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Where We’ve Been and Where We’re Going

Building on scientific discoveries and lessons learned from past and ongoing missions,

NASA's Mars Exploration Program is working over many years to establish a sustained

observational presence both around and on the surface of Mars. This includes orbiters

that view the planet from above and act as telecommunications relays; surface-based

mobile laboratories; robots that probe below the planet's surface; and, ultimately, mis-

sions that return soil and rock samples to Earth. With international cooperation, the

long-term program is guided by compelling questions that scientists are interested in

answering about Mars, developing technologies to make missions possible within

available resources. The program's strategy is to seek to uncover profound new

insights into Mars' past environments, the history of its rocks and interior, the roles and

abundance of water and, quite possibly, evidence of past and present life. 

As part of the NASA's Vision for Space Exploration, these missions of discovery fore-

see human exploration of the Moon, Mars and beyond in coming decades. 

The following are the most recently completed, ongoing and near-term future Mars

missions of exploration by NASA and its international partners: 

Mars Pathfinder (December 1996 - March 1998): The first completed mission in

NASA's Discovery Program of low-cost, rapidly developed planetary missions with

highly focused scientific goals, Mars Pathfinder far exceeded its expectations and out-

lived its primary design life. This lander, which released its Sojourner rover at the

Martian surface, returned 2.3 billion bits of information, including more than 17,000

images and more than 15 chemical analyses of rocks and soil and extensive data on

winds and other types of weather. Investigations carried out by instruments on both the

lander and the rover suggest that Mars had liquid water on its surface and a thicker

atmosphere. The lander and rover functioned far beyond their planned lifetimes (30

days for the lander and seven days for the rover), but eventually, after about three

months on the Martian surface, depletion of the lander's battery and a drop in the lan-

der's operating temperature are thought to have ended the mission. 

Mars Global Surveyor (November 1996 - present): During its primary mapping mis-

sion from March 1999 through January 2001, NASA's Mars Global Surveyor collected

more information than any other previous Mars mission. Today the orbiter continues to

gather data in a second extended mission. As of May 1, 2003, it has completed more

than 20,000 orbits of Mars and returned more than 137,000 images, 671 million laser-

altimeter shots and 151 million spectrometer measurements. Some of the mission's

most significant findings 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

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hematite, a mineral suggesting a wet environment when it was formed; and extensive

evidence for the role of dust in reshaping the recent Martian environment. Global

Surveyor provided valuable details for evaluating the risks and attractions of potential

landing sites for the Mars Exploration Rover missions, and served as a communica-

tions relay for the rovers during and after their landings. 

Mars Climate Orbiter and Mars Polar Lander (1998-99): These NASA spacecraft

were both lost upon Mars arrival. 

Mars Odyssey (April 2001 - present): This NASA orbiter's prime mapping mission

began in March 2002. Its suite of gamma-ray spectrometer instruments has provided

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. Odyssey's infrared camera system has also provided

detailed maps of minerals in rocks and soils. A layer of olivine-rich rock in one canyon

near Mars' equator suggests that site has been dry for a long time, since olivine is eas-

ily weathered by liquid water. Nighttime infrared imaging by Odyssey's camera system

provides information about how quickly or slowly surface features cool off after sunset,

which gives an indication of where the surface is rocky and where it is dusty.

Odyssey's observations helped evaluate potential landing sites for the Mars

Exploration Rovers, and relays via this orbiter have been the rovers' main way of send-

ing information to Earth. About 90 percent of data from the rovers has been relayed via

Odyssey, which passes over each rover twice a day. 

Mars Exploration Rover Spirit (June 2003 - present): Spirit and its twin,

Opportunity, are mobile robotic field geologists sent to examine geological clues about

the environmental history, particularly the history of water, at carefully selected sites.

Together, they make up NASA's Mars Exploration Rover Project. Spirit is exploring

inside Gusev Crater, a bowl 150 kilometers (95 miles) in diameter. Orbital images sug-

gest Gusev may have once held a lake fed by inflow from a large valley network that

channels into the crater from highlands to the south. Spirit landed in January 2003 in a

level plain pocked with small craters and strewn with loose rocks. The rover found that

the rocks on the plain are volcanic with slight alteration by exposure to water. By June

2003, Spirit had driven to a range of hills about 2.6 kilometers (1.6 miles) from the

landing site in a quest for exposed bedrock. Exploring in the hills since then, Spirit has

found an assortment of rocks and soils bearing evidence of extensive exposure to

water, including the iron-hydrogen-oxide mineral goethite and sulfate salts. 

Mars Exploration Rover Opportunity (July 2003 - present): This rover was sent to

a flat region named Meridiani Planum, where the spectrometer on Mars Global

Surveyor had discovered a large exposure of a type of hematite that usually, but not

always, forms in the presence of water. Opportunity landed inside a crater only 22

meters (72 feet) in diameter and immediately saw exposed bedrock in the crater's

inner slope. During the next few weeks, the rover's examination of that outcrop settled

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