[meteorite-list] NASA Instrument Will Identify Clues to Martian Past (CheMin)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 28 Jun 2010 12:29:26 -0700 (PDT)
Message-ID: <201006281929.o5SJTQEU002717_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-213

NASA Instrument Will Identify Clues to Martian Past
Jet Propulsion Laboratory
June 28, 2010

NASA's Curiosity rover, coming together for a late 2011 launch to Mars,
has a newly installed component: a key onboard X-ray instrument for
helping the mission achieve its goals. Researchers will use Curiosity in
an intriguing area of Mars to search for modern or ancient habitable
environments, including any that may have also been favorable for
preserving clues about life and environment.

The team assembling and testing Curiosity at NASA's Jet Propulsion
Laboratory, Pasadena, Calif., fastened the Chemistry and Mineralogy
(CheMin) instrument inside the rover body on June 15. CheMin will
identify the minerals in samples of powdered rock or soil that the
rover's robotic arm will deliver to an input funnel. "Minerals give us a
record of what the environment was like at the time they were formed,"
said the principal investigator for CheMin, David Blake of NASA's Ames
Research Center, Moffett Field, Calif. Temperature, pressure, and the
chemical ingredients present -- including water -- determine what
minerals form and how they are altered.

The instrument uses X-ray diffraction, a first for a mission to Mars and
a more definitive method for identifying minerals than any instrument on
previous missions. It supplements the diffraction measurements with
X-ray fluorescence capability to garner further details of composition.
X-ray diffraction works by directing an X-ray beam at a sample and
recording how the X-rays are scattered by the sample's atoms. All
minerals are crystalline, and in crystalline materials, atoms are
arranged in an orderly, periodic structure, causing the X-rays to be
scattered at predictable angles. From those angles, researchers can
deduce the spacing between planes of atoms in the crystal. "You get a
series of spacings and intensities for each mineral," Blake said. "It's
more than a fingerprint because it not only provides definitive
identification, but we know the reason for each pattern, right down to
the atomic level."

NASA's Mars Science Laboratory mission will send Curiosity to a place on
Mars where water-related minerals have been detected by Mars orbiters.
The rover's 10 science instruments
<http://msl-scicorner.jpl.nasa.gov/Instruments/> will examine the site's
modern environment and geological clues to its past environments. NASA's
multi-step strategy might include potential future missions for bringing
Mars samples to Earth for detailed analysis. One key goal for the Mars
Science Laboratory mission is to identify a good hunting ground for
rocks that could hold biosignatures -- evidence of life -- though this
mission itself will not seek evidence of life.

On Earth, life has thrived for more than 3 billion years, but preserving
evidence of life from the geologically distant past requires specific,
unusual conditions.

Fossil insects encased in amber or mastodon skeletons immersed in tar
pits are examples of how specific environments can store a record of
ancient life by isolating it from normal decomposition. But Mars won't
have insects or mastodons; if Mars has had any life forms at all, they
were likely microbes. Understanding what types of environments may have
preserved evidence of microbial life from billions of years ago, even on
Earth, is still an emerging field of study. Some factors good for life
are bad for preserving biosignatures. For example, life needs water, but
organic compounds, the carbon-chemical ingredients of life, generally
oxidize to carbon dioxide gas if not protected from water.

Some minerals detectable by CheMin, such as phosphates, carbonates,
sulfates and silica, can help preserve biosignatures. Clay minerals trap
and preserve organic compounds under some conditions. Some minerals that
form when salty water evaporates can encase and protect organics, too.
Other minerals that CheMin could detect might also have implications
about past conditions favorable to life and to preservation of
biosignatures.

"We'll finally have the ability to conduct a wide-ranging inventory of
the minerals for one part of Mars," said John Grotzinger of the
California Institute of Technology in Pasadena, chief scientist for the
Mars Science Laboratory. "This will be a big step forward. Whatever we
learn about conditions for life, we'll also get a great benefit in
learning about the early evolution of a planet."

Curiosity's 10 science instruments, with about 15 times more mass than
the five-instrument science payload on either of the Mars rovers Spirit
or Opportunity, provide complementary capabilities for meeting the
mission's goals. Some will provide quicker evaluations of rocks when the
rover drives to a new location, helping the science team choose which
rocks to examine more thoroughly with CheMin and the Sample Analysis at
Mars (SAM) experiment. SAM can identify organic compounds. Imaging
information about the context and textures of rocks will augment
information about the rocks' composition.

"CheMin will tell us the major minerals there without a lot of debate,"
said Jack Farmer of Arizona State University, Tempe, a member of the
instrument's science team. "It won???t necessarily reveal anything
definitive about biosignatures, but it will help us select the rocks to
check for organics. X-ray diffraction is the gold standard for
mineralogy. Anyone who wants to determine the minerals in a rock on
Earth takes it to an X-ray diffraction lab."

Blake began working 21 years ago on a compact X-ray diffraction
instrument for use in planetary missions. His work with colleagues has
resulted in commercial portable instruments for use in geological field
work on Earth, as well as the CheMin instrument. The spinoff instruments
have found innovative applications in screening for counterfeit
pharmaceuticals in developing nations and analyzing archaeological finds.

CheMin is roughly a cube 25 centimeters (10 inches) on each side,
weighing about 10 kilograms (22 pounds). It generates X-rays by aiming
high-energy electrons at a target of cobalt, then directing the X-rays
into a narrow beam. The detector is a charge-coupled device like the
ones in electronic cameras, but sensitive to X-ray wavelengths and
cooled to minus 60 degrees Celsius (minus 76 degrees Fahrenheit).

A sample wheel mounted between the X-ray source and detector holds 32
disc-shaped sample cells, each about the diameter of a shirt button and
thickness of a business card, with transparent plastic walls. Rotating
the wheel can position any cell into the X-ray beam. Five cells hold
reference samples from Earth to help calibrate the instrument. The other
27 are reusable holders for Martian samples. Samples of gritty powder
delivered by the robotic arm to CheMin's inlet funnel will each contain
about as much material as in a baby aspirin.

Each CheMin analysis of a sample requires up to 10 hours of accumulating
data while X-rays are hitting the sample. The time may be split into two
or more nights of operation.

Besides X-ray diffraction, CheMin records X-ray fluorescence data from
the analyzed material. X-ray fluorescence works by recording the
secondary X-rays generated when the atoms in the sample are excited by
the primary X-ray source. Different elements, when excited, emit
fluorescent X-rays at different and characteristic energies, so this
information indicates which elements are present. This compositional
information will supplement similar data collected by the Alpha Particle
X-ray Spectrometer on Curiosity's arm.

CheMin's team of scientists combines expertise in mineralogy, petrology,
materials science, astrobiology and soil science, with experience
studying terrestrial, lunar and Martian rocks.

The launch period for the Mars Science Laboratory will begin on Nov. 25,
2011, for a landing on Mars in August 2012. Blake's wish for results
from the Martian rock data he's already been anticipating for more than
two decades: "I hope we find something unexpected, something surprising."

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

2010-213
Received on Mon 28 Jun 2010 03:29:26 PM PDT


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