiple episodes 
of fluid movement. These episodes occurred later than the wet environmental 
conditions that formed lake-bed deposits the rover examined at the mountain's 
base.

Curiosity has analyzed rock samples drilled from three targets lower on 
the mountain in the past seven months. It found a different mineral composition 
at each, including a silica mineral named cristobalite in the most recent 
sample. These differences, together with the prominent veins seen in images 
taken a little farther uphill, illustrate how the layers of Mount Sharp 
provide a record of different stages in the evolution of the area's ancient 
environment.

The two-tone veins are at the site called "Garden City." They appear as 
a network of ridges left standing above the now eroded-away bedrock in 
which they formed. Individual ridges range up to about 2.5 inches (6 centimeters) 
high and half that in width, and they bear both bright and dark material.

"Some of them look like ice-cream sandwiches: dark on both edges and white 
in the middle," said Linda Kah, a Curiosity science-team member at the 
University of Tennessee, Knoxville. "These materials tell us about secondary 
fluids that were transported through the region after the host rock formed."

Veins such as these form where fluids move through cracked rock and deposit 
minerals in the fractures, often affecting the chemistry of the rock surrounding 
the fractures. Curiosity has found bright veins composed of calcium sulfate 
at several previous locations. The dark material preserved here presents 
an opportunity to learn more. Kah said, "At least two secondary fluids 
have left evidence here. We want to understand the chemistry of the different 
fluids that were here and the sequence of events. How have later fluids 
affected the host rock?"

Some of the sequence is understood: Mud that formed lake-bed mudstones 
Curiosity examined near its 2012 landing site and after reaching Mount 
Sharp must have dried and hardened before the fractures formed. The dark 
material that lines the fracture walls reflects an earlier episode of 
fluid flow than the white, calcium-sulfate-rich veins do, although both 
flows occurred after the cracks formed.

Garden City is about 39 feet (12 meters) higher than the bottom edge of 
the "Pahrump Hills" outcrop of the bedrock forming the basal layer of 
Mount Sharp, at the center of Mars' Gale Crater. The Curiosity mission 
spent about six months examining the first 33 feet (10 meters) of elevation 
at Pahrump Hills, climbing from the lower edge to higher sections three 
times to vertically profile the rock structures and chemistry, and to 
select the best targets for drilling.

"We investigated Pahrump Hills the way a field geologist would, looking 
over the whole outcrop first to choose the best samples to collect, and 
it paid off," said David Blake of NASA's Ames Research Center, Moffett 
Field, California, principal investigator for the Chemistry and Mineralogy 
(CheMin) analytical laboratory instrument inside the rover.

Analysis is still preliminary, but the three drilled samples from Pahrump 
Hills have clear differences in mineral ingredients. The first, "Confidence 
Hills," had the most clay minerals and hematite, both of which commonly 
form under wet conditions. The second, "Mojave," had the most jarosite, 
an oxidized mineral containing iron and sulfur that forms in acidic conditions. 
The third is "Telegraph Peak." Examination of Garden City has not included 
drilling a sample.

Blake said, "Telegraph Peak has almost no evidence of clay minerals, the 
hematite is nearly gone and jarosite abundance is down. The big thing 
about this sample is the huge amount of cristobalite, at about 10 percent 
or more of the crystalline material." Cristobalite is a mineral form of 
silica. The sample also contains a small amount of quartz, another form 
of silica. Among the possibilities are that some process removed other 
ingredients, leaving an enrichment of silica behind; or that dissolved 
silica was delivered by fluid transport; or that the cristobalite formed 
elsewhere and was deposited with the original sediment.

NASA's Mars Science Laboratory Project is using Curiosity to examine environments 
that offered favorable conditions for microbial life on ancient Mars, 
if the planet ever has hosted microbes, and the changes from those environments 
to drier conditions that have prevailed on Mars for more than three billion 
years.

After investigations in the Telegraph Peak area, the rover team plans 
to drive Curiosity through a valley called "Artist's Drive" to reach higher 
layers. Engineers are meanwhile developing guidelines for best use of 
the rover's drill, following detection of a transient short circuit last 
month while using the tool's percussion action to shake rock powder into 
a sample-processing device. Drilling can use both rotary and percussion 
actions.

"We expect to use percussion as part of drilling in the future while we 
monitor whether shorts become more frequent," said Steve Lee of NASA's 
Jet Propulsion Laboratory, Pasadena, California. Lee became deputy project 
manager for the Mars Science Laboratory Project this month. He previously 
led the project's Guidance, Navigation and Control Team from design through 
landing.

JPL, a division of the California Institute of Technology in Pasadena, 
built the rover and manages the project for NASA's Science Mission Directorate 
in Washington. For more information about Curiosity, visit:

http://www.nasa.gov/msl

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

You can follow the mission on Facebook and Twitter at:

http://www.facebook.com/marscuriosity

http://www.twitter.com/marscuriosity


Media Contact

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

Dwayne Brown
NASA Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov 

2015-113