Mars Exploration Rovers - Science Investigations
The Mars Exploration Rover mission seeks to determine the history of climate and
water at sites on Mars where conditions may once have been favorable to life. Each
rover is equipped with a suite of science instruments that will be used to read the geo-logic
record at each site, to investigate what role water played there, and to determine
how suitable the conditions would have been for life.
Based on priorities of the overall Mars Exploration Program, the following science
objectives were developed for Spirit and Opportunity:
- Search for and characterize a diversity of rocks and soils that hold clues to
past water activity (water-bearing minerals and minerals deposited by
precipitation, evaporation, sedimentary cementation, or hydrothermal activity).
- Investigate landing sites, selected on the basis of orbital remote sensing, that
have a high probability of containing physical and/or chemical evidence of the
action of liquid water.
- Determine the spatial distribution and composition of minerals, rocks and soils
surrounding the landing sites.
- Determine the nature of local surface geologic processes from surface
morphology and chemistry.
- Calibrate and validate orbital remote-sensing data and assess the amount
and scale of heterogeneity at each landing site.
- For iron-containing minerals, identify and quantify relative amounts of specific
mineral types that contain water or hydroxyls, or are indicators of formation by
an aqueous process, such as iron-bearing carbonates.
- Characterize the mineral assemblages and textures of different types of rocks
and soils and put them in geologic context.
- Extract clues from the geologic investigation, related to the environmental
conditions when liquid water was present and assess whether those
environments were conducive for life.
The package of science instruments on the rovers is collectively known as the Athena
science payload. Led by Dr. Steven Squyres, professor of astronomy at Cornell
University, Ithaca, N.Y., the Athena package was originally proposed to fly under differ-ent
Mars lander and rover mission concepts before being finalized as the science pay-load
for the Mars Exploration Rovers.
The package consists of two instruments designed to survey the landing site, as well
as three other instruments on an arm designed for closeup study of rocks. Also on the
arm is a tool that can scrape away the outer layers of rocks. Those instruments are
supplemented by magnets and calibration targets that will enable other studies.
The two instruments that will survey the general site are:
- Panoramic Camera will view the surface using two high-resolution color
stereo cameras to complement the rover's navigation cameras. Delivering
panoramas of the martian surface with unprecedented detail, the instrument's
narrow-angle optics provide angular resolution more than three times higher
than that of the Mars Pathfinder cameras. The camera's images will help
scientists decide what rocks and soils to analyze in detail, and will provide
information on surface features, the distribution and shape of nearby rocks, and
the presence of features carved by ancient waterways. The camera's two eyes
sit 30 centimeters (12 inches) apart, about 1.5 meters (5 feet) above ground
level on the rover's mast. The instrument carries 14 different types of filters,
allowing not only full-color images but also spectral analysis of minerals and the
atmosphere. Each exposure of each eye produces a digital image 1,028 pixels
wide by 1,028 pixels wide. Full-circle panoramas will be mosaics about 24
frames wide and four frames high, for a combined image full of fine detail even
if enlarged to the size of a giant movie screen.
- The Mini-Thermal Emission Spectrometer is an instrument that sees
infrared radiation emitted by objects. By measuring the brightness of that
emission in 167 different "colors" of infrared for each point it views, this
spectrometer will determine from afar the mineral composition of martian
surface features and allow scientists to select specific rocks and soils to
investigate in detail. Observing in the infrared allows scientists to see through
dust that coats many rocks, allowing the instrument to recognize carbonates,
silicates, organic molecules and minerals formed in water. Infrared data will also
help scientists assess the capacity of rocks and soils to hold heat over the wide
temperature range of a martian day. Besides studying rocks, the instrument will
be pointed upward to make the first-ever high-resolution temperature profiles
through the martian atmosphere's boundary layer. The data from the instrument
will be complement that obtained by the thermal emission spectrometer on the
Mars Global Surveyor orbiter. Most of the instrument rides inside the
rover. The rover's camera mast doubles as a periscope for this spectrometer,
and a scanning mirror assembly high on the mast reflects infrared light down
through the mast to the spectrometer.
The instruments on the rover arm are:
- The Microscopic Imager is a combination of a microscope and a camera. It
will produce extreme closeup black-and-white views (at a scale of hundreds of
microns) of rocks and soils examined by other instruments on the rover arm,
providing context for the interpretation of data about minerals and elements.
The imager will help characterize sedimentary rocks that formed in water, and
thus will help scientists understand past watery environments on Mars. This
instrument will also yield information on the small-scale features of rocks formed
by volcanic and impact activity as well as tiny veins of minerals like the
carbonates that may contain microfossils in the famous Mars meteorite,
ALH84001. The shape and size of particles in the martian soil can also be
determined by the instrument, which provides valuable clues about how the soil
- Because many of the most important minerals on Mars contain iron, the
Mössbauer Spectrometer is designed to determine with high accuracy the
composition and abundance of iron-bearing minerals that are difficult to detect
by other means. Identification of iron-bearing minerals will yield information
about early martian environmental conditions. The spectrometer is also capable
of examining the magnetic properties of surface materials and identifying
minerals formed in hot, watery environments that could preserve fossil evidence
of martian life. The instrument uses two pieces of radioactive cobalt-57, each
about the size of a pencil eraser, as radiation sources. The instrument is
provided by Germany.
- The Alpha Particle X-Ray Spectrometer will accurately determine the
elements that make up rocks and soils. This information will be used to
complement and constrain the analysis of minerals provided by the other
science instruments. Through the use of alpha particles and X-rays, the
instrument will determine a sample's abundances of all major rock-forming
elements except hydrogen. Analyzing the elemental make-up of martian surface
materials will provide scientists with information about crustal formation,
weathering processes and water activity on Mars. The instrument uses small
amounts of curium-244 for generating radiation. It is provided by Germany.
- The arm-mounted instruments will be aided by a Rock Abrasion Tool that
will act as the rover's equivalent of a geologist's rock hammer. Positioned
against a rock by the rover's instrument arm, the tool uses a grinding wheel to
remove dust and weathered rock, exposing fresh rock underneath. The tool will
expose an area 4.5 centimeters (2 inches) in diameter, and grind down to a
depth of as much as 5 millimeters (0.2 inch).
In addition, the rovers are equipped with the following that work in conjunction with sci-ence
- Each rover has three sets of Magnet Arrays that will collect airborne dust
for analysis by the science instruments. Mars is a dusty place, and some of that
dust is highly magnetic. Magnetic minerals carried in dust grains may be freeze-dried
remnants of the planet´s watery past. A periodic examination of these
particles and their patterns of accumulation on magnets of varying strength can
reveal clues about their mineralogy and the planet´s geologic history. One set
of magnets will be carried by the rock abrasion tool. As it grinds into martian
rocks, scientists will have the opportunity to study the properties of dust from
these outer rock surfaces. A second set of two magnets is mounted on the front
of the rover for the purpose of gathering airborne dust. These magnets will be
reachable for analysis by the Mössbauer and alpha particle X-ray
spectrometers. A third magnet is mounted on the top of the rover deck in view of
the panoramic camera. This magnet is strong enough to deflect the paths of
wind-carried, magnetic dust. The magnet arrays are provided by Denmark.
- Calibration Targets are reference points that will help scientists fine-tune
observations not only from imagers but also other science instruments. The
Mössbauer spectrometer, for example, uses as a calibration target a thin slab of
rock rich in magnetite. The alpha particle X-ray spectrometer uses a calibration
target on the interior surfaces of doors designed to protect its sensor head from
martian dust. The miniature thermal emission spectrometer has both an internal
target located in the mast assembly as well as an external target on the rover's
The panoramic camera's calibration target is, by far, the most unique the rover
carries. It is in the shape of a Sundial and is mounted on the rover deck. The
camera will take pictures of the sundial many times during the mission so that
scientists can make adjustments to the images they receive from Mars. They
will use the colored blocks in the corners of the sundial to calibrate the color in
images of the Martian landscape. Pictures of the shadows that are cast by the
sundial's center post will allow scientists to properly adjust the brightness of
each camera image. Children provided artwork for the sides of the base of the
Each rover also has other tools that, while primarily designed for engineering use in
the operation of the rover, can also provide information about the geology of the land-ing
- Hazard-Identification Cameras ride low on the front and rear of the rover.
The cameras are in stereo pairs at each location in order to produce three-dimensional
information about the terrain before or behind the rover. Each
hazard-identification camera provides a fisheye wide-angle view about 120
degrees across. They are sensitive to visible light and yield black-and-white
pictures. Onboard navigation software can analyze the images from these
cameras to identify obstacles and avoid them. The front pair of hazard
identification cameras provides position information to help movement of the
rover's arm and placement of arm-mounted tools on target rocks.
- The Navigation Camera is another stereo pair of black-and-white cameras.
Like the panoramic camera, it sits on top of the mast and can rotate and tilt.
Unlike the panoramic camera, it shoots wider-angle images (about 45 degrees
across, compared with about 16 degrees across for the panoramic camera) and
it does not have changeable filters to produce color images. Because of its
wider field of view, the navigation camera's images can give a quick full-circle
view of the surroundings at each new location that the rover reaches, requiring
less data-transmission time than would a full-circle set of panoramic camera
images. Engineers and scientists will use those images in planning where to
send the rover and where to use the science instruments for more detailed
- Each spacecraft has one more camera on the underside of the lander as a
key component in what is called the Descent Image Motion Estimation
Subsystem. The main purpose of this camera is to aid in safe landing by
providing information about how fast the spacecraft is moving horizontally in the
final half-minute of its descent. It will take a total of three black-and-white
images it takes from altitudes of up to about 2.4 kilometers (1.5 miles) above
ground, which may also provide scientists with a broader geological context
about the landing site.
- Wheels of the rover, in addition to providing mobility, may be used to dig
shallow trenches to evaluate soil properties and expose fresh soil to be