The exploration of Mars has been an important part of the space exploration programss of the Soviet Union (later Russia), the United States, Europe, and Japan. Dozens of unmanned orbiters, landers, and rovers have been launched toward Mars since the 1960s aimed at gathering data on the red planet and answering questions about its past that may yield further insight into Earth's past, present, and future.
The exploration of Mars has come at a high financial cost with roughly two-thirds of all spacecraft destined for Mars failing in one manner or another before completing or even beginning their missions. Part of this high failure rate can be ascribed to technical incompetence, but enough have either failed or lost communications for no apparent reason that some researchers half-jokingly speak of an Earth-Mars "Bermuda Triangle" or of a Great Galactic Ghoul which subsists on a diet of Mars probes.
Mars has long been the subject of human fascination. Early telescopic observations revealed dry channels and depressions, possible evidence for running water or oceans in Mars' distant past. Polar ice caps, Olympus Mons, the solar system's tallest mountain, and Valles Marineris, the solar system's largest canyon system have only piqued further interest in the study and exploration of the red planet. Mars is a rocky planet like Earth that formed around the same time, yet it is only one-third the size and its surface is cold and desert-like. Among the questions asked by scientists are the following:
In order to understand the history of the robotic exploration of Mars it is important to note that launch windows occur at intervals of slightly over 2 years (the planet's synodic period).
Two Soviet flyby probes were launched towards Mars in October 1960, dubbed Mars 1960A and Mars 1960B, but both failed to reach Earth orbit. In 1962, three more Soviet probes failed -- two remaining in Earth orbit (Mars 1962A and Mars 1962B) and one losing communication with Earth en route to Mars (Mars 1). In 1964, the Soviet Zond 2 was another failed attempt to reach Mars.
In 1964 NASA's Jet Propulsion Laboratory made two attempts at reaching Mars as well. Mariner 3 and Mariner 4 were identical spacecraft designed to carry out the first flybys of Mars. Mariner 3 was launched on November 5, 1964, but the shroud encasing the spacecraft atop its rocket failed to open properly. Mariner 3 failed to reach Mars. Three weeks later, on November 28, 1964, Mariner 4 was launched successfully on an eight-month voyage to the red planet.
Mariner 4 flew past Mars on July 14, 1965, providing the first close-up photographs of another planet. The pictures, played back from a small tape recorder over a long period, showed lunar-type impact craters. Some of them seemed touched with frost in the chill Martian evening.
NASA continued the Mariner program with another pair of Mars flyby probes at the next launch window. These probes reached the planet in 1969. See Mariner 6 and 7 for details. During the following launch window the Mariner program again suffered the loss of one of a pair of probes. Mariner 9 successfully entered orbit about Mars, after the launch time failure of its sister ship, Mariner 8. When Mariner 9 reached Mars, it and two Soviet orbiters (Mars 2 and Mars 3, see Mars probe program below) found that a planet-wide dust storm was in progress. The mission controllers used the time spent waiting for the storm to clear to have the probe rendezvous with, and photograph, Phobos. When the storm cleared sufficiently for Mars' surface to be photographed by Mariner 9, the pictures returned represented a substantial advance over previous missions. These pictures were the first to offer evidence that liquid water might at one time have flowed on the planetary surface.
In 1971, shortly after Cosmos 419 failed to launch, the Soviet Union successfully sent Mars 2 and Mars 3, nearly a decade after the launch of Mars 1, all part of the Mars probe program. The Mars 2 and 3 probes each carried a lander, both arriving on Mars in 1971. The Mars 2 lander entered Mars' atmosphere at too steep an angle, causing it to crash, and the Mars 3 lander functioned for only 20 seconds after landing. They were the first human artifacts to touch down on Mars.
In 1973, the Soviets sent four more probes to Mars: the Mars 4 and Mars 5 orbiters and the Mars 6 and Mars 7 orbiter/lander combinations. Of the four, only Mars 5 succeeded; it transmitted 60 images before suffering a transmitter failure. Mars 6's lander transmitted data during descent but failed on impact. Mars 4 and 7 both missed the planet.
In 1976 the two Viking probes entered orbit about Mars and each released a lander module that made a successful soft landing on the planet's surface. The two missions returned the first color pictures and extensive scientific information. Measured temperatures at the landing sites ranged from 150 to 250 K, with a variation over a given day of 35 to 50 K. Seasonal dust storms, pressure changes, and movement of atmospheric gases between the polar caps were observed. A biology experiment produced no evidence of life at either landing site.
While searching for a suitable landing spot for Viking 2's lander, the Viking 1 orbiter photographed the landform that constitutes the so-called "Face on Mars" on July 25, 1976.
The Soviets went to Mars again in 1988 with the Phobos 1 and 2 probes to study the planet and its moons Phobos and Deimos. Phobos 1 lost contact on the way to Mars and Phobos 2 failed just before it was set to release two landers on Phobos' surface.
After the 1992 failure of NASA's Mars Observer orbiter, NASA retooled and launched Mars Global Surveyor. This mission was the first successful one to the red planet in two decades when it launched November 7, 1996, and entered orbit on September 12, 1997. After a year and a half trimming its orbit from a looping ellipse to a circular track around the planet, the spacecraft began its primary mapping mission in March 1999. It has observed the planet from a low-altitude, nearly polar orbit over the course of one complete Martian year, the equivalent of nearly two Earth years. Mars Global Surveyor completed its primary mission on January 31, 2001, and is now in an extended mission phase.
The mission has studied the entire Martian surface, atmosphere, and interior, and has returned more data about the red planet than all other Mars missions combined. This valuable data is archived at " class="external">http://wufs.wustl.edu/missions/mgs/mola/.
Among key scientific findings so far, Global Surveyor has taken pictures of gullies and debris flow features that suggest there may be current sources of liquid water, similar to an aquifer, at or near the surface of the planet. Magnetometer readings show that the planet's magnetic field is not globally generated in the planet's core, but is localized in particular areas of the crust. New temperature data and closeup images of the Martian moon Phobos show its surface is composed of powdery material at least 1 meter (3 feet) thick, caused by millions of years of meteoroid impacts. Data from the spacecraft's laser altimeter have given scientists their first 3-D views of Mars's north polar ice cap.
The Mars Pathfinder spacecraft, launched one month after Global Surveyor, landed on July 4, 1997. It carried a tiny remote-controlled rover called Sojourner, which traveled a few meters around the landing site, exploring the conditions and sampling rocks around it. The mission website was the most heavily-trafficked up to that time.
The "Ares Vallis" area, which is among the rockiest parts of Mars, as photographed by the Mars Pathfinder lander in its 1997 mission. The "twin peaks" are seen in the distance. ()
Following the success of Global Surveyor and Pathfinder, another spate of failures occurred in 1998 and 1999, with the Japanese Nozomi orbiter and NASA's Mars Climate Orbiter, Mars Polar Lander, and Deep Space 2 penetrators all suffering various fatal errors. Mars Climate Orbiter is infamous for mixing up the usage of imperial units with metric units while entering Mars' atmosphere.
In 2001 the run of bad luck ended when NASA's Mars Odyssey orbiter arrived. The probe's gamma ray spectrometer and neutron spectrometer have determined that there are vast deposits of water ice in the upper three meters of Mars's soil within 60° latitude of the south pole. Similar quantities of ice are expected to be present in the north polar region as well, but measurements will not be made until later in 2002.
On June 2, 2003, the European probe Mars Express set off from Baikonur Cosmodrome to Mars. The Mars Express craft consists of the Mars Express Orbiter and the lander Beagle 2. Although the landing probe was not designed to move, it carried a digging device and possibly the smallest mass spectrometer, as well as a range of other devices, on a robotic 'arm' in order to accurately analyse soil beneath the dusty surface. The orbiter entered Mars orbit on December 25, 2003, and Beagle 2 entered Mars' atmosphere the same day. Initial attempts to contact the lander failed.
On June 10, 2003, NASA's MER-A (Spirit) Mars Exploration Rover was launched. It successfully landed in Gusev Crater (believed once to have been a crater lake) on January 3, 2004. It will examine rock and soil for evidence of the area's history of water. On July 7, 2003, a second rover, MER-B (Opportunity) was launched. It is planned to land on January 25, 2004 in Meridiani Planum and will carry out similar geological work. The two names for these rovers were chosen by looking at essays from children around the United States. Both rovers are part of the Mars Exploration Rover Mission.
The center of the Gusev Crater, a relatively flat region of Mars, from the first color photograph by the Spirit rover while still on the lander in its 2004 mission. The depression at the right end of the photo was nicknamed "Sleepy Hollow" by mission scientists. ()
Many people, from Wernher Von Braun on, have long advocated a manned mission to Mars as the next logical step for a manned space program. As well as the undeniable romanticism of human exploration, such advocates believe that the amount of scientific work able to be performed in a human mission would be far superior than that possible with robotic explorers, thus making the large cost of a manned mission justifiable.
With current technology, a trip to Mars would be enormously expensive. Supplies and fuel would have to be prepared for a 2-3 year round trip and the spacecraft would have to be designed with at least partial shielding from intense solar radiation. A proposal called Mars Direct, forcefully advocated by Robert Zubrin of the Mars Society, is believed by many as the most practical and affordable plan for a manned Mars mission.
ESA, the European Space Agency, has the long-term vision of sending a human mission to Mars by 2030.
In the even longer term (centuries hence), some scientists believe Mars to be a good candidate for terraforming and human colonization, though other prominent skeptics (such as Robert Park) hotly dispute its practicality.
Dates listed are spacecraft launch dates.
Questions to explore
Mars with polar ice caps visible.Early flyby probes and orbiters
Early Soviet missions
Mariner program
Landers and later missions
This image was acquired at the Viking Lander 1 site with camera number 1. The large rock just left of center is about 2 meters wide. This rock was named "Big Joe" by the Viking scientists. The top of the rock is covered with red soil. Those portions of the rock not covered are similar in color to basaltic rocks on Earth. Therefore, this may be a fragment of a lava flow that was ejected by an impact crater. ()
Mars probe program
Viking program
Phobos program
Mars Global Surveyor
Mars Pathfinder
Spate of failures
Mars Odyssey
Mars Express
Mars Exploration Rovers
Manned missions
Timeline of Mars exploration
1960s
1970s
1980s
1990s
2000s
Scheduled/Planned
See also : Space colonization.