The Mars Pathfinder mission achieved its primary goal of validating the new technologies on the Pathfinder lander and rover, which were successful in transmitting data on the Martian atmosphere and on the planet’s surface geology and geochemistry, contributing to knowledge concerning whether Mars had been warmer and wetter in its past.
For the first several years of the 1990’s, the exploration of Mars encountered serious setbacks with the loss of the American Mars Observer mission in 1992 and, in 1996, the losses of the Russian Mars 96 mission and three American spacecraft either on the way to Mars or in orbit around it. Many countries had participated in these projects, and the hopes of scientists seeking knowledge of the Red Planet had been dashed. Around this time, National Aeronautics and Space Administration (NASA) administrator Daniel S. Goldin helped develop a new approach to Mars reconnaissance and research that would be “faster, better, and cheaper” than previous missions. Scientists and technicians designed the Mars Pathfinder, which was publicized as costing “only one dollar per American,” to test several new ideas, including a direct touchdown on Mars by means of air-bag-protected lander and rover vehicles. Unlike its failed predecessors, Mars Pathfinder proved to be a phenomenal success.
During the early phase of its three-year planning and development, Mars Pathfinder was known as the Mars Environmental Survey. Its basic idea of a stationary lander and a surface rover was the focus of scientific and technical personnel at the Jet Propulsion Laboratory
Without orbiting Mars, the spacecraft entered the planet’s atmosphere directly on July 4, 1997. During descent, the lander’s scientific instruments took atmospheric measurements. Pathfinder’s ablative heat shield slowed its rate of descent to about 830 miles per hour (370 meters per second), and a parachute slowed it even further, to about 160 miles per hour (68 meters per second). Twenty seconds later, the heat shield was released, and the lander and rover were prepared for initial contact with the surface when protective air bags surrounding them were inflated. At an altitude of 322 feet (98 meters), three solid rockets fired to slow the descent speed. The air-bag-encased lander and rover, traveling at 40 miles per hour (18 meters per second), hit the surface at nearly 3:00 in the morning Mars local solar time (a few minutes before 1:00
A little more than an hour after the landing, the air bags deflated and retracted, and the Pathfinder spacecraft opened its three triangular solar panels. After sunrise, the imaging system went into operation, taking pictures of the rover and the nearby Martian surface as well as a panoramic view of the location. Pathfinder then began transmitting to Earth the atmospheric and engineering data collected during entry and landing as well as the images it had collected. Scientists on Earth then received the information that the landing site was well within the planned landing site ellipse, which was near enough to the planet’s equator to provide sufficient sunlight for the solar panels. The landing site, which was named Carl Sagan Memorial Station
During Sol 1, Pathfinder’s first Martian day, JPL engineers recognized that one of the partially deflated air bags posed a problem for the upcoming deployment of the rover. They were able to use various commands to flatten the impeding air bag, and on Sol 2, the rover, which had been nicknamed Sojourner, exited the lander via a lowered ramp. Over the next several weeks, while the lander took pictures of the rover and the surrounding landscape, Sojourner, the first self-propelled vehicle to study a planet’s surface, made measurements of Martian rocks and soil.
The Pathfinder landed using a system of air bags that inflated about 100 meters above the planet’s surface and protected the rover upon impact.
Barnacle Bill was the first rock to be examined on Sol 3 (JPL scientists named prominent rocks for cartoon characters). It took the rover’s X-ray spectrometer about ten hours to complete a scan of this rock, which turned out to be similar to terrestrial andesite, a very common volcanic rock (its name derives from the Andes mountain range, where this silicate mineral is found). The rock called Yogi, the form and texture of which indicated former deposition by floodwater, was a basalt and more primitive than Barnacle Bill. The rock named Scooby Doo had white deposits, probably left by evaporating water. Several other rocks were studied, and most exhibited a high silicon content. In addition to volcanic rocks, Pathfinder discovered rocks similar to terrestrial sedimentary rocks, such as conglomerates, which may have formed in a watery matrix of sand, silt, and clay. In general, these rock analyses gave evidence of an ancient Mars that was more Earth-like than its highly arid present state.
The soils near the landing site, which contained rock fragments and meteoritic material, varied in color from red to dark gray. Chemically these soils, which were rich in silicon, sulfur, iron, and magnesium, were similar to the compositions found at the Viking 1 and Viking 2 sites, but, unlike the soils at the Viking sites, the Pathfinder soils provided evidence that water and wind erosion contributed to the current appearance of this section of the Martian surface. Pathfinder’s scientific instruments also studied the dust in the atmosphere by observing its deposition on magnetic targets on the spacecraft. This dust was highly magnetic, perhaps owing to the presence of maghemite, an iron oxide mineral.
Among the images captured by Pathfinder’s camera were vistas of distant hills. For example, Twin Peaks, a gentle ridge southwest of the lander, may have been deposited by the ancient flood that provided the “rock garden” explored by Sojourner. Further evidence of this ancient flood was provided by shallow grooves running parallel to the direction of the ancient water flow and the way that certain rocks were now piled against each other. However, bright patches on the flanks of these hills were most likely the result of drifting dust caused by recent windstorms.
During their activity on the planet, the Pathfinder’s instruments also made important meteorological observations. In general, the collected data revealed an extremely dry and dusty atmosphere, with patterns of pressure and temperature fluctuations. The pressure averaged about 6 millibars, about 1/170th of Earth’s value. The temperature varied from a maximum of 14 degrees Fahrenheit (-10 degrees Celsius) in the early afternoon to a minimum of -105 degrees Fahrenheit (-76 degrees Celsius) just before sunrise. Pressures and temperatures also varied with the height above the surface; for example, the air just a few feet above the ground was several degrees colder than the air at ground level. Dust devils, swirling columns of dust, were also a frequent occurrence, often caused by morning turbulence in the atmosphere.
These and other observations came to an end on September 27, 1997 (Sol 83), when flight operators at JPL failed to establish communications with the spacecraft, although they did not announce the end of the mission until November 4. The lander’s battery had been recharged many times, but after 40 Sols, the battery kept losing the capacity to keep the lander warm through the very cold Martian nights. After the public announcement, NASA’s flight team tried contacting Pathfinder through its main and its secondary transmitters, but all attempts failed. Nevertheless, the lander and rover had performed for much longer than the expected one month, and far more successfully.
Pathfinder was the most important mission to Mars since the Viking landings in 1976. Pathfinder cost only one-fifteenth of NASA’s expenditures for Viking, and it demonstrated that a relatively small and inexpensive planetary project could be completed successfully, even one that involved such new techniques as air-bag-protected touchdown of the spacecraft and automated obstacle avoidance by the rover. Pathfinder returned to Earth more than 2.5 billion bits of information, including more than 16,000 images from the lander and 550 images from the rover. By comparing the data from the Viking mission with those from Pathfinder, scientists were able to determine precisely how Mars wobbled as it rotated. In addition to the detailed information the mission provided on surface morphology, petrology, geology, geochemistry, and meteorology, Pathfinder helped to buttress the theories of planetary astronomers that, in its past, Mars had been warm and wet, with substantial liquid water existing on its surface beneath a thicker atmosphere than at present.
The Pathfinder mission was also very popular with the public. During the first month of the mission’s Martian explorations, the Pathfinder Web site generated 566 million hits. Some NASA officials were displeased by all the publicity surrounding Pathfinder, however, because they felt it diminished the prestige of the expensive space shuttle program. Indeed, scientists such as physicist Robert Park
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Croswell, Ken. Magnificent Mars. New York: Free Press, 2003. Provides an accessible and beautifully illustrated synthesis of the new knowledge acquired of Mars by various missions, including Pathfinder. Structured around the four ancient elements of earth, air, fire, and water. Includes glossary, suggestions for further reading, and index. -
Goldsmith, Donald. The Hunt for Life on Mars. New York: E. P. Dutton, 1997. Written before the Pathfinder mission, this work only anticipates what might be found to settle the centuries-old debate about whether life now exists or has ever existed on Mars. Includes glossary, suggestions for further reading, and index. -
Hartmann, William K. A Traveler’s Guide to Mars: The Mysterious Landscapes of the Red Planet. New York: Workman, 2003. Survey of the “new Mars” supplies for general readers an accurate, attractively illustrated, and comprehensive account of Mars as seen through the data collected by vicarious visitors such as Pathfinder. Includes glossary, bibliography, and index. -
Tokano, Tetsuya, ed. Water on Mars and Life. New York: Springer-Verlag, 2005. Collection of essays by experts in their respective fields surveys advances in research concerning water on Mars. Some authors explore the astrobiological implications of new data and discoveries. Includes maps, individual chapter bibliographies, and index.
Russians Launch the Salyut Space Station
Mars 2 Is the First Spacecraft to Impact Mars
Mariner 9 Is the First Spacecraft to Orbit Another Planet
Pioneer 10 Explores Jupiter and the Outer Planets
Skylab Inaugurates a New Era of Space Research
Mariner 10 Uses the Gravitational Pull of One Planet to Reach Another
Soviet Venera Spacecraft Transmit the First Pictures from the Surface of Venus
Viking Spacecraft Send Photographs to Earth from Mars
Voyagers 1 and 2 Explore the Outer Planets
First Ring Around Jupiter Is Discovered
Astronomers Discover an Unusual Ring System of Planet Neptune
Space Probes Begin Examination of Comet Halley