The Curiosity rover has ambitious science goals. Ambitious science goals necessitate ambitious science instruments. The science instruments onboard Curiosity are highly capable, state-of-the-art tools meant to aid Curiosity in its characterization of the geology, atmosphere, and environmental conditions on Mars, as well as its identification of potential biosignatures. Curiosity’s suite of science instruments include three cameras, four spectrometers, two radiation detectors, one environmental sensor, and one atmospheric sensor.
The cameras onboard the Curiosity rover are the mission scientists’ “eyes” on Mars. Without them, mission scientists would be blind. Cameras show us where the rover is, where it is going, and where it has been. They are necessary to navigate the rover’s trek along the surface, helping determine which sites to visit along the way.
Knowing the location of loose debris, boulders, cliffs, and other features will be important for planning the routes Curiosity will take after landing on Mars. Seen in Figure 1, the Mars Descent Imager (MARDI) took color video, a first for Mars exploration, during the rover's descent toward the surface. As soon as the rover released its heatshield, the Mars Descent Imager began producing a five-frames-per-second video stream of high-resolution, overhead views of the landing site. It continued acquiring images until the rover landed, at which time it turned off. The data was be stored onboard until it was sent to Earth, after the rover landed. A video of the landing imags can be seen here. In addition to helping mission planners select the best path of exploration, the MARDI will provide information about the larger geologic context surrounding the landing site. It also enabled the mission team to pinpoint the spacecraft's location after landing.
Figure 1. The Mars Descent Imager provided color video footage of the landing site and the surrounding terrain during the Mars Science Laboratory's descent to the surface of the red planet. Credit: NASA/JPL/Malin Space Science Systems
The Mast Camera, or Mastcam for short, takes color images and color video footage of the Martian terrain. The Mastcam consists of two camera systems (Figure 2) mounted on a mast extending upward from the Curiosity rover’s body. The Mastcam is being used to study the Martian landscape, rocks, and soils; to view frost and weather phenomena; and to support the driving and sampling operations of the rover.
Figure 2. Mastcam is made up of both the Mastcam 100 (left) and Mastcam 34 (right) cameras. Mastcam 100, offers telephoto capability while the other, Mastcam 34, offers a wider-angle view. Each provide color images and high-definition video, and they can be combined for stereo views. Credit: NASA/JPL/Malin Space Science Systems
To a human geologist, the hand lens is one the most important tools to have in the field. Small enough to be carried around the neck, a hand lens helps geologists identify minerals in rocks. The Mars Hand Lens Imager, or MAHLI (Figure 3), provides earthbound scientists with close-up views of the minerals, textures, and structures in Martian rocks and the surface layer of rocky debris and dust. Approximately four centimeters wide (1.5 inches), the camera takes color images of features as small as 12.5 micrometers, smaller than the width of a human hair. MAHLI carries white light sources, similar to the light from a flashlight, and ultraviolet light sources, similar to the light from a tanning lamp. This allows MAHLI to function during the day and night.
Figure 3. MAHLI provides close-up views of microbial-size features in rocks and soil. Credit: NASA/JPL-Caltech/Malin Space Science Systems
If cameras are Curiosity’s eyes, the onboard spectrometers make up the rover’s nose. The spectrometers “sniff out” the chemical composition of rocks and soil in Curiosity’s landing region.
The Alpha Particle X-Ray Spectrometer (Figure 4) measures the abundance of chemical elements in rocks and soils. The APXS is placed in contact with rock and soil samples on Mars and exposes the samples to alpha particles and X-rays. X-rays are a type of electromagnetic radiation, like light and microwaves. Alpha particles are helium nuclei, consisting of two protons and two neutrons. When alpha particles interact with atoms on the surfaces of samples, they excite electrons, releasing X-rays that can be measured with detectors. The energies of X-ray allow scientists to identify the important rock-forming elements. The APXS takes measurements both day and night. Its sensor head is designed to be smaller than a soda can and contains a highly sensitive X-ray detector. Most APXS measurements take two to three hours to reveal all elements present, but shorter analyses can also be made. Scientists use the APXS to help characterize and select rock and soil samples and then examine the interiors of the rocks following brushing by the Dirt Removal Tool on Curiosity’s robotic arm.
Figure 4. Curiosity’s Alpha Proton X-Ray Spectrometer (a) and electronics box (b). The ruler in the foreground is for scale. Credit: Canadian Space Agency/Univ. of Guelph
The Chemistry and Mineralogy instrument, or CheMin for short (Figure 5), identifies and measures the abundances of various minerals on Mars. To prepare rock samples for analysis, Curiosity drills into rocks, collects the resulting fine powder and delivers it to a sample holder. It also uses a scoop for collecting soil. CheMin then directs a beam of X-rays as fine as a human hair through the powdered material. When the X-ray beam interacts with the rock or soil sample, some of the X-rays are scattered by the regular patterns of atoms in the crystals. The angles at which the x-rays are scattered indicate the properties of the crystals, so that the minerals can be identified. In some cases, x-rays re-emitted at energies characteristic of the atoms present in the sample will also be detected, helping to determine the chemical composition of the sample as well as mineralogy. Different minerals are linked to certain kinds of environments. Scientists are using CheMin to search for mineral clues indicative of a past Martian environment that might have supported life.
Figure 5. Chemistry & Mineralogy (CheMin) X-Ray Diffraction Instrument. Designed to be about the size of a laptop computer inside a carrying case, the Chemistry and Mineralogy Instrument identifies and measures the abundances of minerals on Mars. A rotating wheel in the center of the rectangular housing carries individual rock and soil samples for chemical analysis. Credit: NASA/JPL-Caltech
The Sample Analysis at Mars instrument suite (Figure 6) takes up more than half the science payload on board Curiosity and features chemical equipment found in many scientific laboratories on Earth. SAM searches for compounds of the element carbon, including methane, which are associated with life and explores ways in which they are generated and destroyed in the Martian atmosphere. SAM is in reality a combination of three instruments: 1) a mass spectrometer, which identifies chemical elements in the samples by their mass, 2) a gas chromatograph, which heats soil and rock samples until they vaporize, and then separate the resulting gases into various components for analysis, and 3) a tunable laser spectrometer, which measures the abundance of various isotopes (isotopes are atoms of the same element having the same number of protons but a different number of neutrons) of carbon, hydrogen, and oxygen in atmospheric gases such as methane, water vapor, and carbon dioxide. SAM will hunts for and measures the abundances of other light elements, such as hydrogen, oxygen, and nitrogen, associated with life.
Figure 6. The Sample Analysis at Mars instrument. The SAM instrument suite weighs about 83 pounds (38 kilograms) and makes up about half the science payload of Curiosity. It is a suite of three instruments that will search for carbon-based compounds associated with life. Credit: NASA/GSFC
The Radiation Assessment Detector (RAD) is one of the first instruments sent to Mars specifically to prepare for future human exploration. The size of a small toaster or six-pack of soda, RAD (Figure 7) measures and identifies all high-energy radiation on the Martian surface such as protons, energetic ions of various elements, neutrons, and gamma rays. This includes not only direct radiation from space, but also secondary radiation produced by the interaction of space radiation with the Martian atmosphere and surface rocks and soils. To help prepare for future human exploration, RAD is collecting data that will allow scientists to determine the effect radiation would have on astronauts based on how much radiation they would be exposed on the surface of Mars. A stack of paper-thin, silicon detectors and a small block of cesium iodide measure high-energy charged particles that encounter RAD after coming through the Martian atmosphere. Combined, these materials will slow down the incoming particles. RAD can determine the type of particle by the amount they are slowed by these materials.
Figure 7. About the size of a small toaster, the Radiation Assessment Detector looks skyward and uses a stack of silicon detectors and a crystal of cesium iodide to measure galactic cosmic rays and solar particles that pass through the Martian atmosphere. Credit: NASA/JPL-Caltech/SwRI
Scientists expect to find hydrogen on Mars in two places: locked in water ice and minerals that contain water. At the request of the Russian Federal Space Agency, Curiosity carries a pulsing neutron generator called the Dynamic Albedo of Neutrons (DAN) that is sensitive enough to detect very small concentrations of ice at the surface, as well as underground ice. DAN focuses a beam of neutrons on the Martian surface from the rover at a height of 79 centimeters (~31 inches) (Figure 8). The neutrons are expected to travel one to two meters (three to six feet) below the surface before being absorbed by hydrogen atoms in subsurface ice. If the beam of neutrons encounters a layer of ice beneath the surface, DAN will detect a relatively greater number of slower neutrons reflected at the surface. If there are no ice layers or water-bearing minerals beneath the surface, DAN will detect a relatively greater amount of faster neutrons reflected at the surface.
Figure 8. Water, whether liquid or frozen, absorbs neutrons more than other substances. The Detector of Albedo Neutrons on the Curiosity rover uses this characteristic to search for subsurface ice on Mars. Credit: NASA/JPL-Caltech/Russian Federal Space Agency
Environmental and Atmospheric Sensors
The Centro de Astrobiologia (CAB), a joint center of Consejo Superior de Investigaciones Cientificas - Instituto Nacional de Tecnica Aeroespacial (CSIC-INTA) in Spain, provided a weather monitoring station contributed by the Spanish government. The Rover Environmental Monitoring Station, or REMS (Figure 9), measures, and provides daily and seasonal reports on, atmospheric pressure, humidity, ultraviolet radiation at the Martian surface, wind speed and direction, air temperature, and ground temperature around the rover. Two small booms on the rover mast record wind speed to characterize air flow near the Martian surface from breezes, dust devils, and dust storms. A sensor inside the rover's electronic box is exposed to the atmosphere through a small opening and measures changes in air pressure. A suite of infrared sensors on one of the booms (Boom 1) measures the intensity of infrared radiation emitted by the ground, which provides an estimate of ground temperature. A sensor on the other boom (Boom 2) tracks atmospheric humidity. Both booms carry sensors for measuring air temperature. An array of detectors on the rover deck that are sensitive to specific frequencies of sunlight measure ultraviolet radiation at the Martian surface and correlate it with other changes in the environment.
Figure 9. The Rover Environmental Monitoring Station monitors atmospheric pressure, humidity, wind currents, and ultraviolet radiation from the sun. Image credit: NASA/JPL-Caltech/INTA (Instituto Nacional de Tecnica Aeroespacial)
The Mars Science Laboratory Entry, Descent, and Landing Instrument (MEDLI) collected engineering data during the spacecraft's high-speed, extremely hot entry into the Martian atmosphere. MEDLI data is invaluable to engineers as they design future Mars missions. The data helps them design systems for entry into the Martian atmosphere that are safer, more reliable, and lighter weight. MEDLI is made up of two different instruments: the MISP (MEDLI Integrated Sensor Plugs) and MEADS (Mars Entry Atmospheric Data System). While the spacecraft faced extreme heat during entry into the Martian atmosphere, MISP measured how hot it gets at different depths in the spacecraft's heat-shield material. Predicted heating levels are about three times higher than those of the Space Shuttle when it enters Earth's atmosphere. MEADS measured the atmospheric pressure on the heat shield at the seven MEADS locations during entry and descent through Mars' atmosphere. The MEADS pressure sensors are arranged in a special cross pattern. This cross pattern will allow engineers to determine the spacecraft's orientation (its position and how that changes) as a function of time.