NASA / JPL-Caltech
An artist's concept of Curiosity searching for interesting samples on Mars' surface.
updated 12/6/2011 5:46:48 PM ET 2011-12-06T22:46:48

The Mars Science Laboratory is on its way to the Red Planet, and its rover Curiosity should touch down next summer. If the mission hits pay dirt and comes across organic material, then one instrument in particular has the chemical tools for studying these building blocks of life.

The instrument is called Sample Analysis at Mars, or SAM (or "Samantha" to those who built her). As the name makes clear, SAM is there to analyze samples taken from the surface and from the atmosphere. It uses sophisticated chemical lab equipment packed into the size of a microwave oven.

SAM sits in the belly of the rover and will be fed solid samples by the robotic arm. It is one of 10 science instruments on Curiosity that all work together to study the past and present habitability of Mars.

"Life on Earth means water, energy and the complexity of carbon chemistry," says Paul Mahaffy from NASA Goddard Space Flight Center and the principle investigator of the SAM instrument. "We'll be looking for all of the above, but with a special emphasis on the complexity."

Curiosity's predecessors, the Mars Exploration Rovers Spirit and Opportunity, had a mantra of "follow the water."  Now, the paradigm is shifting toward "follow the carbon," Mahaffy says.

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SAM will have the sensitivity for measuring organic molecules at a level of a few parts per billion, but there's no guarantee that any organics will be found. A more sure-fire bet is that the mission will better characterize whether Mars was ever friendly to organic compounds and the life that depends on them.

Ten instruments in harmony
The Curiosity rover is expected to reach the Martian surface on Aug. 6, 2012. The chosen landing site is Gale Crater – a 100-mile-wide hole in the ground that likely accommodated an ancient lake long ago.

"We assume water was there in the past, but we'd like to find out how long did it last," Mahaffy says.

In the middle of the crater is a 3-mile-high mound that has sediment-layers that span a wide range of the planet's history. Curiosity plans to drive up the mound several hundred meters during its nominal mission of one Martian year (or roughly two Earth years). The strategy is to explore various rock layers that may have formed in both wet and dry environments.

The instruments will work in concert to locate the most promising sites. The Mast Camera (MastCam) will scope out the terrain from 2 meters above the surface. The adjacent ChemCam zaps rocks with an infrared laser and analyzes the ionized vapor that is released.

When this remote sensing identifies a small area of interest, the robotic arm descends to allow close-up investigation with the Alpha-Particle X-ray Spectrometer (APXS) and the Mars Hand Lens Imager (MAHLI).  The arm also has a drill, which can grind into a rock and collect the fine powder for delivery to SAM and its analysis partner called CheMin.

"We look at the data from the other instruments and decide whether a particular rock is really interesting enough to take a sample and 'ingest' it for CheMin and SAM analysis," Mahaffy says.

CheMin is an X-ray diffraction instrument that can identify mineral structure and composition. SAM complements CheMin by examining volatile gases that may be trapped in ancient rocks.

Rounding out the rover's suite of instruments are a subsurface water detector ( DAN ), a weather station (REMS), a radiation monitor (RAD) and a descent camera (MARDI).

NASA / JPL-Caltech
The Curiosity rover touches down on the Martian surface in this artist's rendition.

Do you smell what rocks I'm cooking?
The SAM package can perform several types of experiment, but the big headliner involves heating rock samples and looking for organics in the gases that are released.

In detail, a powder sample from the drill is dropped into a funnel and shaken into one of 74 sample cups. The sample manipulation system (SMS) moves the cup to an oven that ramps the temperature up to around 1,000 degrees Celsius. A portion of the released vapor enters the Quadrupole Mass Spectrometer (QMS), which identifies the main constituents through their charge-to-mass ratio.

The rest of the gas sample is sent through a highly-absorbent polymer that traps organic molecules. The trapped organics are then delivered to the Gas Chromatograph (GC), which is a set of six long columns that separate out the different molecular species. The final identification is done by the QMS, which can say, for example, how much of this or that amino acid or hydrocarbon is in the sample.

"Gas chromatography-mass spectrometry is one of the most common analytic techniques on Earth, and we are just taking it to Mars," Mahaffy says.

The challenge has been to package everything to fit within the space and energy constraints placed on the rover's instruments. The 30-meters-long GC columns, for instance, had to be wound up into tight spirals that saved space as well as "heating bills."

Tuning for isotopes
For precise chemical measurements, SAM includes a second spectrometer, called the Tunable Laser Spectrometer (TLS). The TLS is designed to detect only a few simple molecules, but it can distinguish the different isotope concentrations.

As an example, carbon dioxide trapped in a rock will contain both carbon-13 and carbon-12. The TLS will be able to measure this ratio and learn something about the atmospheric conditions at the time the rock formed. SAM will be able to compare this with current conditions, since it has inlets for sampling the atmosphere in the vicinity of the rover.

Another gas targeted by TLS is methane. This greenhouse gas is a hot topic right now because trace amounts of it have been recently detected on Mars from Earth-bound telescopes. Surprisingly, this methane appears to come and go on a seasonal basis.

The TLS instrument should be able to detect methane in the atmosphere at the levels previously observed. And since Curiosity will operate for a full Martian year, the team should also be able to verify if any seasonal variations are occurring.

The great organic hope
Mars is currently not a very friendly place for life's chemistry. Organic molecules can be destroyed by the unblocked UV light and cosmic rays, as well as oxidizing compounds in the atmosphere and soil.

But organics may be preserved in safe havens below the surface. Curiosity may be able to drill down and tap into these preservation environments, which gives it an advantage over previous organic-detection missions on the Viking and Phoenix landers that could only scratch the surface.

"We are also are not limited to one spot like Viking and Phoenix," Mahaffy says. The rover can drive around and search for the best rocks that might be hiding organics.

NASA / JPL-Caltech
Technicians and engineers carefully install the 88-pound (40-kilogram) SAM instrument on the Curiosity rover. The picture was taken at NASA's Jet Propulsion Laboratory, Pasadena, Calif., on Jan. 6.

Mahaffy and others do not want to oversell their chances.

"We don't expect to find a site rich in organics from ancient times," he says.

But if they did, then SAM could sort through the organics and begin measuring their isotopic abundances.  This could say whether this complexity came from abiotic processes or if life is somehow involved.

It's a big if, but that's what drives our curiosity.

This story was provided by Astrobiology Magazine, a web-based publication sponsored by the NASA astrobiology program.

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Explainer: 11 amazing things the Mars rover can do

  • The car-sized Curiosity rover is a 1-ton robotic beast that will take planetary exploration to the next level.

    Curiosity rover is the centerpiece of NASA's $2.5 billion Mars Science Laboratory. Its main goal is to assess whether the Red Planet is, or ever was, capable of supporting microbial life. The rover will employ 10 different science instruments to help it answer this question once it touches down on the Red Planet. Here's a brief rundown of these instruments (and one more on the rover's heat shield).

    — Mike Wall,

  • Mast Camera (MastCam)

    T.A. Dutch Slager / NASA / JPL-Caltech
    This view of the Curiosity rover's remote sensing mast shows the ChemCam in the white box at top, and the two cameras of the Mastcam system just below. Additional navigation cameras are placed farther outward from the Mastcam cameras.

    The MastCam is Curiosity's workhorse imaging tool. It will capture high-resolution color pictures and video of the Martian landscape, which scientists will study and laypeople will gawk at.

    MastCam consists of two camera systems mounted on a mast that rises above Curiosity's main body, so the instrument will have a good view of the Red Planet environment as the rover chugs through it. MastCam images will also help the mission team drive and operate Curiosity. (Photos of NASA's Curiosity Rover)

  • Mars Hand Lens Imager (MAHLI)

    NASA / JPL-Caltech
    The Curiosity rover's Mars Hand Lens Imager will acquire color close-up images of rocks and surface materials. A Swiss Army knife is shown for scale.

    MAHLI will function much like a high-powered magnifying glass, allowing Earthbound scientists to get up-close looks at Martian rocks and soil. The instrument will take color pictures of features as tiny as 12.5 microns — smaller than the width of a human hair.

    MAHLI sits on the end of Curiosity's five-jointed, 7-foot (2.1-meter) robotic arm, which is itself a marvel of engineering. So mission scientists will be able to point their high-tech hand lens pretty much wherever they want.

  • Mars Descent Imager (MARDI)

    NASA / JPL-Caltech / MSSS
    The Mars Descent Imager is flying on the Curiosity rover. A Swiss Army knife is included in the picture for purposes of showing scale.

    MARDI, a small camera located on Curiosity's main body, will record video of the rover's descent to the Martian surface (which will be accomplished with the help of a hovering, rocket-powered sky crane). (Video: Curiosity's Peculiar Landing)

    MARDI will click on a mile or two above the ground, as soon as Curiosity jettisons its heat shield. The instrument will then take video at five frames per second until the rover touches down. The footage will help the MSL team plan Curiosity's Red Planet rovings, and it should also provide information about the geological context of the landing site, the 100-mile-wide (160-km) Gale Crater.

  • Sample Analysis at Mars (SAM)

    NASA / JPL-Caltech
    This illustration of the mechanical configuration of the SAM shows the three instruments and several elements of the Chemical Separation and Processing Laboratory.

    SAM is the heart of Curiosity; at 83 pounds (38 kilograms), it makes up about half of the rover's science payload.

    SAM is actually a suite of three separate instruments — a mass spectrometer, a gas chromatograph and a laser spectrometer. These instruments will search for carbon-containing compounds, the building blocks of life as we know it. They will also look for other elements associated with life on Earth, such as hydrogen, oxygen and nitrogen.

    The SAM instrument suite is located in Curiosity's main body. The rover's robotic arm will drop samples into SAM via an inlet on the rover's exterior. Some of these samples will come from the interior of rocks, powder bored out by a 2-inch (5-centimeter) drill situated at the end of the arm.

    None of Curiosity's predecessors could get deep into Martian rocks, so scientists are excited about the drill.

    "For a geologist that studies rocks, there's nothing better than getting inside," said MSL deputy project scientist Joy Crisp, of NASA's Jet Propulsion Laboratory in Pasadena, Calif.

  • Chemistry and Mineralogy (CheMin)

    NASA / JPL-Caltech
    Clean-room workers carefully steer the hoisted CheMin instrument toward its installation into the Curiosity rover.

    CheMin will identify different types of minerals on Mars and quantify their abundance, which will help scientists better understand past environmental conditions on the Red Planet.

    Like SAM, CheMin has an inlet on Curiosity's exterior to accept samples delivered by the rover's robotic arm. The instrument will shine a fine X-ray beam through the sample, identifying minerals' crystalline structures based on how the X-rays diffract.

    "This is like magic to us," Crisp told X-ray diffraction is a leading diagnostic technique for Earthbound geologists, she explained, but it hasn't made it to Mars yet. So CheMin should help Curiosity provide more definitive mineral characterizations than previous Mars rovers such as Spirit and Opportunity have been able to achieve.

  • Chemistry and Camera (ChemCam)

    NASA / JPL-Caltech
    An artist's conception shows the Curiosity rover's ChemCam firing its laser at Martian rock.

    For sheer coolness, it's tough to beat ChemCam. This instrument will fire a laser at Martian rocks from up to 30 feet (9 meters) away and analyze the composition of the vaporized bits.

    ChemCam will thus enable Curiosity to study rocks that are out of reach of its flexible robotic arm. It will also help the mission team determine from afar whether or not they want to send the rover over to investigate a particular landform.

    ChemCam is composed of several different parts. The laser sits on Curiosity's mast, along with a camera and a small telescope. Three spectrographs sit in the rover's body, connected to the mast components by fiber optics. The spectrographs will analyze the light emitted by excited electrons in the vaporized rock samples.

  • Alpha Particle X-Ray Spectrometer (APXS)

    NASA / JPL-Caltech
    The sensor head for the Alpha Particle X-ray Spectrometer is installed during testing. The head is 7.8 centimeters or about 3 inches tall.

    APXS, which sits at the end of Curiosity's arm, will measure the abundances of various chemical elements in Martian rocks and dirt.

    Curiosity will place the instrument in contact with samples of interest, and APXS will shoot out X-rays and helium nuclei. This barrage will knock electrons in the sample out of their orbits, causing a release of X-rays. Scientists will be able to identify elements based on the characteristic energies of these emitted X-rays.

    Spirit and Opportunity were outfitted with a previous version of APXS and used the instrument to help elucidate the prominent role water has played in shaping the Martian landscape. (Latest Mars Photos From Spirit and Opportunity)

  • Dynamic Albedo of Neutrons (DAN)

    NASA / JPL-Caltech / Roscosmos
    This diagram shows how the Detector of Albedo Neutrons could be used to sense the presence of subsurface water on Mars.

    DAN, located near the back of Curiosity's main body, will help the rover search for ice and water-logged minerals beneath the Martian surface.

    The instrument will fire beams of neutrons at the ground, then note the speed at which these particles travel when they bounce back. Hydrogen atoms tend to slow neutrons down, so an abundance of sluggish neutrons would signal underground water or ice.

    DAN should be able to map out water concentrations as low as 0.1 percent at depths up to 6 feet (2 m).

  • Radiation Assessment Detector (RAD)

    NASA / JPL-Caltech
    The RAD instrument is mounted just below the Curiosity rover's top deck, with the charged particle telescope pointing toward the zenith.

    The toaster-size RAD is designed specifically to help prepare for future human exploration of Mars. The instrument will measure and identify high-energy radiation of all types on the Red Planet, from fast-moving protons to gamma rays.

    RAD's observations will allow scientists to determine just how much radiation an astronaut would be exposed to on Mars. This information could also help researchers understand how much of a hurdle Mars' radiation environment might have posed to the origin and evolution of life on the Red Planet.

  • Rover Environmental Monitoring Station (REMS)

    This diagram shows the location of the REMS booms on the rover's mast, plus detailed views showing the location of wind, humidity and temperature sensors.

    This tool, which sits partway up Curiosity's mast, is a Martian weather station. REMS will measure atmospheric pressure, humidity, wind speed and direction, air temperature, ground temperature and ultraviolet radiation.

    All of this information will be integrated into daily and seasonal reports, allowing scientists to get a detailed look at the Martian environment.

  • MSL Entry, Descent and Landing Instrumentation (MEDLI)

    Lockheed Martin
    The MEDLI instrument package is the black box in the middle left of this photo, which shows the heatshield for the Mars Science Laboratory.

    MEDLI isn't one of Curiosity's 10 instruments, since it was built into the heat shield that protected the rover during its descent through the Martian atmosphere. But it's worth a few words here.

    MEDLI measured the temperatures and pressures that the heat shield experienced as the MSL spacecraft streaked through the Martian sky. This information can tell engineers how well the heat shield, and their models of the spacecraft's trajectory, performed.

    Researchers will use MEDLI data to improve designs for future Mars-bound spacecraft.

    You can follow senior writer Mike Wall on Twitter: @michaeldwall. Follow for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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