NASA Instrument Will Identify Clues to Martian Past

NASA Instrument Will Identify Clues to Martian Past

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http://www.jpl.nasa.gov/news/news.cfm?release=2010-213&cid=release_2010-213

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."

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