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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 1 Apr 2015 16:47:03 -0700 (PDT)
Message-ID: <201504012347.t31Nl3LX006087_at_zagami.jpl.nasa.gov>

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
Received on Wed 01 Apr 2015 07:47:03 PM PDT