NASA's next Mars rover, Curiosity, will wield an arm-mounted magnifying  camera similar to one on the Mars Rover Opportunity, which promptly  demonstrated its importance for reading environmental history from rocks  at its landing site in 2004.
Within a few weeks after the landing, that camera at the end of  Opportunity's arm revealed details of small spheres embedded in the  rocks, hollows where crystals had dissolved, and fine layering shaped  like smiles. These details all provided information about the site's wet  past.
The camera installed on the end of Curiosity's arm this month is the  Mars Hand Lens Imager, or MAHLI. Its work will include the same type of  close-up inspections accomplished by the comparable camera on  Opportunity, but MAHLI has significantly greater capabilities:  full-color photography, adjustable focus, lights, and even video. Also,  it sits on a longer arm, one that can hold MAHLI up higher than the  cameras on the rover's mast.  MAHLI will use those capabilities as one  of 10 science instruments to study the area of Mars where NASA's Mars  Science Laboratory mission lands Curiosity in August 2012.
The Mars Hand Lens Imager takes its name from the magnifying tool  that every field geologist carries. Ken Edgett of Malin Space Science  Systems, San Diego, is the principal investigator for the instrument.   He said, "When you’re out in the field and you want to get a quick idea  what minerals are in a rock, you pick up the rock in one hand and hold  your hand lens in the other hand. You look through the lens at the  colors, the crystals, the cleavage planes: features that help you  diagnose what minerals you see.
"If it's a sedimentary rock, such as the sandstone you see at Arches  National Park in Utah, or shale -- which is basically petrified mud --  like in the Painted Desert in Arizona, you use the hand lens not just to  see what minerals are in it but also the sizes and shapes of the grains  in the rock. You also look at the fine-scale layering in the rock to  get an idea of the sequence of events. Sedimentary rocks record past  events and environments."
While other instruments on Curiosity will provide more information  about what minerals are in rocks, the Mars Hand Lens Imager will play an  important role in reading the environmental history recorded in  sedimentary rocks. The mission's science team will use the instruments  to assess whether the selected landing area has had environmental  conditions favorable for life and for preserving evidence about whether  life existed.
The team currently assembling and testing Curiosity and other parts  of the Mars Science Laboratory spacecraft at NASA's Jet Propulsion  Laboratory, Pasadena, Calif., is continuing tests of MAHLI this month,  now that the camera is mounted beside other tools on the robotic arm.  The spacecraft will launch from Florida between Nov. 25 and Dec. 18,  2011.
Edgett led the preparation in early 2004 of a proposal to include  MAHLI in the Mars Science Laboratory's payload. During those same  months, the camera on Opportunity's arm -- that mission's Microscopic  Imager -- was demonstrating the potential value of a successor, and  generating ideas for improvements. Opportunity's Microscopic Imager has a  fixed focus. To get targets in focus, it always needs to be placed the  same distance from the target, recording a view of an area 3 centimeters  (1.2 inches) across. To view a larger area, the camera takes multiple  images, sometimes more than a dozen, each requiring a repositioning of  Opportunity's arm.
"When I was writing the proposal, the Microscopic Imager took about  40 images for a mosaic of one rock," Edgett said. "That's where the idea  came from to make the focus adjustable. With adjustable focus, the  science team has more flexibility for trade-offs among the rover's  resources, such as power, time, data storage and data downlink. For  example, the camera could take one or two images from farther away to  cover a larger area, then go in and sample selected parts in higher  resolution from closer up."
MAHLI can focus on targets as close as about 21 millimeters (0.8  inch) and as distant as the horizon or farther.  JPL's Ashwin Vasavada,  deputy project scientist for the Mars Science Laboratory, said, "MAHLI  is really a fully functional camera that happens to be on the end of the  arm. The close-up capability is its specialty, but it will also be able  to take images or videos from many viewpoints inaccessible to the  cameras on the mast, such as up high, down low, under the rover and on  the rover deck. Think of it like a hand-held camera with a macro lens,  one that you could use for taking pictures of the Grand Canyon, of  yourself, or of a bumblebee on a flower."
Edgett is looking forward to what the camera will reveal in rock  textures. "Just like larger rocks in a river, grains of sand carried in a  stream get rounded from bouncing around and colliding with each other,"  he said. "If you look at a sandstone with a hand lens and see rounded  grains, that tells you they came from a distance. If they are more  angular, they didn't come as far before they were deposited in the  sediment that became the rock. Where an impact excavated a crater,  particles of the material ejected from the crater would be very angular.
"When you're talking about ancient rocks as clues for assessing  habitability," he continued, "you're talking about the environments the  sediments were deposited in -- whether a lake, a desert, an ice field.  Also, what cemented the particles together to become rocks, and what  changes have affected the rock after the sediments were deposited? All  these things are relevant to whether an environment was favorable for  life and also whether it was favorable for preserving the record of that  life. Earth is a planet teeming with life, but most rocks have not  preserved ancient organisms; Mars will be even more challenging than  Earth in this sense."
Edgett says he is eager to see an additional image from this camera  besides the details of rock textures. With the arm extended upwards, the  camera can look down at the rover for a dramatic self-portrait on Mars.  But as for the most important image the Mars Hand Lens Imager will  take: "That will be something that surprises us, something we're not  expecting."
Mars Science Laboratory is managed by NASA’s Jet Propulsion  Laboratory, Pasadena, Calif.  JPL also manages the Mars Exploration  Rovers Spirit and Opportunity.  JPL is a division of the California  Institute of Technology in Pasadena.
  More information about NASA's Mars Science Laboratory is at:  
http://www.nasa.gov/msl .