Advanced NASA Instrument Gets Close-up on Mars Rocks

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News release: 2011-059 Feb. 18, 2011

Priscilla Vega (818) 354-1357
Jet Propulsion Laboratory, Pasadena, Calif.
Priscilla.r.vega@jpl.nasa.gov

Advanced NASA Instrument Gets Close-up on Mars Rocks

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-059&cid=release_2011-059

NASA's Mars Science Laboratory rover, Curiosity, will carry a next generation,
onboard "chemical element reader" to measure the chemical ingredients in Martian
rocks and soil. The instrument is one of 10 that will help the rover in its upcoming
mission to determine the past and present habitability of a specific area on the Red
Planet. Launch is scheduled between Nov. 25 and Dec. 18, 2011, with landing in August
2012.

The Alpha Particle X-Ray Spectrometer (APXS) instrument, designed by physics
professor Ralf Gellert of the University of Guelph in Ontario, Canada, uses the power of
alpha particles, or helium nuclei, and X-rays to bombard a target, causing the target to
give off its own characteristic alpha particles and X-ray radiation. This radiation is
"read by" an X-ray detector inside the sensor head, which reveals which elements and
how much of each are in the rock or soil.

Identifying the elemental composition of lighter elements such as sodium, magnesium
or aluminum, as well as heavier elements like iron, nickel or zinc, will help scientists
identify the building blocks of the Martian crust. By comparing these findings with
those of previous Mars rover findings, scientists can determine if any weathering has
taken place since the rock formed ages ago.

All NASA Mars rovers have carried a similar instrument – Pathfinder's rover
Sojourner, Spirit and Opportunity, and now Curiosity, too. Improvements have been
made with each generation, but the basic design of the instrument has remained the
same.

"APXS was modified for Mars Science Laboratory to be faster so it could make quicker
measurements. On the Mars Exploration Rovers [Spirit and Opportunity] it took us five
to 10 hours to get information that we will now collect in two to three hours," said
Gellert, the intrument's principal investigator. "We hope this will help us to investigate
more samples."

Another significant change to the next-generation APXS is the cooling system on the X-
ray detector chip. The instruments used on Spirit and Opportunity were able to take
measurements only at night. But the new cooling system will allow the instrument on
Curiosity to take measurements during the day, too.

The main electronics portion of the tissue-box-sized instrument lives in the rover's
body, while the sensor head, the size of a soft drink can, is mounted on the robotic
arm. With the help of Curiosity's remote sensing instruments – the Chemistry and
Camera (ChemCam) instrument and the Mastcam – the rover team will decide where
to drive Curiosity for a closer look with the instruments, including APXS.
Measurements are taken with the APXS by deploying the sensor head to make direct
contact with the desired sample.

The rover's brush will be used to remove dust from rocks to prepare them for
inspection by APXS and by MAHLI, the rover's arm-mounted, close-up camera.
Whenever promising samples are found, the rover will then use its drill to extract a
few grains and feed them into the rover's analytical instruments, SAM and CheMin,
which will then make very detailed mineralogical and other investigations.

Scientists will use information from APXS and the other instruments to find the
interesting spots and to figure out the present and past environmental conditions that
are preserved in the rocks and soils.

"The rovers have answered a lot of questions, but they've also opened up new
questions," said Gellert. "Curiosity was designed to pick up where Spirit and
Opportunity left off."

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars
Science Laboratory mission for the NASA Science Mission Directorate, Washington.

For more information about the mission, visit http://mars.jpl.nasa.gov/msl/ . To watch
the spacecraft being assembled and tested, visit http://www.ustream.tv/nasajpl .

-end-

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