Of the orbiter's three research modes (global monitoring, regional survey and targeted observations), this instrument's role will be in the targeted-observation mode. Researchers will use the high-resolution camera to examine shapes of deposits and other landforms produced by geologic and climatic processes. As one example, they will look for boulders in what appear to be flood channels, which would be evidence that the channels were cut by great flows of water, rather than glaciers or lava flows. And they will check the scale of layering in polar deposits. Those layers are believed to result from cyclical variations in Mars' climate; their thickness could be an indication of the time scale of climate cycles. Some layers are at least as thin as the current limit of resolution in orbital images, so higher-resolution imaging will add more information for deciphering climate history. Other anticipated targets include gullies, dunes and patterned ground.

This camera has a primary mirror diameter of 50 centimeters (20 inches) and a field of view of 1.15 degrees. At its focal plane, the instrument holds an array of 14 electronic detectors, each covered by a filter in one of three wavelength bands: 400 to 600 nanometers (blue-green), 550 to 850 nanometers (red), or 800 to 1000 nanometers (near infrared). Ten red detectors are positioned in a line totaling 20,028 pixels across to cover the whole width of the field of view. Two each of the blue-green and nearinfrared detectors lie across the central 20 percent of the field. Pixel size in images taken from an altitude of 300 kilometers (186 miles) will be 30 centimeters (12 inches) across, about a factor of two better than the highest-resolution down-track imaging possible from any earlier Mars orbiter and a factor of five better than any extended imaging to date. As a rule of thumb, at least three pixels are needed to show the shape of a feature, so the smallest resolvable features in the images will be about a meter (3 feet) across for an object with reasonable contrast to its surroundings. The instrument uses a technology called time delay integration to accomplish a high signal-to-noise ratio for unprecedented image quality.

Dr. Alfred McEwen of the University of Arizona, Tucson, is the principal investigator for the High Resolution Imaging Science Experiment. Ball Aerospace, Boulder, Colo., built the instrument for the university to provide to the mission.

The imaging spectrometer will work both in targeted and survey modes. It will target a few thousand selected areas for inspection at highest spatial resolution -- 18 meters (60 feet) per pixel -- and spectral resolution -- 544 different wavelengths. It will spend more of its time surveying the entire planet at resolutions of 100 to 200 meters (330 to 660 feet) per pixel in and about 70 different spectral channels ("colors"). The survey will find candidate sites for targeted inspection. The search for water-related minerals such as carbonates, clays and salts gets top priority for use of this instrument. Researchers are planning observations of sites such as smooth interiors of ancient craters that may have held lakes and volcanic regions that may have produced hot springs. They will also use the spectrometer to monitor seasonal changes in dust and ice particles suspended in the atmosphere.

The spectrometer has a telescope with a 10-centimeter (4-inch) aperture and a 2- degree field of view. That field of view produces images of swaths of Mars' surface about 10 kilometers (6 miles) wide. The instrument records the intensities of light in a range of wavelengths from 370 nanometers (violet) to 3,940 nanometers (near infrared) and divides that range into bands as small as 6.55 nanometers wide. It is mounted on a gimbal, which allows it to follow a target on the surface as the orbiter passes overhead.

The principal investigator for the Compact Reconnaissance Imaging Spectrometer for Mars is Dr. Scott Murchie of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md., which provided the instrument.

This instrument will perform roles in both the regional-survey and the targeted-observation modes. For the targeted mode, it will provide broad yet detailed visual context for interpreting observations by co-targeted instruments. Over the course of the primary science mission, it will produce regional surveys of about 15 percent of the planet's surface in relatively high resolution, which is expected to identify many targets for more detailed inspection. However, its ability to provide extended area imaging at moderately high resolution will enable it to examine the stratigraphy and morphology of many regional features and thus directly address key questions about changes in the Martian surface over geologic time and the roles that water and wind have played in these changes.

The camera is monochromatic and will produce black-and-white images. It has a single passband for visible light at 500 to 700 nanometers). It has a 5.8-degree field of view recorded onto a linear array 5,000 pixels wide, providing a resolution of 6 meters (20 feet) per pixel.

Malin Space Science Systems, San Diego, Calif., provided the Context Camera for this mission. Dr. Michael Malin is team leader for use of the instrument.

As a key instrument for the mission's global-monitoring mode, Mars Color Imager will provide daily weather maps of the entire planet and will track surface changes, such as the seasonal growing and shrinking of polar frosts and the movement of dust at other latitudes. Use of color filters will also enable researchers to identify the composition of clouds, which may be water ice, carbon-dioxide ice, or dust. Researchers will make use of the camera's ultraviolet filters to examine variations in the amount of ozone in the atmosphere. Ozone serves as a reverse indicator about water in Mars' atmosphere. Where there's more water, there's less ozone, and vice versa.

Mars Color Imager is essentially a copy of a camera that flew on the lost Mars Climate Orbiter mission. However the instrument on Mars Reconnaissance Orbiter has a wider fisheye lens to compensate for planned spacecraft rolls needed to target specific sites on Mars with other instruments. The camera has a field of view of 180 degrees. Its seven filters include five centered in visible-light wavelengths (425, 550, 600, 650 and 725 nanometers) and two in ultraviolet wavelengths (250 and 320 nanometers).

Malin Space Science Systems, San Diego, Calif., provided this instrument, and Dr. Michael Malin of that company is the principal investigator for it.

Mars Climate Sounder is one of the instruments serving the mission's global-monitoring research mode. One goal for researchers using it is to examine how solar energy interacts with the atmosphere and the surface. The measurements will also serve understanding of how the atmosphere moves water around the planet seasonally and the give and take between the surface and the atmosphere in quantities of water and dust. One area of regional focus is the polar regions, where measurements of the amount of solar energy absorbed by the surface ice can be used to estimate the amount of carbon dioxide that is exchanged between the atmosphere and the surface during the Martian year.

The Mars Climate Sounder instrument will address the scientific goals of an earlier, much heavier instrument that flew on the ill-fated Mars Observer and Mars Climate Orbiter spacecraft. It uses a pair of telescopes with apertures of 4 centimeters (1.6 inches). They are mounted in a cylinder in a yoke frame articulated so that, without repositioning the spacecraft, the telescopes can point sideways to the horizon and to space, down onto the planet, or at calibration targets attached to the yoke. Detectors record the intensity of radiation in nine channels or bands of the electromagnetic spectrum. One channel covers visible and near-infrared frequencies from 300 to 3,000 nanometers (0.3 to 3 microns). The other eight channels are in the thermal infrared part of the spectrum, from 12 to 50 microns.

Principal investigator for the Mars Climate Sounder is Dr. Daniel McCleese of NASA's Jet Propulsion Laboratory, Pasadena, Calif., and JPL provided the instrument to the mission.

The Shallow Subsurface Radar is a regional-survey instrument. Researchers will use it to follow up on the discovery by Mars Odyssey that the top layer of ground in many parts of Mars holds substantial quantities of hydrogen, believed to be in the form of water ice. The Odyssey instruments provided information about the top meter (3 feet) of ground. This radar will allow scientists to determine whether the ice-bearing material extends much deeper, helping scientists discern whether the ice content results from an equilibrium with the Martian atmosphere of today or persists as a remnant of a much thicker ice layer formed long ago. The instrument can distinguish icy layers from water-bearing layers. If the instrument does find any underground water, those sites could become landing-site candidates for future Mars rovers or human exploration. Researchers also plan to use the Shallow Radar for mapping the distribution of buried channels, studying the internal structure of Mars' ice caps, checking for liquid water underneath the ice caps, and examining the extent and relative depths of rock layers in selected regions. The structure of the upper crust may be very complex and so the use of surface observations may be critical to the proper interpretation of the radar data. Thus, areas like the Meridiani Planum region surrounding the rover Opportunity's research area are high-priority targets for radar mapping to see how far the surface layers with their water-related minerals extend laterally beneath the surface.

The instrument will transmit "chirps" lasting 85 milliseconds each at radio frequencies from 15 megahertz to 25 megahertz (wavelengths of about 15 meters or 50 feet in free space) with 10 watts of power. In most cases, it will operate on the night side of the planet. Compared with the only other ground-penetrating radar instrument ever to orbit Mars, the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the European Space Agency's Mars Express, the instrument on Mars Reconnaissance Orbiter will focus on shallower layers and have higher resolution. The Shallow Subsurface Radar's antenna will extend five meters (16 feet) to each side of the spacecraft. It is stowed in a folded-up configuration for launch and will not be deployed until after aerobraking has been completed. During the mission's two-year primary science phase, investigations with the Shallow Subsurface Rader are expected to return more data than the entire NASA Magellan mission, which mapped 99 percent of the surface of Venus with an orbiting radar instrument in the early 1990s.

The Italian Space Agency (ASI) selected Alenia Spazio, Rome, as the prime contractor for the Shallow Subsurface Radar and selected Dr. Roberto Seu of the University of Rome La Sapienza as the principal investigator for the instrument's science team. The Italian Space Agency provided the Shallow Subsurface Radar to NASA as a facility science instrument, with Dr. Seu as team leader. As part of this international collaboration, NASA selected a team of U.S. co-investigators, led by Dr. Roger Phillips of Washington University, St. Louis, to support Dr. Seu's team.

Two additional facility science investigations will use spacecraft subsystems to conduct scientific investigations of Mars.

Researchers will use the gravity measurements to study the processes that led to formation of surface features. They expect to study the thinning of the crust beneath the Valles Marineris rift zone, to map how volcanic material accumulated beneath the largest volcanoes and to see how impact structures modified the early Martian crust. They also anticipate that the data will reveal tiny changes in mass distribution as carbon dioxide moves from the surface to the atmosphere and back again. (In its frozen form, carbon dioxide is known as dry ice.) From changes in mass revealed by the gravitational effect on the spacecraft, scientists expect to measure how much dry-ice snow falls at high latitudes in the winter. These measurements will contribute to understanding the weather and climate on Mars.

Team leader for this investigation is Dr. Maria Zuber of the Massachusetts Institute of Technology, Cambridge, and NASA's Goddard Space Flight Center, Greenbelt, Md.

From the vertical structure of atmospheric density, scientists can determine atmospheric temperature and pressure. These may be clues to the fate of the water that was clearly on the Mars surface billions of years ago. One possibility is that water molecules are broken up by solar radiation into atomic hydrogen and oxygen, with the hydrogen escaping into outer space; another possibility is that some of the water is underground. The Atmospheric Structure Investigation will address the first possibility, loss of water via the escape of hydrogen to outer space. If the upper atmosphere is warm enough, some of the hydrogen atoms would have enough energy to escape the planet. Determining the density and temperature of the atmosphere will improve estimates of this loss process.

Other information about Mars atmosphere could also come from this investigation, just as discoveries resulted from the team's similar accelerometer measurements during aerobraking phases of the earlier Mars Global Surveyor and Mars Odyssey missions. The Global Surveyor investigation determined that even intermediate-size dust storms in the southern hemisphere immediately produced threefold increases of density in the northern hemisphere at aerobraking altitudes. These increases could have put the mission at risk if the spacecraft had not been raised to a higher altitude. The team also discovered enormous planetary-scale waves in density, which could also put the spacecraft at risk. Investigators developed techniques to predict when the spacecraft would fly through the peaks and valleys of these waves to establish safe aerobraking altitudes. During Odyssey's aerobraking, the team discovered "winter polar warming" near the north pole of Mars at high altitudes. North polar Martian winter atmospheric temperatures were warmer than expected by about 100 degrees Kelvin (180 degrees Fahrenheit). Mars Reconnaissance Orbiter's Atmospheric Structure investigators will search for similar winter warming near the south pole.

A new electronics design by Honeywell is expected to improve the signal-to-noise ratio of the Mars Reconnaissance Orbiter's accelerometers by more than a factor of 100 over the accelerometers on Mars Odyssey. This should allow measurements to be made at much higher altitudes than in the past, substantially improving estimates of the environment where hydrogen may escape. The investigation should also establish the nature of atmospheric changes due to variations in altitude, latitude, season, time-of-day, Mars-Sun distance, meteorological activity, dust storm activity, and solar activity.

Dr. Gerald Keating of George Washington University, Washington, is the team leader for this investigation.