Chapter 19. The planet Mars

19.1 Characteristics of Mars

Mars is the fourth closest planet to the Sun and takes about 687 days to make one complete orbit. A day on Mars is less than an hour longer than a day on Earth.[1] 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.[2]

Photograph of Mars.

Figure 19.1
Image credit

Mars, a mosaic of images taken by the Mars Global Surveyor Orbiter.

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 volcano in the Solar System, Olympus Mons, and the largest canyon, Valles Marineris.[3]

Mars Fact Sheet[1]

Designation = Terrestrial (rocky) planet
Mass = 6.4×1023 kg (10.8% mass of Earth)
Radius = 3396 km (53.2% radius of Earth)
Density = 3933 kg/m3 (71.3% density of Earth)
Length of Day = 24.7 hours
Length of year = 687 Earth-days (1.9 Earth-years)
Days per year = 667.5 days on Mars per year on Mars
Distance from the Sun = 2.3×108 km (1.5 AU)
Orbital Velocity = 24.1 km/s
Orbital Eccentricity = 0.094
Obliquity (tilt) = 25.2°
Mean Temperature = -65 °C
Moons = 2 (Captured asteroids Phobos and Deimos)
Ring System = None

19.2 Mars’ moons

19.2.1 Phobos and Deimos

Mars has two moons, Phobos and Deimos, which were discovered by American astronomer Asaph Hall in 1877.[4] These are thought to be asteroids that were captured by Mars’ gravitational pull.[5]

Photograph of Mars’ moon Phobos.

Figure 19.2
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Photograph of Mars’ moon Deimos.

Figure 19.3
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Mariner 9 first photographed Phobos and Deimos in 1971. They were later photographed by Viking 1 and Viking 2, and many of the other missions bound for Mars, in the 1990s and 2000s. 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.

19.3 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 formed 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 somewhat 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. Mars 2 and Mars 3 were followed by Mars 4 - Mars 7, which were all launched in 1973, and were all at least partially successful.

NASA launched Viking 1 and Viking 2 in 1975. These both contained an orbiter and a lander, and were both successful. They returned the first colour photographs of Mars, and confirmed that Mars had once contained both rain and oceans.

Map of Mars, with landing sites marked.

Figure 19.4
Image credit

Mars landing sites (yellow).

The Soviet Union intended for Phobos 1 and Phobos 2 to pass Mars on the way to 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 orbit around the Earth.

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’s currently still in orbit around Mars, and still transmitting data back to Earth.

Photograph of a valley on Mars.

Figure 19.5
Image credit

Chasma Boreale, a valley on Mars, a mosaic of images taken by Mars Odyssey.

Japan’s Institute of Space and Astronautical Science (ISAS), now part of the Japan Aerospace Exploration Agency (JAXA), attempted to land the Nozomi spacecraft 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 naturalist 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’s 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’s 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 salt water on the sides of several craters.[6,7]

Dark streaks on the inside of a Crater on Mars.

Figure 19.6
Image credit

Dark streaks of flowing water on the side of the Garni Crater on Mars, image created using data from NASA’s Mars Reconnaissance Orbiter.

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 leave orbit around the Earth.

NASA has since sent two more probes to Mars, the Mars Science Laboratory and the MAVEN (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 begun studying the Martian atmosphere in 2014.

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.

Finally, the ESA and the Russian Federal Space Agency launched ExoMars in March 2016. This mission 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 2020.

A number of landers are also due to be launched in the near future. 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 about 2019. This will study the atmosphere and weather on Mars.

NASA and the ESA may launch the Mars Sample Return Mission in the mid-2020s, which would attempt to return a sample of Martian soil to Earth, and finally, the Russian Federal Space Agency may also send a lander, Mars-Grunt, in the mid-2020s.

There are currently also many private missions to Mars being planned including crewed missions.

19.3.1 Potential crewed missions to Mars

Europe, Russia, and China

In 2001, the ESA laid out a long-term plan that would eventually lead to a crewed mission to Mars, although it has no predicted launch date. The ESA teamed up with Russia and China to conduct the Mars-500 experiment from 2007 to 2011. This involved three crewmembers living in a simulated environment, first a simulated transit vehicle and then a Martian habitat, for up to 17 months at a time. It was considered a success.


NASA has been considering crewed missions to Mars since 1987, when they announced that they would aim to put humans on Mars by the 2020s. This goal was approved by President Ronald Reagan in 1988, and by President George H. W. Bush in 1989. These ideas were put aside in the 1990s, and human exploration was removed from NASA’s agenda in 1996. That same year, NASA engineer Robert Zubrin released The Case for Mars, a book based on a research paper he wrote with fellow engineer David Baker in 1990. Zubrin went on to form the Mars Society.

In 2004, President George W. Bush announced that human exploration was back on NASA’s agenda, suggesting that a lunar outpost may be developed in the 2020s. In 2010, President Barack Obama predicted that NASA would launch a crewed mission to an asteroid in 2025, and put people into orbit around Mars by the mid-2030s, with a crewed mission to the surface to follow.

The Mars Society

The Mars Society is a non-profit organisation based in the USA, with chapters around the world. It was founded by NASA engineer Robert Zubrin in 1998. The Mars Society’s proposal to eventually colonise Mars is based on a research paper Zubrin wrote with fellow engineer David Baker in 1990. They claim that a crewed mission to Mars, known as Mars Direct, is possible with current technology at a total cost of $30 billion. Members of the Mars Society Steering Committee include Buzz Aldrin, the second person to walk on the Moon, and Bruce Mackenzie, co-founder of the Mars Homestead Project.

The Mars Homestead Project

The Mars Homestead Project is run by non-profit organization The Mars Foundation, which is based in the USA. It intends to design and fund the development of a permanent settlement on Mars, but it has not yet set a launch date.


MarsDrive is another non-profit organization based in the USA, although it also has branches in the UK, Brazil, and Australia. Its goal is to involve the public in developing a plan to put a person on Mars.

Mars One

In 2012, Dutch engineer Bas Lansdorp and Dutch physicist Arno Wielders announced that their company, Mars One, will put four people on Mars by 2023.[8] They will grow their own food, create their own oxygen, and begin building larger living spaces for the four extra people who will join them every two years, creating the first human colony anywhere other than Earth. The catch is that they will have no way to come home.

Mars One claims that a suitable location will be chosen and supplies will be sent across in three missions, starting in 2020. The astronauts will embark on their seven month journey in 2026, and by the time they arrive, the living habitat will already be up and running.[9] Mars One estimate that it will cost at least $6 billion to put the first four people on Mars,[10] and they plan to raise this money by allowing the public to watch the astronauts for almost 24 hours a day. Since their announcement, Mars One has undergone a lot of criticism, with many suggesting that their plan is a hoax.[11]

Photograph of sand dunes on Mars.

Figure 19.7
Image credit

Sand dunes on Mars, images taken by the Mars Reconnaissance Orbiter.

Photograph of Mars’s north pole.

Figure 19.8
Image credit

Mars’ north pole, image taken by the Mars Reconnaissance Orbiter.

19.4 Colonising Mars

19.4.1 Physical requirements

A one-way crewed mission to Mars will require:[12]

  • A rocket and spacecraft for every mission.
  • A habitable space for people to live and work, with a functioning life support system.
  • Mars suits, so people can leave the habitat.
  • Mars Rovers, so they can travel further, and carry specimens and specialist equipment.
  • A communications system, so they can interact with people on Earth.

Many of these things will be relatively easy to make. Mars Suits are pressurised suits that supply the astronauts with oxygen, just like normal space suits. The Mars Rovers would be very similar to the Lunar Rovers that were taken to the Moon, and a communications system would consist of satellites conveying information at the speed of light, leading to a delay of between 3 and 20 minutes.[12]

The biggest challenges will probably be the rocket and spacecraft, and the life support system. The spacecraft will need to provide protection against the large doses of solar radiation that can occur sporadically, but this problem can be solved by building a reinforced shelter the astronauts can wait inside.[13]

Landing a spacecraft on Mars will be more difficult. Mars has an atmosphere, and so you cannot use the same method that NASA used to land people on the Moon. Previous missions to Mars have always used a parachute to slow their decent. Yet the atmosphere is so thin that it can only slow about a tonne to the right speed, and anything heavier is destroyed. It’s not yet known what the total weight of a crewed mission to Mars will be, but NASA estimates that you would need to land at least 40 tonnes worth of equipment at a time.[14]

This may be achieved with the Falcon Heavy launch system and the Dragon spacecraft, both designed by SpaceX. The Falcon Heavy is still in development. The Dragon spacecraft has already docked with the International Space Station, but it would still need to be modified in order to land on Mars. This possibility is currently being researched at NASA’s Ames Research Center.[15]

In 2011, researcher John Karcz advised NASA that the Dragon would be able to safely deliver up to a tonne without using a parachute, and that supersonic retro-propulsion would allow it to carry even more.[16] Retro-propulsion involves firing rockets in the direction the craft is travelling in, in order to slow it down. In order to land safely on Mars, this will need to be done while the spacecraft is still travelling faster than the speed of sound.

A self-sufficient habitat will also be difficult to construct on Mars. It’ll need to be covered in layers of sand in order to protect the astronauts from radiation, and incorporate a life support system that provides energy, food, water, and oxygen.

Mars One claims that their Mars Rovers will be able to travel in a 40 km radius, giving people an area of over 5000 square km to explore, an area about twice the size of Luxemburg. Mars One plan to cover up to 60% of this surface in solar panels in order to provide the habitat with electricity.

One problem with this is that Mars is dusty, and the whole of the planet’s surface can be covered in dust storms for weeks. During this time, far less light will get through, but Mars One claims there’ll still be enough to provide life support. When it’s safe to do so, people will have to use a Rover to blow the dust away.[17]

Inhabitants of Mars will have to grow their own food hydroponically, inside greenhouses. There is water within the Martian soil, which they can heat and then collect the evaporation. Part of this water can be used for drinking, cleaning, and feeding crops, and part can be used to produce oxygen. The rest of the artificial atmosphere could be filled with the inert gases nitrogen and argon, which can be extracted from Mars’ atmosphere.[18]

19.4.2 Mental requirements

In order for a crewed mission to Mars to succeed, people will have to cope with the psychological strains of both isolation and confinement. The trip there will take about 7 months. It will be stressful, as the astronauts will have very little personal space. There will be constant noise, they will be unable to shower, and they will have to live on minimal rations of food and water. They may have to spend days at a time inside the small refuge designed to protect them from solar radiation, and will have to exercise regularly to prevent osteoporosis.

Things will improve once they arrive in their living habitats. They will be able be able to wear normal clothes, shower, grow and cook fresh food, and begin work researching Mars. Although they’ll still not have much of a view, since the habitats must be covered in layers of sand to prevent radiation poisoning, and if anything does go wrong they will have to solve the problem themselves. Once there, the Earth will be just another star in the sky.

19.5 References

  1. NASA, Planetary Fact Sheet, Planetary Science - NASA.

  2. NASA, Mars Exploration Overview, NASA - Mars.

  3. NASA, Mars: Basic Facts, NASA Solar System Exploration.

  4. Hall, A., Monthly Notices of the Royal Astronomical Society 1878, 38, 205–209.

  5. Veverka, J., Thomas, P., Asteroids 1979, 1, 628–651.

  6. NASA, NASA Confirms Evidence That Liquid Water Flows on Today’s Mars, NASA, 2015.

  7. NASA, Dark, Recurring Streaks on Walls of Garni Crater on Mars, NASA, 2015.

  8. Mars One, Mars One will settle men on Mars in 2023, Mars One.

  9. Mars One, Roadmap, Mars One.

  10. Mars One, Will Mars One meet the exact time schedule?, Mars One.

  11. Holligan, A., Can the Dutch do reality TV in space?, BBC News, 2012.

  12. Mars One, The Technology, Mars One.

  13. NASA, Space Faring: The Radiation Challenge, NASA.

  14. Kinney, D. J., 49th AIAA Aerospace Sciences Meeting Orlando FL. 2011.

  15. Karcz, J., Karcz, J., Davis, S. M., Aftosmis, M. J., Allen, G. A., Bakhtian, N. M., Dyakonov, A. A., Edquist, K. T., Glass, B. J., Gonzales, A. A., Heldmann, J. L., Lemke, L. G., Red Dragon: Low-Cost Access to the Surface of Mars Using Commercial Capabilities, The NASA Advanced Supercomputing (NAS) Division, 2012.

  16. Karcz, J., Red Dragon: The Feasibility of a Dragon-derived Mars lander for scientific and human-precursor investigation, NASA Advisory Council Science Committee, 2011.

  17. Mars One, What are the risks of dust and sand on Mars?, Mars One.

  18. Mars One, Will the astronauts have enough water, food and oxygen?, Mars One.

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