Mars is the fourth closest planet to the Sun and takes about 687 days to orbit. A day on Mars is less than an hour longer than a day on Earth. Mars is the next brightest natural object in the sky after Venus, and like Mercury and Venus, Mars is named after a Roman God, the god of war.
Mars, a mosaic of images taken by the Mars Global Surveyor Orbiter. Image credit: NASA/JPL/MSSS.
Mars is red for the same reason that rust is red, because the iron on its surface is oxidised. Mars has a thin atmosphere, mostly composed of carbon dioxide, and its surface is covered in craters, inactive volcanoes, valleys, deserts, and ice caps. Mars hosts the largest known mountain in the Solar System, Olympus Mons, and the largest canyon, Valles Marineris.
The planets, sizes approximately to scale. Image credit: Lunar and Planetary Institute.
The four inner planets to scale. Image credit: Lunar and Planetary Institute.
2.1 Phobos and Deimos ↑
Mars has two moons, Phobos and Deimos, which were discovered by American astronomer Asaph Hall in 1877. These are thought to be asteroids that were captured by Mars' gravitational pull. Phobos and Deimos were first photographed by Mariner 9 in 1971, and later by Viking 1 and Viking 2, and many of the other missions bound for Mars, in the 1990s and 2000s.
Phobos. Image credit: HiRISE, MRO, LPL (U. Arizona), NASA.
Deimos. Image credit: HiRISE, MRO, LPL (U. Arizona), NASA.
In 1988, the Soviet Union launched two probes to Phobos, Phobos 1 and Phobos 2. The first was lost, and the second only relayed a small amount of data. The Russian Space Agency launched a mission to Phobos in 2011, known as Phobos-Grunt, but it was unsuccessful. NASA is currently considering new missions to Mars' moons.
3. Missions to Mars ↑
There have been over 40 attempts to send spacecraft to Mars, about 25 of which have been successful. The Soviet Union made eight failed attempts to launch a probe to Mars in the 1960s, starting with Mars 1960A and Mars 1960B in 1960, and Mars 1962A, Mars 1962B, and Mars 1 in 1962. These were followed by Zond 2 in 1964, and Mars 1969A and Mars 1969B in 1969.
NASA made its first attempt to send a probe to Mars in 1964, with Mariner 3 and Mariner 4. Mariner 3 did not send back any useful information but Mariner 4 was successful, and produced the first images of another planet ever to be returned from deep space. Mariner 5 went to Venus, but Mariner 6 and Mariner 7 successfully flew past Mars in 1969.
Mariner 8 and Mariner 9 were due to launch in 1971, Mariner 8 failed, but the Mariner 9 mission was successful. It became the first spacecraft to orbit another planet, and remained in orbit for over a year. Mariner 9 found evidence for water on Mars, and showed that it had once contained rivers, which had led to the formation of large and complex canyons.
The Soviet Union launched 11 probes to Mars in the 1970s, starting with Cosmos 419, Mars 2 and Mars 3, which were launched in 1971. Cosmos 419 was a failure, but Mars 2 and Mars 3 were successful. It was planned for both Mars 2 and Mars 3 to land on the planet, and although Mars 2 crashed, it became the first human-made object to reach the Martian surface. Mars 3 landed successfully but only transmitted data for 14.5 seconds.
NASA launched Viking 1 and Viking 2 in 1975. These both contained an orbiter and a lander, and both were successful. They returned the first colour photographs of Mars, and confirmed that Mars had once contained both rain and oceans.
Mars landing sites (yellow). Image credit: modified from NASA/AFP.
The Soviet Union intended Phobos 1 and Phobos 2, to pass Mars on the way to its moon, Phobos. Both launched successfully in 1988, however they lost contact with Phobos 1 before it arrived. The Russian Federal Space Agency attempted to send a probe to Mars in 1996, Mars 96, but it failed to leave the Earth's orbit.
NASA made several failed attempts to send a probe to Mars in the 1990s, with the Mars Observer, Mars Climate Orbiter, and the Mars Polar Lander. They also had two successes, with the Mars Global Surveyor, and Mars Pathfinder, both of which launched in 1996.
The Mars Global Surveyor went into orbit around Mars, and continued to send back information until 2006. Mars Pathfinder landed on the planet with its own miniature Rover, Sojourner. It returned about 17,000 images, monitored the weather, and performed chemical analyses of rocks and soil. Data from both missions indicated that Mars may have once have been warm and wet, with flowing water.
NASA's 2001 Mars Odyssey orbiter was launched in 2001, and found evidence of frozen water on the Martian surface. It is currently still in orbit around Mars, and still transmitting data back to Earth
Chasma Boreale, a valley on Mars, a mosaic of images taken by Mars Odyssey. Image credit: NASA/JPL-Caltech/ASU.
Japan's Institute of Space and Astronautical Science (ISAS), now part of the Japan Aerospace Exploration Agency (JAXA), attempted to land Nozomi on Mars in 2003, however it failed to enter into orbit.
The European Space Agency (ESA) launched the Mars Express in 2003. This contained an orbiter and lander, Beagle 2 - named after British biologist Charles Darwin's HMS Beagle. The lander failed, but the orbiter was successful, and confirmed the presence of frozen water and carbon dioxide at the Martian poles. It is still in orbit around Mars, and still transmitting data back to Earth.
NASA also launched probes to Mars in 2003, which contained the Spirit and Opportunity Rovers. These both landed successfully, and the Opportunity Rover found rocks that are thought to have once been underwater, in a salty sea. Opportunity is still active, but NASA lost communication with Spirit in 2010.
NASA's Mars Reconnaissance Orbiter was launched in 2005, and attained Martian orbit in 2006. This mapped the terrain and weather in order to find suitable landing sites for future missions. It is currently still orbiting Mars, and transmitting data back to Earth. In 2015, data from the Mars Reconnaissance Orbiter was used to show that Mars currently contains flowing water.
NASA's Phoenix spacecraft launched in 2007, and successfully landed on Mars in 2008. The ESA's Rosetta spacecraft passed Mars in 2007, on its way to comet Churyumov-Gerasimenko, and NASA's Dawn spacecraft passed Mars in 2009, on its way to the asteroid belt. The China National Space Administration (CNSA) attempted to put Yinghuo-1 in orbit around Mars in 2011, however the mission failed to escape the Earth's orbit.
Frost on Mars around the Phoenix lander. Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University.
Sand dunes, images taken by the Mars Reconnaissance Orbiter. Image credit: NASA/JPL-Caltech/University of Arizona.
NASA has since sent two more probes to Mars, the Mars Science Laboratory and the MAVEN (the Mars Atmosphere and Volatile EvolutioN) orbiter. Both are still in operation. The Mars Science Laboratory launched in 2007, and landed its Rover, Curiosity, in 2012. MAVEN launched in 2013, and began studying the Martian atmosphere in 2014.
Finally, the Indian Space Research Organisation (ISRO) launched the Mars Orbiter Mission, also known as the Mangalyaan orbiter, in 2013. It began orbiting Mars the following year, and is also still in operation.
The ESA and the Russian Federal Space Agency also plan to launch a mission to Mars in March 2016. This mission is known as ExoMars, and will look for evidence of past or present life on Mars. They plan to extend the mission with a Rover, which is due to be launched in 2018.
NASA plan to launch InSight (the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport lander) in 2018. This will land on Mars and study its geology.
The Finnish Meteorological Institute plan to send a lander as part of its MetNet program in 2019. This will study the atmosphere and weather.
NASA and the ESA may launch the Mars Sample Return Mission in the mid-2020s. This would attempt to return a sample of Martian soil to Earth.‹ ›