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The Mars Pathfinder (MESUR Pathfinder) later called The Carl Sagan Memorial Station was launched on December 4, 1996 by NASAmarker aboard a Delta II just a month after the Mars Global Surveyor was launched. After a 7-month voyage it landed on Ares Vallismarker, in a region called Chryse Planitia on Mars, in the Oxia Palus quadrangle, on 4 July 1997. During its voyage the spacecraft had to accomplish four flight adjustments on 10 January, 3 February, 6 May and 25 June. The lander opened, exposing the rover called Sojourner that would go on to execute many experiments on the Martian surface.

The mission carried a series of scientific instruments to analyze the Martian atmosphere, climate, geology and the composition of its rocks and soil. It was the second project from NASA's Discovery Program, which promotes the use of low-cost spacecraft and frequent launches under the motto "cheaper, faster and better" promoted by the then administrator, Daniel Goldin. The mission was directed by the Jet Propulsion Laboratorymarker (JPL), a division of the California Institute of Technologymarker, responsible for NASA's Mars Exploration Program.

This mission to Mars, besides being the first of a series of missions to Mars that included rovers (robotic exploration vehicles), was the most important since the Vikings landed on the red planet in 1976, and also was the first successful mission to send a rover to a planet. The then still extant Soviet Unionmarker successfully sent rovers to the Moon as part of the Lunokhod programme in the 1970s, but its two attempts to send rovers in the Mars probe program failed.

In addition to scientific objectives, the Mars Pathfinder mission was also a "proof-of-concept" for various technologies, such as airbag-mediated touchdown and automated obstacle avoidance, both later exploited by the Mars Exploration Rovers. The Mars Pathfinder was also remarkable for its extremely low price relative to other unmanned space missions to mars. Originally, the mission was conceived as the first of the Mars Environmental Survey (MESUR) program.

Mission overview

Mars Pathfinder launched on 4 December 1996

The lander relayed transmissions to and from the robot, allowing it to operate independently of the probe body. The robot was remotely controlled, but had a basic camera-assisted autonomous control system allowing it to navigate and negotiate minor obstacles without operator intervention.

The robot's freedom of movement allowed the exploration team to closely analyze many more rocks and soil samples than with a traditional probe. From its landing in July 4, 1997 until the final data transmission on September 27, 1997, Mars Pathfinder returned 16,500 images from the lander and 550 images from the rover, as well as more than 15 chemical analyses of rocks and soil and extensive data on winds and other weather factors. Findings from the investigations carried out by scientific instruments on both the lander and the rover suggest that Mars was at one time in its past warm and wet, with water existing in its liquid state and a thicker atmosphere.

The lander and rover performed for much longer and better than expected, but eventually contact with the lander was lost on sol 83. The lander's silver-zinc battery was only capable of being recharged about 40 times, as a consequence after about 40 sols, the battery was not able to keep the lander warm at night. The exact reason for the final failure of the lander is not certain, but it was probably due to an electronics failure due to the very cold night-time temperatures that were experienced in the final weeks of the mission. After sol 92, the automatic backup procedures should have instructed the rover to return to the lander and circle it while attempting to re-establish communications. This behavior would have continued until hardware failure. The lack of communication may mean that the rover's final location and state are unknown. NASA's efforts to recontact Pathfinder ended on March 10, 1998.

Mission objectives

  • To prove that the development of "faster, better and cheaper" spacecraft is possible (with three years for development and a cost under $150 million).
  • To show that it is possible to send a load of scientific instruments to another planet with a simple system and at one fifteenth the cost of a Viking mission. (For comparison, the Viking missions cost $935 million in 1974 or $3.5 billion in 1997 dollars)
  • To demonstrate NASA's commitment to low-cost planetary exploration by finishing the mission with a total expenditure of $280 million, including the launch vehicle and mission operations.
The project manager was Tony Spear.

The probe

The probe consisted of a lander and a lightweight (10.6 kilograms/23 pounds) wheeled robot (Rover) called Sojourner ("one in a break from journeying"), after the slave and abolitionist Sojourner Truth. [26671] (See below for the selection of the name.)

Mission equipment

1990s concept illustration of lander and rover
Mars Pathfinder lander IMP
Actual 1997 image from the IMP after landing on Mars

The Mars Pathfinder executed different investigations on the Martian soil using three scientific instruments. The lander contained a stereoscopic camera with spatial filters on an expandable pole called Imager for Mars Pathfinder (IMP), and the Atmospheric Structure Instrument/Meteorology Package (ASI /MET) which acts as a Mars meteorological station, collecting data about pressure, temperature, and winds. The MET structure included three windsocks mounted at three heights on a pole, the topmost at about one meter (yard) and generally registered winds from the West.

The Sojourner rover had a Alpha Proton X-ray Spectrometer (APXS), which was used to analyze the components of the rocks and soil. The rover also had two black and white cameras and a color one. These instruments could make investigations of the geology of the Martian surface from just a few millimeters to many hundreds of meters, the geochemistry and evolutionary history of the rocks and surface, the magnetic and mechanical properties of the land, as well as the magnetic properties of the dust, atmosphere and the rotational and orbital dynamics of the planet.

Mars Pathfinder Lander:
  1. Imager for Mars Pathfinder (IMP), (includes magnetometer and anemometer)
  2. Atmospheric and meteorological sensors (ASI/MET)

Mars Pathfinder Sojourner Rover:
  1. Imaging system (three cameras: front B&W stereo, 1 rear color)
  2. Laser striper hazard detection system
  3. Alpha Proton X-ray Spectrometer (APXS)
  4. Wheel Abrasion Experiment
  5. Material Adherence Experiment
  6. Accelerometers
  7. Potentiometers

Scientific objectives

  • Surface morphology and geology using scaled measurements.
  • Petrology and geochemistry of surface materials.
  • Magnetic and mechanical properties of the surface.
  • Atmospheric structure, besides diurnal and nocturnal meteorological variations.
  • Rotational and orbital dynamics of Mars.

Pathfinder found temperatures varied on a diurnal cycle with the coldest just before sunrise about -78 Celsius with the warmest just after Mars noon about -8 Celsius. These extremes occurred near the ground which both warmed up and cooled down fastest. Temperatures further from the ground at 1.4 m (4.3 feet) were about 10 degrees inside these ranges (-70 at night, to -18 at day). Pathfinder measured temperatures at three heights above the surface: 0.65, 0.9 and 1.4 meters. Weather observations suggest that cold morning air was warmed by the ground and rose in small eddies.

Surface pressures varied diurnally over a 0.2 millibar range, but showed 2 daily minimums and two daily maximums. The average daily pressure decreased from about 6.75 millibars to a low of just under 6.7 millbars, corresponding to when the maximum amount of carbon dioxide has condensed on the south pole. Winds were usually less than 10m/s. Dust devils were detected in the early afternoon.

The sky had a pink color. There was evidence of clouds and possibly fog.

The Mars Pathfinder found its landing site to contain a great deal of rocks. Analysis shows the area to have a greater density of rocks than 90% of the Mars. Some of the rocks leaned against each other in a manner geologists term imbricated. It is believed strong flood waters in the past pushed the rocks around to face away from the flow. Some pebbles were rounded, perhaps from being tumbled in a stream. Some rocks have holes on their surfaces that seem to have been fluted by wind action. Some small sand dunes are present. Parts of the ground are crusty, maybe due to cementing by a fluid containing minerals. In gereral the rocks show a dark gray color with patches of red dust and/or weathered appearance on their surfaces. Dust covers the lower 5–7 cm of some rocks, so they may have once been buried, but have now become exhumed. Three knobs, one large crater, and two small craters were visible on the horizon.

Other results from Pathfinder

By taking multiple images of the sky at different distances from the sun, scientists were able to determine that size of the particles in the pink haze was about 1 micrometer in radius. The color of some soils was similar to that of an iron oxyhydroxide phase which would support the theory of a warmer and wetter climate in the past.
 Pathfinder carried a series of magnets to examine the magnetic component of the dust. Eventually, all but one of the magnets developed a coating of dust. Since the weakest magnet did not attract any soil, it was concluded that the airborne dust did not contain pure magnetite or just one type of maghemite. The dust probably was an aggregate possible cemented with ferric oxide (Fe2O3). Using much more sophisticated instruments, Mars Spirit Rover found that magnetite could explain the magnetic nature of the dust and soil on Mars. Magnetite was found in the soil and that the most magnetic part of the soil was dark. Magnetite is very dark.

Using Doppler tracking and two-way ranging, scientists added earlier measurements from the Viking landers to determine that the non-hydrostatic component of the polar moment of inertia is due to the Tharsis bulge and that the interior is not melted. The central metallic core is between 1300 km and 2000 km in radius.

Landing site

The landing site was an ancient flood plain in Mars's northern hemisphere called "Ares Vallismarker" ("the valley of Ares," the Ancient Greek equivalent of the Ancient Roman deity Mars) and is among the rockiest parts of Mars. Scientists chose it because they found it to be a relatively safe surface to land on and one that contained a wide variety of rocks deposited during a catastrophic flood. After the landing, at coordinates 19.13 degrees north, 33.22 degrees west, succeeded, the landing site received the name The Carl Sagan Memorial Station in honor of the late astronomer and leader in the field of robotic spacecraft missions.

Landing process

Mars Pathfinder entered the Martian atmosphere and landed using an innovative system involving an entry capsule, a supersonic parachute, followed by solid rockets and large airbags to cushion the impact.

Pathfinder lands

Sojourner rover

The Sojourner rover' was the second space exploration rover to successfully reach another planet, and the first to actually be deployed on another planet. Sojourner landed on Mars as part of the Mars Pathfinder mission on July 4, 1997.

The on-board computer

The embedded computer on board the Sojourner rover was based around the 100 KHz Intel 80C85 CPU with 512 KB of RAM and 176 KB of flash memory solid-state storage.

The Sojourner gets out

Sojourner rover
Sojourner's exit from the lander occurred on Sol 2, after its landing in July 4, 1997. As the next sols progressed it approached some rocks which were named (by the scientists) "Barnacle Billmarker", "Yogimarker", and "Scooby Doo", after the famous cartoons. The rover made measurements of the elements found in those rocks and in the martian soil, while the lander took pictures of the Sojourner and the surrounding terrain, besides making climate observations.

The Sojourner is a six-wheeled 65 cm long vehicle, 48 cm wide, 30 cm tall and weighs 10.5 kg. When operating, it could move about 500 meters from the lander and its maximum speed reached one centimeter per second. During its 83 sol of operation, it sent 550 photographs to Earth and analyzed the chemical properties of sixteen locations near the lander.

Sojourner's rock analysis

The first analysis on a rock started on Sol 3 with "Barnacle Billmarker". The Alpha Proton X-ray Spectrometer (APXS) was used to determine its composition, the spectrometer taking ten hours to make a full scan of the sample. It found all the elements except hydrogen, which constitutes just 0.1% of the rock's or soil's mass.

The APXS works by irradiating rocks and soil samples with alpha particles (helium nuclei, which consist of two protons and two neutrons). The results indicated that "Barnacle Bill" is much like Earth's andesites, confirming past volcanic activity. The discovery of andesites shows that some Martian rocks have been remelted and reprocessed. On Earth, Andesite forms when magma sits in pockets of rock while some of the iron and magnesium settle out. Consequently, the final rock contains less iron and magnesiums and more silica. Volcanic rocks are usually classified by comparing the relative amount of alkalis (Na2O and K2O) with the amount of silica (SiO2). Andesite is different than the rocks found in meteorites that have come from Mars.

Analysis of "Yogimarker" rock again using the APXS showed that it was a basaltic rock, more primitive than "Barnacle Bill". Yogi's shape and texture show that it was probably deposited there by a flood.

Another rock, named "Moe", was found to have certain marks on its surface, demonstrating erosion caused by the wind. Most rocks analyzed showed a high content of silicon. In another region known as Rock Garden the Sojourner encountered crescent Moon-shaped dunes, which are similar to crescentic dunes on Earth.

By the time that final results of the mission were described in a series of articles in the Journal Science 9, December 5, 1997), it was believed that the rock Yogi contained a coating of dust, but was similar to the rock Barnacle Bill. Calculations suggest that the two rocks contain mostly the minerals orthopyroxene (magnesium-iron silicate), feldspars (aluminum silicates of potassium, sodium, and calcium), quartz (silicon dioxide), with smaller amounts of magnetite, ilmenite, iron sulfide, and calcium phosphate.

The lander, on the other hand, sent more than 16,500 pictures and made 8.5 million measurements of the atmospheric pressure, temperature and wind speed.

End of the mission

Close-up of Mars sky at sunset, showing more color variation, as imaged by Mars Pathfinder

Although the mission was programed to last a week to a month, it eventually lasted for almost three months. The final contact with the Pathfinder was at 10:23 UTC on September 27, 1997. Although the mission planners tried to restore contact during the following five months, the successful mission was terminated on March 10, 1998. After the landing, the Mars Pathfinder was renamed as the Sagan Memorial Station in honor of the famous astronomer and planetologist Carl Sagan. The mission had exceeded its goals in the first month.

The Mars Pathfinder entry descent and landing system design was used (with some modification) on the Mars Exploration Rover mission. Likewise many design aspects of Sojourner rover (e.g. the rocker-bogie mobility architecture and the navigation algorithms) were also successfully used on the Mars Exploration Rover mission.

Mars Reconnaissance Orbiter may have spotted Pathfinder in January 2007.

Naming the rover

The name Sojourner was chosen for the Mars Pathfinder rover after a year-long, worldwide competition in which students up to 18 years old were invited to select a heroine and submit an essay about her historical accomplishments. The students were asked to address in their essays how a planetary rover named for their heroine would translate these accomplishments to the Martian environment.

Initiated in March 1994 by The Planetary Society of Pasadena, CA, in cooperation with NASA's Jet Propulsion Laboratory (JPL), the contest got under way with an announcement in the January 1995 issue of the National Science Teachers Association's magazine "Science and Children," which is circulated to 20,000 teachers and schools across the nation.

Valerie Ambroise, 12, of Bridgeport, CT, submitted the winning essay about Sojourner Truth, an African-American reformist who lived during the Civil War era. An abolitionist and champion of women's rights, Sojourner Truth, whose legal name was Isabella Van Wagener, made it her mission to "travel up and down the land," advocating the rights of all people to be free and the rights of women to participate fully in society. The name Sojourner was selected because it means "traveler." JPL scientists and engineers working on the Mars Pathfinder project and Planetary Society staff members reviewed the 3,500 total entries received from all over the world, including essays from students living in Canada, India, Israel, Japan, Mexico, Poland and Russia. Nearly 1,700 of the essays were submitted by students aged 5 to 18 years old.

The selection of winners from this group by representatives from JPL and NASA Headquarters was based on several factors: the quality and creativity of the essay, taking into consideration the age of each contestant, the appropriateness of the name for a Mars rover, and the knowledge of the heroine, and the understanding of the Pathfinder rover's mission conveyed in the essay.

The second place prize winner was Deepti Rohatgi, 18, of Rockville, MD, who proposed naming the rover after Marie Curie, a Polish-born chemist who won the Nobel Prize in 1911 for her discovery of the elements radium and polonium. The test model identical to Sojourner used on earth was named Marie Curie. The third place prize went to Adam Sheedy, 16, of Round Rock, TX, who chose the late astronaut Judith Resnik as his namesake for the new rover.


  • Images of Sojouner approaching Yogi Rockmarker were used in the opening credits of the Star Trek: Enterprise science fiction television program, the first historical use in a science fiction film or television program of video taken on the surface of another planet.

See also


  1. Washington Post, "One Way or Another, Space Agency Will Hitch a Ride to Mars", 13 Nov 1993
  2. Windsocks on Mars, NASA
  3. Atmospheric and Meteorological Properties, NASA
  4. Golombek, M. et. al. 1997. Overview of the Mars Pathfinder Mission and Assesment of Landing Site Predictions. Science. Science: 278. p 1743-1748
  5. Smith, P. et. al. 1997. Results from the Mars Pathfinder Camera Science: 278. 1758-1765
  6. Hviid, S. et. al. 1997. Magnetic Properties Experiments on the Mars Pathfinder Lander: Preliminary Results. Science:278. 1768-1770.
  7. Bertelsen, P. et al. 2004. Magnetic Properties Experiements on the Mars Exploration rover Spirit at Gusev Crater. Science: 305. 827-829.
  8. Mars Pathfinder Science Results, NASA
  9. Max Bajracharya, Mark W. Maimone, and Daniel Helmick (2008) (Jet Propulsion Laboratory and California Institute of Technology); Autonomy for Mars rovers: past, present, and future; published in: Computer, a journal of the IEEE Computer Society, December 2008, Volume 41, Number 12, page 45, ISSN 0018-9162.
  11. Bruckner, J., G. Dreibus, R. Rieder, and H. Wanke. 2001. Revised Data of the Mars Pathfinder Alpha Proton X-ray spectrometer: Geochemical Behavior of Major and Minor Elements. Lunar and Planetary Science XXXII
  12. Mars probe may have spotted lost rover - space - 12 January 2007 - New Scientist Space
  13. NASA - Mars Pathfinder Landing Site and Surroundings

  • JPL Mars Pathfinder article
  • Mars Pathfinder Litograph Set, NASA. (1997)
  • Poster: Mars Pathfinder –Roving the Red Planet, NASA. (1998)
  • Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, Asif A. Siddiqi. Monographs in Aerospace History, #24. June 2002, NASA History Office.
  • "Return to Mars", article by William R. Newcott. National Geographic, pp. 2–29. Vol. 194, 2nd edition - August 1998.

  • "La misión Pathfinder –rebautizada Carl Sagan Memorial Station, en memoria del célebre astrónomo-, paso a paso todo Marte", de J. Roberto Mallo. Conozca Más, págs. 90-96. Edición número 106 - agosto de 1997.
  • "Un espía que anda por Marte", de Julio Guerrieri. Descubrir, págs. 80-83. Edición número 73 - agosto de 1997.
  • "Mars Pathfinder: el inicio de la conquista de Marte" EL Universo, Enciclopedia de la Astronomía y el Espacio, Editorial Planeta-De Agostini, págs. 58-60. Tomo 5. (1997)
  • Sojourner: An Insider's View of the Mars Pathfinder Mission, by Andrew Mishkin, Senior Systems Engineer, NASA Jet Propulsion Laboratory. ISBN 0-425-19199-0
  • Experiences with operations and autonomy of the Mars Pathfinder microrover, A. H. Mishkin, J. C. Morrison, T. T. Nguyen, H. W. Stone, B. K. Cooper and B. H. Wilcox. In Proceedings of the IEEE Aerospace Conference, Snowmass, CO 1998.

Bibliography on Mars

  • The New Solar System, J. Kelly Beatty, Carolyn Collins Petersen, Andrew Chaikin. Cambridge University Press; 4 edition (1998); ISBN 0-521-64587-5
  • The Surface of Mars, Michael H. Carr. Yale University Press, New Haven; 1 edition (1981); ISBN 0-300-02750-8, ISBN 0-300-03242-0
  • Exploring the Planets, Eric H. Christiansen, Kenneth W. Hamblin. Prentice-Hall, Englewood Cliffs, New Jersey; 2 edition (1995); ISBN 0-02-322421-5
  • The Search for Life on Mars: Evolution of an Idea, Henry S.F. Cooper. Holt, Rinehart, and Winston, New York (1980); ISBN 0-03-046166-9 (hardcover), ISBN 0-03-059818-4
  • Mars, Percival Lowell. Houghton, Mifflin, Boston, New York (1895). Kessinger Publishing (2004); ISBN 1-4191-3284-9
  • Journey Into Space: The First Thirty Years of Space Exploration, Bruce Murray. W.W. Norton, New York (1989); ISBN 0-393-02675-2 (hardcover), ISBN 0-393-30703-4
  • Planets & Perception: Telescopic Views and Interpretations, 1609-1909, William Sheehan. University of Arizona Press, Tucson (1988); ISBN 0-8165-1059-8
  • The Planet Mars: A History of Observation and Discovery, William Sheehan. University of Arizona Press, Tucson (1996); ISBN 0-8165-1640-5 (hardcover), ISBN 0-8165-1641-3
  • The Martian Landscape, Viking Lander Imaging Team. NASA SP-425 (1978)
  • Viking Orbiter Views of Mars, Viking Orbiter Imaging Team. NASA SP-441 (1980)
  • Mars Beckons, John Noble Wilford. ISBN 0-394-58359-0 (hardcover, 1 edition, 1990), ISBN 0-679-73531-3 (1991), ISBN 0-517-19803-7 (1997)

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