Mars Rover: The Owner’s Manual

Mars Rover: The Owner’s Manual

  • See gallery of Spirit’s Sol 1 images and slideshow
  • Phobos, meaning fear, and Deimos, meaning terror, are the two irregular moons on Mars, named after the god of war. The red planet has alternatively been described as the most promising location for evidence of ancient, non-terrestrial biology to the ‘Death Planet’. The planetary corpse image for Mars has come into circulation only recently because of the many missions that its difficult conditions have marooned. As one scientist quips, "Mars is a warm corpse if not a fire-breathing dragon."

    Delta rocket launch in summer 2003.
    Credit: NASA/JPL/Cornell University

    With its new, healthy ‘asset’ on Mars, what are NASA’s current plans for driving around the fourth rock from the sun?

    The present decade represents the most intense scientific exploration of a neighboring world since the Apollo era, focusing on the search for ancient and modern habitats through the history of water. The next decade will witness the transition of themes, from "following the water" to a "search for building blocks of life" — in other words, following the carbon.

    The exploration strategy on Mars is to uncover new insights into the red planet’s past, the history of its rocks and interior, the many roles and abundances of water and, quite possibly, evidence of past and present life.

    The facts of what face the science team for maneuvering their roving geologist are summarized in terse commands, just as the driving controls from Earth will move this mobile laboratory around rocks, off its landing petal, and eventually into the distant horizon seen in current panoramas. The rover is expected to witness up to ninety sunset drives, before mission planners reach their extended exploration scenarios.

    As noted by Dr. Ed Weiler, NASA Associate Administrator for Science, one first for this mission that paid off early, was the world’s only interplanetary satellite communication network. First images arrived via orbiters around Mars, as unique relay points for storing and transmitting the data-rich pictures only hours after touching down. Just some of the most significant findings from those two orbiters which have operated for years around Mars, but currently aid the landing missions, include:

    • evidence of possibly recent liquid water at the martian surface;
    • evidence for layering of rocks that points to widespread ponds or lakes in the planet’s early history;
    • topographic evidence that most of the southern hemisphere is higher in elevation than most of the northern hemisphere, so that any downhill flow of water and sediments would have tended to be northward;
    • identification of gray hematite, a mineral suggesting a wet environment when it was formed;
    • extensive evidence for the role of dust in reshaping the recent martian environment;
    • strong evidence for large quantities of frozen water mixed into the top layer of soil in the 20 percent of the planet near its north and south poles. By one estimate — likely an underestimate — the amount of water ice near the surface, if melted, would be enough water to fill Lake Michigan twice.

    The landing profile and spacecraft specifications offer a number of new milestones in robotic exploration on the surface.

    Airbag descent towards the surface of Mars
    Credit: NASA/JPL/Cornell University


    • Cruise vehicle dimensions: 2.65 meters (8.7 feet) diameter, 1.6 meters (5.2 feet) tall
    • Rover dimensions: 1.5 meter (4.9 feet) high by 2.3 meters (7.5 feet) wide by 1.6 meter (5.2 feet) long

    Weight: 1,062 kilograms (2,341 pounds) total at launch, consisting of

    • 174-kilogram (384 pound) rover,
    • 365-kilogram (805-pound) lander,
    • 198-kilogram (436-pound) backshell and parachute,
    • 90-kilogram (198-pound) heat shield and
    • 183-kilogram (403-pound) cruise stage,
    • plus 52 kilograms (115 pounds) of propellant

    Power: Solar panel and lithium-ion battery system providing 140 watts on Mars surface

    Science instruments:

    • Panoramic cameras,
    • miniature thermal emission spectrometer,
    • Mössbauer spectrometer,
    • alpha particle X-ray spectrometer,
    • microscopic imager,
    • rock abrasion tool,
    • magnet arrays, collect airborne dust for analysis by the science instruments. Mars is a dusty place, and some of that dust is highly magnetic.

    The science package, developed by international collaborators working with JPL and Cornell, is called Athena, consisting mainly of two instruments designed to survey the landing site, as well as three other instruments on an arm designed for closeup study of rocks. 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 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 new Pancam design has a camera bar that contains Pancam and Navcam (navigation camera) heads. A "visor" changes the elevation of the cameras so the rover can look up or down.
    Credit: Cornell University

    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 adjust the brightness of each camera image.

    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 examinations.

    The Mini-Thermal Emission Spectrometer (Mini-TES) 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.

    Dangling precariously between a supersonic parachute and the detached heatshield
    Credit: NASA/JPL/Cornell University

    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 formed.

    Because many of the most important minerals on Mars contain iron, the Mösbauer 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.

    First sunset on Mars, where each day, or sol, is slightly longer than an Earth-day
    Credit: NASA/JPL/Cornell University

    Spirit might not find any water-related rocks at all as it explores the landing-site region. Even if a lake once covered the Gusev floor, later deposits, such as ash from a volcanic area north of Gusev, could have thoroughly buried sedimentary evidence of the lake. Using the three instruments that look to analyze the composition of rocks and soils, scientists may use them to look for evidence such as:

    • Weathering. Interaction with water can alter the chemical composition of rock-forming material. The water’s temperature affects those changes. Information from the spectrometers could thus provide evidence about the wetness and temperature of the past environment, two key factors in whether that environment was hospitable to life.
    • Evaporites. Some minerals are formed when dissolved salts get left behind as water evaporates. Finding and identifying any "evaporite" minerals at Gusev would suggest that the crater once held a salty, shallow lake.
    • Carbonates. Carbonate minerals, such as limestone, can form from chemical reactions that pull carbon dioxide out of the atmosphere into bodies of water. If Spirit’s spectrometers identify carbonate rocks, images from the rover’s cameras could yield clues about how long the environment stayed wet and whether water was in the form of hot springs.

    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 examined.

    The rock abrasion tool could provide the cameras with fresh, unweathered surfaces to examine. The types of traits scientists may be checking for include:

    • Grain size. Larger particles can settle out of water even when the water is moving. Smaller ones form sediments where water is still. The size of the particles that are consolidated into a sedimentary is a major clue about the conditions that existed when the sediments accumulated.
    • Grain uniformity. A sedimentary rock with an assortment of grain sizes suggests jumbling by dynamic conditions such as a mudslide or a variable current. Uniformity of grain size suggests more stable conditions over time.
    • Grain angularity. The shapes of grains in a sedimentary rock may be sharply angular or may be more rounded. Round grains tell a geologist that they may have worn off their edges by tumbling in a river for a long distance from where they started.
    • Cross-bedding. Some sedimentary rocks have evenly stacked, horizontal layering; others have some layers at an angle to the stack. This second pattern, called cross-bedding, can result from an episode of migrating sand waves or ripples creating cyclical patterns of sediments that build up, then partially erode away, then rebuild.
    • Fine layering. On Earth, some sedimentary rocks show annual layers that result from seasonal changes in the environment, like the growth rings of trees. Layers resulting from faster deposition in one season alternate with layers resulting from slower deposition the rest of the year. Scientists will be watching for anything similar in Mars rocks.

    Spirit and Opportunity science goals

    Objectives for the missions include:

    • 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 twin lander profile for Spirit and Opportunity was first successfully deployed in the 1970’s by the two Viking missions, I and II. Just as one character, industrialist S.R. Hadden, says in Carl Sagan’s movie, Contact: "First rule in government spending: why build one when you can have two, twice the price". Associate Administrator for Science, Weiler, offered this scenario in 1999, when the Mars program was retooled by giving the Jet Propulsion Lab, ‘literally fifteen minutes’ to accept the challenge to fly two identical missions in their current exploration series. The Spirit and Opportunity rovers are as ‘identical as can be’ according to Project Manager, Pete Theisinger, since the twins were built at the same time, launched less than a month apart, and land over a three week span. The difference is only in their broadcast frequency. The second rover, Opportunity, will target a site nearly a hemisphere away from Spirit, near the equator, but on opposite sides of the planet.

    Spirit Mission

    • Launch vehicle: Delta II 7925
    • Launch: June 10, 2003, from Cape Canaveral Air Force Station, Fla.
    • Earth-Mars distance at launch: 103 million kilometers (64 million miles)
    • Mars landing: Jan. 4, 2004, at about 2:30 p.m. local Mars time (signal received at Earth 8:35 p.m. PST Jan. 3)
    • Landing site: Gusev Crater, possible former lake in giant impact crater
    • Earth-Mars distance on landing day: 170.2 million kilometers (105.7 million miles)
    • One-way speed-of-light time Mars-to-Earth on landing day: 9.46 minutes
    • Total distance traveled Earth to Mars (approximate): 487 million kilometers (303 million miles)
    • Near-surface atmospheric temperature at landing site: -100 C (-148 F) to 0 C (32 F)
    • Primary mission: 90 Mars days, or "sols" (equivalent to 92 Earth days)

    Opportunity Mission

    • Launch vehicle: Delta II 7925H (larger solid-fuel boosters than 7925)
    • Launch: July 7, 2003, from Cape Canaveral Air Force Station, Fla.
    • Earth-Mars distance at launch: 78 million kilometers (48 million miles)
    • Mars landing: Jan. 25, 2004, at about 1:15 p.m. local
    • Mars time (signal received at Earth 9:05 p.m. PST Jan. 24)
    • Landing site: Meridiani Planum, where mineral deposits suggest wet past
    • Earth-Mars distance on landing day: 198.7 million kilometers (123.5 million miles)
    • One-way speed-of-light time Mars-to-Earth on landing day: 11 minutes
    • Total distance traveled Earth to Mars (approximate): 456 million kilometers (283 million miles)
    • Near-surface atmospheric temperature at landing site: -100 C (-148 F) to 0 C (32 F)
    • Primary mission: 90 Mars days, or "sols" (equivalent to 92 Earth days)

    Program Cost:

    • Approximately $820 million total, consisting of
    • $645 million spacecraft development and science instruments;
    • $100 million launch;
    • $75 million mission operations and science processing

    Landing sites

    More than 100 scientists and engineers participated in evaluating sites both on the basis of favorable criteria for safe landings and on the prospects for outstanding science opportunities after the rovers reach the ground. To qualify for consideration, candidate sites had to be near Mars’ equator, not too rugged, not too rocky, not too dusty, and low enough in elevation so the spacecraft would pass through enough atmosphere to slow down sufficiently. In all, 155 potential sites met the initial safety constraints.


    The first Mars Exploration Rover, Spirit, is flying to Gusev Crater, a bowl bigger than Connecticut that appears to have held a lake long ago. Gusev Crater was named in 1976 for Russian astronomer Matvei Gusev, who lived from 1826 to 1866. Scientists will use the robot’s instruments to seek and analyze geological evidence about past environmental conditions in the crater. If sedimentary rocks lie on the surface, they may yield telltale clues to whether the crater ever did hold a wet environment that might have been suitable for sustaining life. An asteroid or comet impact perhaps as much as 4 billion years ago dug Gusev Crater. Many smaller, younger impact craters pock Gusev’s 150-kilometer-diameter (95-mile) floor.

    Montage of first-light images from Spirit. Shown are top view, horizon, airbag and egress path. Inset is the color calibration target that doubles as an interplanetary sundial.

    One of the largest branching valleys on Mars, likely carved by flowing water more than 2 billion years ago, leads directly into Gusev Crater through a breach in the crater’s southern rim. Gusev sits at 15 degrees latitude south of Mars’ equator at longitude 184.7 degrees west, in a transition zone between the ancient highlands on the southern part of the planet and smoother plains to the north. The valley, called Ma’adim Vallis, snakes northward Nile-like about 900 kilometers (550 miles) from the highlands to Gusev. In places, it gapes more than 25 kilometers (16 miles) wide and 2 kilometers (1.2 miles) deep. Ma’adim Vallis takes its name from the Hebrew word for Mars. Water flowing down the valley would have pooled in Gusev Crater, dropping sediments there before exiting through a gap in the crater’s northern rim. Comparable crater lakes, such as Lake Bosumtwi in Ghana, exist on Earth. Gusev’s lake, if indeed it did exist, is now gone. But the floor of Gusev Crater may hold water-laid sediments that preserve records of the lake environment, of the sediments’ highlands origins and of the sediments’ river trip.

    As a potential complication, sedimentary layers may lie buried under later deposits from volcanic eruptions or wind-blown dust. If so, the best chances for finding sedimentary rocks may be in material thrown outward when younger craters were excavated by impacts that punched through the covering layers. The targeted landing area for Spirit is an ellipse about 78 kilometers (48 miles) long and 10.4 kilometers (6.5 miles) wide near the center of Gusev Crater. Several small craters in and near the ellipse have likely stirred up rocks from underneath the top veneer of Gusev’s flat floor. Whether they have dug deep enough to expose lake-related material if volcanic overburden is deep remains to be seen.


    The second Mars Exploration Rover, Opportunity, is targeted for Meridiani Planum, a smooth plain near the equator halfway around the planet from Gusev Crater. "Planum" means plains, and the name fits: Meridiani Planum is one of the smoothest, flattest places on Mars. Gusev Crater and Meridian Planum do have something in common.

    Intense scientific interest in the site results not from the shape of the terrain, as at Gusev, but from an unusual mineral deposit found by a Mars-orbiting spacecraft. Scientists using an instrument called the thermal emission spectrometer on NASA’s Mars Global Surveyor have discovered that Meridiani Planum is rich in gray hematite, a type of iron oxide mineral. On Earth, gray hematite usually — but not always — forms in association with liquid water. Some environmental conditions that can produce gray hematite, such as a lake or hot springs, could be quite hospitable to life. Others, such as hot lava, would not. The gray hematite covers an estimated 15 to 20 percent of the surface in the vicinity of the planned landing site. It appears as a dark cap layer atop a brighter layer that is exposed at many places within the ellipse-shaped landing target.

    Each rover does a ‘stand-up’ maneuver, wheel release, and egress or exit from its landing petal. From this point onwards the rover is able to travel up to 100 meters per day. JPL Center Director described this roving ability as the equivalent of multiple landing sites every day.
    Credit: NASA/JPL/Cornell University

    With the tools on Opportunity, scientists hope to determine which type of hematiteforming environment existed at Meridiani. Each of several possible past environments might leave geological clues to distinguish it from the others. For example:

    • Gray hematite can form in oxygenated water in an iron-rich lake or ocean. If Opportunity finds evidence of sedimentary layering in rocks associated with a Meridiani hematite outcropping, that would support such a scenario possibly hospitable to life.
    • As it percolates through the ground, iron-rich water heated by underground volcanism can deposit veins of gray hematite. This type of "hydrothermal" environment could offer microbes a favorable habitat. It would likely leave behind other types of telltale minerals that Opportunity’s instruments could identify, such as carbonates.
    • Weathering in the presence of very small amounts of liquid water can create a veneer of gray hematite on rocks bearing other types of iron oxide. Scientists using the rock abrasion tool and two spectrometers on the rover’s arm may determine whether the hematite at Meridiani fits this pattern.
    • Gray hematite can result from direct oxidation of hot, iron-rich lava. This process requires no liquid water and would not indicate a past environment hospitable to life. If Opportunity finds only volcanic rocks at Meridiani, that would support this scenario.

    The geographical coordinates for the center of Opportunity’s landing target are 1.98 degrees south latitude and 5.94 degrees west longitude. The targeted landing area is an ellipse about 85 kilometers (53 miles) long and 11 kilometers (6.8 miles) wide. The site is within a large region that has been known as Meridiani since the earliest days of telescopic study of Mars because it lies near the planet’s arbitrarily designated prime meridian, or line of zero longitude.

    Planet at a Glance


    • One of five planets known to ancients;
    • Mars was Roman god of war, agriculture and the state
    • Yellowish brown to reddish color;
    • occasionally the third brightest object in the night sky after the Moon and Venus

    Physical Characteristics

    • Average diameter 6,780 kilometers (4,212 miles);
    • about half the size of Earth, but twice the size of Earth’s Moon
    • Same land area as Earth, reminiscent of a rocky desert
    • Mass 1/10th of Earth’s;
    • gravity only 38 percent as strong as Earth’s
    • Density 3.9 times greater than water (compared to Earth’s 5.5 times greater than water)
    • No planet-wide magnetic field detected; only localized ancient remnant fields in various regions


    • Fourth planet from the Sun, the next beyond Earth
    • About 1.5 times farther from the Sun than Earth is
    • Orbit elliptical;
    • distance from Sun varies from a minimum of 206.7 million kilometers (128.4 millions miles) to a maximum of 249.2 million kilometers (154.8 million miles);
    • average distance from the Sun 227.7 million kilometers (141.5 million miles)
    • Revolves around Sun once every 687 Earth days
    • Rotation period (length of day) 24 hours, 39 min, 35 sec (1.027 Earth days)
    • Poles tilted 25 degrees, creating seasons similar to Earth’s Environment

    Atmosphere composed chiefly of

    • carbon dioxide (95.3%),
    • nitrogen (2.7%) and
    • argon (1.6%)
    • Surface atmospheric pressure less than 1/100th that of Earth’s average
    • Surface winds up to 80 miles per hour (40 meters per second)
    • Local, regional and global dust storms; also whirlwinds called dust devils

    Surface temperature

    • averages -53 C (-64 F);
    • varies from -128 C (-199 F) during polar night to 27 C (80 F) at equator during midday at closest point in orbit to Sun


    • Highest point is Olympus Mons, a huge shield volcano about 26 kilometers (16 miles) high and 600 kilometers (370 miles) across; has about the same area as Arizona
    • Canyon system of Valles Marineris is largest and deepest known in solar system; extends more than 4,000 kilometers (2,500 miles) and has 5 to 10 kilometers (3 to 6 miles) relief from floors to tops of surrounding plateaus
    • "Canals" observed by Giovanni Schiaparelli and Percival Lowell about 100 years ago were a visual illusion in which dark areas appeared connected by lines.
    • The Mariner 9 and Viking missions of the 1970s, however, established that Mars has channels possibly cut by ancient rivers Moons
    • Two irregularly shaped moons, each only a few kilometers wide
    • Larger moon named Phobos ("fear"); smaller is Deimos ("terror"), named for attributes personified in Greek mythology as sons of the god of war

    Martian Exploration Vitae

    Mars, named after the Roman god of war, has recently acquired jargon seemingly borrowed from science fiction, as the Death Planet. Its record for frustrating mission planners dates back to the beginning of space exporation. During the Apollo moon program, six manned vehicles reached the surface over three years; in four decades, only four robotic vehicles have safely reached the surface of Mars, with an overall 66% failure rate. The chronology of historical Mars missions are shown by mission, country, launch date, purpose and results, including what the next generation may offer for exploration on the red planet.

    • [Unnamed], USSR, 10/10/60, Mars flyby, did not reach Earth orbit
    • [Unnamed], USSR, 10/14/60, Mars flyby, did not reach Earth orbit
    • [Unnamed], USSR, 10/24/62, Mars flyby, achieved Earth orbit only
    • Mars 1, USSR, 11/1/62, Mars flyby, radio failed at 106 million km (65.9 million miles)
    • [Unnamed], USSR, 11/4/62, Mars flyby, achieved Earth orbit only
    • Mariner 3, U.S., 11/5/64, Mars flyby, shroud failed to jettison
    • Mariner 4, U.S. 11/28/64, first successful Mars flyby 7/14/65, returned 21 photos
    • Zond 2, USSR, 11/30/64, Mars flyby, passed Mars but radio failed, returned no planetary data
    • Mariner 6, U.S., 2/24/69, Mars flyby 7/31/69, returned 75 photos
    • Mariner 7, U.S., 3/27/69, Mars flyby 8/5/69, returned 126 photos
    • Mariner 8, U.S., 5/8/71, Mars orbiter, failed during launch
    • Kosmos 419, USSR, 5/10/71, Mars lander, achieved Earth orbit only
    • Mars 2, USSR, 5/19/71, Mars orbiter/lander arrived 11/27/71, no useful data, lander burned up due to steep entry
    • Mars 3, USSR, 5/28/71, Mars orbiter/lander, arrived 12/3/71, lander operated on surface for 20 seconds before failing
    • Mariner 9, U.S., 5/30/71, Mars orbiter, in orbit 11/13/71 to 10/27/72, returned 7,329 photos
    • Mars 4, USSR, 7/21/73, failed Mars orbiter, flew past Mars 2/10/74
    • Mars 5, USSR, 7/25/73, Mars orbiter, arrived 2/12/74, lasted a few days
    • Mars 6, USSR, 8/5/73, Mars flyby module and lander, arrived 3/12/74, lander failed due to fast impact
    • Mars 7, USSR, 8/9/73, Mars flyby module and lander, arrived 3/9/74, lander missed the planet
    • Viking 1, U.S., 8/20/75, Mars orbiter/lander, orbit 6/19/76-1980, lander 7/20/76-1982
    • Viking 2, U.S., 9/9/75, Mars orbiter/lander, orbit 8/7/76-1987, lander 9/3/76-1980; combined, the Viking orbiters and landers returned 50,000+ photos
    • Phobos 1, USSR, 7/7/88, Mars/Phobos orbiter/lander, lost 8/88 en route to Mars
    • Phobos 2, USSR, 7/12/88, Mars/Phobos orbiter/lander, lost 3/89 near Phobos
    • Mars Observer, U.S., 9/25/92, lost just before Mars arrival 8/21/93
    • Mars Global Surveyor, U.S., 11/7/96, Mars orbiter, arrived 9/12/97, high-detail mapping to the resolution of a school-bus through 1/00, now conducting second extended mission through fall 2004 Mars 96, Russia, 11/16/96, orbiter and landers, launch vehicle failed
    • Mars Pathfinder, U.S., 12/4/96, Mars lander and rover, landed 7/4/97, last transmission 9/27/97
    • Nozomi, Japan, 7/4/98, Mars orbiter, currently in orbit around the Sun; Mars arrival delayed to 12/13/03 due to propulsion problem; diverted to bypass Mars
    • Mars Climate Orbiter, U.S., 12/11/98, lost upon arrival 9/23/99
    • Mars Polar Lander/Deep Space 2, U.S., 1/3/99, lander and soil probes, lost on arrival 12/3/99
    • Mars Odyssey, U.S., 3/7/01, Mars orbiter, arrived 10/24/01, currently conducting prime mission studying global composition, ground ice, thermal imaging
    • Mars Express/Beagle 2, European Space Agency, 6/2/03, Mars orbiter/lander, entered orbit 12/25/03, landing 12/25/03 (no signal from lander 01/03)
    • Mars Exploration Rover, US, 1/3/03, Mars rover, Spirit, landed 1/3/03, 90 days on surface
    • Mars Exploration Rover, US, 1/26/03, Mars rover, Opportunity, to land 1/26/03, 90 days on surface, identical twin to Spirit
    • Mars Reconnaissance Orbiter (2005), US, ground-penetrating radar and telescopic camera will reveal martian landscapes in resolution fine enough to show rocks the size of a desk
    • Phoenix Mars Scout (2007), US, land in May 2008, to land near arctic ground in an ice-rich region of northern Mars, scoop up soil to analyze at the landing site, and radio home evidence about the history of martian water and the possibility of past or current life
    • Mars Science Laboratory (2009), US, baselined as nuclear-powered, capable of moving on the surface for a full martian year or longer, traveling ten times further than Mars Exploration rovers (> 1000 meters)

    Earth analogs

    What is Mars most like, in comparison to places on Earth?

    New four-pack. From left, four previous landing sites, Viking 1-2, Pathfinder and Spirit (right)
    Credit: NASA/ JPL

    Astrobiology Chris McKay has compared Gusev Crater to a dry, cold spot–Lake Vanda, Antarctica. Gusev is also a crater that may have eventually pooled enough water to qualify as a temporary lake. Lake Bosumtwi in Ghana is the most well-known crater lake on Earth.

    Based on what they have learned from spacecraft missions, scientists view Mars as the "in-between" planet of the inner solar system. Small rocky planets such as Mercury and Earth’s Moon apparently did not have enough internal heat to power volcanoes or to drive the motion of tectonic plates, so their crusts grew cold and static relatively soon after they formed when the solar system condensed into planets about 4.6 billion years ago.

    Devoid of atmospheres, they are riddled with craters that are relics of impacts during a period of bombardment when the inner planets were sweeping up remnants of small rocky bodies that failed to "make it as planets" in the solar system’s early times. Earth and Venus, by contrast, are larger planets with substantial internal heat sources and significant atmospheres. Earth’s surface is continually reshaped by tectonic plates sliding under and against each other and materials spouting forth from active volcanoes where plates are ripped apart. Both Earth and Venus have been paved over so recently that both lack any discernible record of cratering from the era of bombardment in the early solar system.

    Mars appears to stand between those sets of worlds, on the basis of current yet evolving knowledge. Like Earth and Venus, it possesses a myriad of volcanoes, although they probably did not remain active as long as counterparts on Earth and Venus. On Earth, a single "hot spot" or plume might form a chain of middling-sized islands such as the Hawaiian Islands as a tectonic plate slowly slides over it. On Mars there are apparently no such tectonic plates, at least as far as we know today, so when volcanoes formed in place they had the time to become much more enormous than the rapidly moving volcanoes on Earth. Overall Mars appears to be neither as dead as Mercury and our Moon, nor as active as Earth and Venus.

    Thanks to the ongoing observations by the Global Surveyor and Odyssey orbiters, however, this view of Mars is still evolving. Mars almost resembles two different worlds that have been glued together. From latitudes around the equator to the south are ancient highlands pockmarked with craters from the solar system’s early era, yet riddled with channels that attest to the flow of water. The northern third of the planet, however, overall is sunken and much smoother at kilometer (mile) scales. There is as yet no general agreement on how the northern plains got to be that way.

    At one end of the spectrum is the theory that it is the floor of an ancient sea; at the other, the notion that it is merely the end product of innumerable lava flows.

    Driving up to a rock, scraping it clean if dusty, and extending an arm-like geology tools are the major roving activities for science opportunities.
    Credit: NASA/JPL/Cornell University

    New theories are emerging thanks to the discoveries of Mars Odyssey, and some scientists believe a giant ice sheet may be buried under much of the relatively smooth northern plains. Many scientists suspect that some unusual internal process not yet fully understood may have caused the northern plains to sink to relatively low elevations in relation to the southern uplands.

    The Three Martian Ages

    Scientists today view Mars as having had three broad ages, each named for a geographic area that typifies it.

    The Noachian Era is the name given to the time spanning perhaps the first billion years of Mars’ existence after the planet was formed 4.6 billion years ago. In this era, scientists suspect that Mars was quite active with periods of warm and wet environment, erupting volcanoes and some degree of tectonic activity. The planet may have had a thicker atmosphere to support running water, and it may have rained and snowed.

    In the Hesperian Era, which lasted for about the next 500 million to 1.5 billion years, geologic activity was slowing down and near-surface water perhaps was freezing to form surface and buried ice masses. Plunging temperatures probably caused water pooled underground to erupt when heated by impacts in catastrophic floods that surged across vast stretches of the surface — floods so powerful that they unleashed the force of thousands of Mississippi Rivers. Eventually, water became locked up as permafrost or subsurface ice, or was partially lost into outer

    The Amazonian Era is the current age that began around 2 billion to 3 billion years ago. The planet is now a dry, desiccating environment with only a modest atmosphere in relation to Earth. In fact, the atmosphere is so thin that water can exist only as a solid or a gas, not as a liquid. Apart from that broad outline, there is lively debate and disagreement on the details of Mars’ history.

    How wet was the planet, and how long ago? What eventually happened to all of the water?

    That is all a story that is still being written.

    Related Web Pages

    Postcards from Mars
    Spirit’s First Light
    Ancient Lakebed: Spirit Has Landed