At the same time as the successes of the United States’ Project Apollo, which ultimately sent astronauts to the Moon were mounting, both the U.S. and the Soviet Union developed a large suite of robotic space probes that traveled to other planets. The Soviets had a series of failed missions to Mars, but the Americans sent missions that successfully flew past, orbited, and eventually landed on Mars.
Despite a number of attempts in the 1960s, the Soviets didn’t have any luck with an operational Mars probe until the 1970s. Even then, the few Soviet spacecraft that were modest successes couldn’t match the data quality and quantity from contemporary NASA missions.
Early planetary exploration didn’t belong solely to the Soviet Union. American planetary research started with the Mariner Program, the United States’ first long-running interplanetary spacecraft program, which was intended to start exploring the strange new worlds of Mercury, Mars, and Venus. This program consisted of ten space missions, seven of which were successes
NASA’s Viking missions to Mars in the 1970s provided a wealth of data from two orbiters and two landers. Not only that, but these landers actually performed the first search for life on another planet.
The scientific goal of the Viking missions was clear: Study the biological, physical, chemical, and other properties of Mars’s atmosphere and surface in an effort to better understand the planet and its potential to support life. Each Viking lander housed numerous instruments, including cameras, sample-collection devices, and temperature and wind sensors, to help it fulfill this goal. None of these tests proved conclusively that there was life (as we know it, at least) on Mars.
At the dawn of the Space Age, science fiction blended with science fact to produce a view of the solar system that included life on other planets. Although the first missions to the Moon, Mars, and Venus revealed harsh conditions that seemed unlikely to support life as we know it, scientists knew life could still exist elsewhere in the solar system. In 1966, the U.S. and several other nations signed a space exploration treaty, part of which requires that nations protect other planets and the Earth from contamination due to space exploration.
Robotic exploration of Mars took a long hiatus following the failure of NASA’s 1976 Viking missions to detect life, although not for lack of trying. The Soviet Union’s Phobos spacecraft failed due to computer glitches in the late 1980s, and the United States’ Mars Observer spacecraft was lost in the early 1990s, further depressing the status of NASA’s planetary exploration program.
Renewed exploration of the Red Planet didn’t start out well. The first post-Viking Mars missions were a pair of ambitious spacecraft developed by the Soviet Union. As part of the Phobos program, the Soviets sent a pair of robotic spacecraft, Phobos 1 and Phobos 2, to Mars to study both the planet itself and its two small moons, Phobos and Deimos. The missions launched a few days apart in July 1988. Phobos 1 never made it into Mars orbit. Phobos 2 transmitted some 40 images before contact was lost.
NASA’s Mars Observer was supposed to study the surface material of Mars in depth, in addition to determining the nature of Mars’s gravitational and magnetic fields and obtaining details on Martian weather and atmosphere. It was also meant to be the first of a series of missions, much like the Mariner and Pioneer mission series of two decades earlier. The Observer missions were intended to study the inner solar system, but Mars Observer was the only one of these missions to launch. The spacecraft was lost in transit towards Mars.
As part of NASA’s Discovery Program, the Mars Pathfinder mission was seen mainly as a testbed for trying out technologies, innovations, and equipment intended for later missions. It was also responsible for conducting experiments designed to reveal more about the structure, topography, and composition of the Martian surface.
The Mars Global Surveyor (MGS) mission, a separate mission from the Discovery Program, actually marked the beginning of the United States’ return to Mars because it launched a month before the Mars Pathfinder mission. However, it arrived in orbit around the Red Planet later than Pathfinder. The MGS mission had several major scientific goals: study and map the surface characteristics of Mars, discover the true shape of the planet, plus details on its topography, find out about Mars’s magnetic field, record weather patterns and atmospheric details.
In 1996, a Russian Mars mission, called Mars 96, was resurrected. Its goals were to explore the surface of Mars and create maps of the Red Planet’s structure, topography, and composition. Mars 96 also was charged with studying Mars’s magnetic field and examining gamma rays and other phenomena on its way to the planet. Although liftoff initially succeeded, the spacecraft’s launch vehicle failed in its final stage, leaving Mars 96 unable to leave Earth orbit.
Publication of scientific papers does not often generate headlines. But when news leaked that the August 16, 1996, issue of the prestigious journal Science would contain a paper offering proof of life on Mars, NASA Administrator Dan Goldin had to schedule a press conference to stop wild speculations by the media. “I want everyone to understand that we are not talking about ‘little green men,’ ” he said in announcing the press conference. “These are extremely small single-cell structures that somewhat resemble bacteria on Earth.”
The Mars Pathfinder and Mars Global Surveyor missions set the stage for what was to be an ambitious program of Mars exploration by NASA. However, that program was derailed almost before it began thanks to two mission failures. The Mars Climate Orbiter was part of a two-spacecraft program with the Mars Polar Lander. These two Mars missions were intended to provide detailed studies of the weather, atmosphere, water, and general climate on Mars, but neither fulfilled its goals. The loss of Mars Climate Orbiter and Mars Polar Lander resulted in severe setbacks for the just-rebounding NASA Mars exploration program.
Mars Odyssey, which reached Mars orbit in 2001, was the first robotic spacecraft to successfully reach Mars in the 21st century. Its purpose? To start looking for evidence of volcanic activity and water on the surface of Mars. Perhaps the spacecraft’s most significant finding is the existence of places on the Martian surface that may hold chloride minerals such as salt. Additionally, data gathered by Mars Odyssey has revealed concentrations of hydrogen that are thought to indicate near-surface water, which could indicate the more-recent presence of habitable locations on the Red Planet.
In 2003, the European Space Agency (ESA) got into the act of Mars exploration with its ambitious Mars Express mission. Intended to send both a lander and an orbiter to study the geology and biology of Mars, Mars Express was also charged with taking climatic and atmospheric measurements and investigating the Martian surface and subsurface. Despite the failure of its lander, Beagle 2 to land on Mars, the Mars Express orbiter reached orbit successfully and has been returning valuable scientific images and measurements.
The ability to move around on the surface of Mars has revolutionized people’s understanding of the wide variety of environments present on the Red Planet. Lessons learned from the tiny yet successful Sojourner rover helped NASA engineers design the two Mars Exploration Rovers: Spirit and Opportunity. These rovers are fully mobile, solar-powered labs capable of sending their data to an orbiting spacecraft for relay back to Earth. If necessary, they can even contact Earth directly from the Martian surface. The initial goals of the MER mission were to explore and start defining the surface characteristics of Mars.
Many images of Mars have been taken from orbit, but none boast the impressive degree of detail provided by the images taken from Mars Reconnaissance Orbiter. MRO’s mission goals were to view the surface of Mars at as high a resolution as possible from orbit to help NASA better understand how the landing sites for the rovers Spirit and Opportunity fit into the overall picture of Mars (see the previous section for details on the rovers), as well as to help select sites to which future missions could be directed.
The Phoenix Mars Lander was a robotic spacecraft sent to Mars to find definitive evidence of water. And find water it did! In June 2008, the lander dug a trench that was filled with a bright material scientists thought could’ve been ice. Several days later, the bright clumps had vaporized, suggesting that they were probably water ice. Additional evidence of water was gleaned from water vapor measurements sent back in late July 2008. All previous Mars landers have set down near the Martian equator, but Phoenix was targeted for terrain near the North Pole.