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Space Topics: Mars Exploration Rovers
Science Instruments
Spirit and Opportunity, which were designed and built at the Jet Propulsion Laboratory (JPL), carry identical suites of five primary scientific instruments, known collectively as Athena science packages. The suites include: a panoramic camera (PanCam), a microscopic imager for close-ups, and three spectrometers. These instruments are augmented by a rock abrasion tool to scrape and drill into rock surfaces and magnetic targets to catch samples of Martian dust for examination. The spectrometers, microscopic imager, and rock abrasion tool share a turret at the end of a robotic arm.
In addition, each rover features supplemental tools primarily designed for engineering purposes but which have also been providing geologic information, including navigation cameras, a wider-angle stereo camera positioned on the same mast as the PanCam; and hazard avoidance cameras that ride low on the front and rear of the rover in stereo pairs to produce 3-D information about the nearby terrain. The rovers' wheels, in addition to moving the rovers along the terrain, have also been used as tools to dig or scuff up shallow trenches to better evaluate soil properties.
Cameras
Panoramic Camera (PanCam) is high-resolution, stereo camera developed at the Jet Propulsion Laboratory, and mounted at the top of each Mars Exploration Rover's mast along with the navigation cameras (NavCam). These stereo cameras take high-resolution, color images of the surface and surroundings, helping the MER team select rock and soil targets for intensive examination and to pick new regions for each rover to explore. PanCam images have been used to create captivating 3-D, 360-degree panoramas of the rovers' different locations. The PanCam boasts 14 different types of filters, allowing not only for full color images but also of spectral analyses of minerals and the atmosphere. This camera is also used to capture images of the Sun to determine each rover's exact position and orientation.
Microscopic Imager (MI) is a camera, developed at the Jet Propulsion Laboratory, which allows each rover to take very close-up images of the surface of rocks or soils and specifically to take black-and-white pictures of features as small as 1/10 of a millimeter across. These images can provide essential clues to how those rocks and soils were formed. Some of the targets the rovers study will be left in their natural state, but Spirit and Opportunity have used their MIs to take images of surfaces freshly exposed with their rock abrasion tools (RATs).
Engineering cameras
Navigation camera (NavCam) is a stereo camera system that takes black-and-white stereoscopic images with a broad field of view, supplying mission scientists with the information they need to choose a safe path for the rover to traverse among potentially hazardous rocks. The camera bar that contains the stereo NavCam, which is mounted in pairs at the top of the rover masts with the PanCam, can rotate a complete 360° horizontally and can swing up and down a complete 180° vertically.
Hazard camera (HazCam) is a pair of stereo camera systems designed to image the ground in the immediate vicinity of Spirit and Opportunity to safeguard against the rovers getting lost or inadvertently crashing into unexpected obstacles. Mounted in pairs both in front of and behind the rovers, this camera system works in tandem with onboard software, allowing the rovers to make intelligent choices about navigating around hazards.
Although intended primarily for navigation and safety, the navigation camera (NavCam) and hazard camera (HazCam) have produced images that have been used for science purposes.
Spectrometers
Miniature Thermal Emission Spectrometer (Mini-TES) records the thermal spectra of various rocks and soils to determine the types and amounts of minerals they contain. All warm objects emit heat, but different objects emit heat differently and the differences provide signatures of sorts by which scientists can identify them. One particular goal for the mini-TES has been to search for minerals that were formed by the action of water, such as carbonates and clays, or hematite. The mini-TES instrument has the same basic design, and was developed by the same team at Arizona State University, as the Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft.
Mössbauer spectrometer is an instrument specifically designed to study minerals that contain iron, which are common on the Martian surface. Developed by a team from the Johannes Gutenberg University in Mainz, Germany, this instrument has determined the composition and abundance of iron-bearing minerals to a high degree of accuracy. Although one Mössbauer measurement takes about 12 hours on average, the device has its own microcontroller, so measurements are often performed at night while the rover is “asleep.” Because Mössbauer spectra vary dramatically with changing temperature, measurements have been performed over a range of temperatures spanning both the daytime highs and the nighttime lows.
Alpha Particle X-Ray Spectrometer (APXS) is a spectrometer that detects alpha particles and x-rays emitted by rocks and soils in order to detect the amount of each chemical element they contain. The information from this instrument, which was produced by a team from the Max Planck Institute for Chemistry in Mainz, Germany, complements the detection of mineral composition by the Mössbauer spectrometer and Mini-TES to help scientists determine the origin and history of rocks and soils. One complete APXS measurement takes about 10 hours and has often been done at night, although taking X-ray measurements alone only requires a few hours.
Other instruments
Rock Abrasion Tool (RAT) is basically a grinding tool and drilling device that can create a hole 45 millimeters in diameter and 5 millimeters or deeper into a rock on the Martian surface. A rotating brush within the RAT sweeps dust away from the hole.
Rocks sitting on the Martian surface have been exposed to the action of wind, radiation, and dust for millions of years, so the interior of a rock may look very different from its exterior, and it may hold inside important clues to the regions history. Once a fresh surface has been exposed, the rover's other science instruments -- the microscopic imager, Mössbauer spectrometer, and the APXS – have examined the abraded area in detail.
Magnet Array is a group of magnets mounted on the front of each rover, on the rover deck, and inside the rock abrasion tool that are used to gather magnetic particles that are examined with the rover's cameras and spectrometers. Since magnetic minerals carried in dust could have formed in watery environments, scientists are interested in the composition of Martian dust.
A MarsDial (a Martian sundial) is carried by each rover as a calibration target, to determine accurate colors, brightness, and other information collected by the instruments. The MarsDial target features three gray regions and four colored regions, as well as a vertical post that cast a shadow across part of all three gray regions at some time between 10:00 a.m. and 2:00 p.m. (local Mars time) every day. The PanCam has been imaging the MarsDial nearly every day to show the amount of dust that is accumulated or blown off during windy days.
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