Space & Time


Latitude and Longitude

Force and Energy


Newton's theory of Gravity

The Age of the Universe

Special Relativity

General Relativity

The Big Bang



Mercury and Venus

Earth and Moon

Mars and the Asteroid Belt

Jupiter and Saturn

Uranus and Neptune

The Kuiper Belt and Oort Cloud

Pioneer and Voyager


Light & Matter

Atoms and Waves

Reflection, Refraction, and Diffraction

Newton's theory of Light

The Speed of Light

19th Century Wave Theories

19th Century Particle Theories

Spectral Lines

Early Quantum Mechanics

Thomson, Rutherford, and Atoms

The Quantum Atom

Matter Waves

Heisenberg's Uncertainty Principle

Schrödinger's Wave Equation

Quantum Entanglement

Schrödinger's Cat

Superconductors and Superfluids

Nuclear Physics

Fields and Forces

The Electromagnetic Force

The Strong Nuclear Force

The Weak Nuclear Force

Quantum Gravity

Mind & Multiverse

Socrates, Plato, and Aristotle


Locke and Berkeley

Hume and Kant

Material theories of the Mind

Material theories of the Mind vs. Descartes

Should we trust Theoretical Science?

Everett's Many Worlds Approach

The Preferred Basis Problem

The Problem of Probability

The Problem of Ockham's Razor

The Many Minds Approach

The Emerging Universe

Evidence of Parallel Worlds

Quantum Computers and Artificial Reality

Free will and Parallel-selves

Quantum Biology

Mars and the Asteroid Belt


Mars is the fourth closest planet to the Sun and takes almost 700 days to orbit. A day on Mars is less than an hour longer than a day on Earth. Mars is the next brightest object in the sky after Venus, and like Mercury and Venus, Mars is named after a Roman God, the god of war.

Mars is red for the same reason that rust is, 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.

There have been numerous successful and unsuccessful missions to Mars a list, including all spacecraft but Mars 2 and 3, is given in the image below.

In 1962, shortly after sending the first interplanetary spacecraft to Venus, Venera 1, the Soviet Union lunched the first probe to Mars, Mars 1.


Mars, a mosaic of images taken by the Mars Global Surveyor Orbiter. Image credit: NASA/JPL/MSSS.

Mars 1 had the same fate as Venera 1, and did not send back any data. Two more Soviet probes, Zond 1964A and Zond 2, were launched in 1964 and two more, dubbed M-69, in 1969, but these were all failures.

NASA's Mariner 3 and 4 were launched in 1964. Mariner 3 did not send back any useful information but Mariner 4 was successful, capturing the first ever images of another planet as it flew by. Mariner 5 went to Venus, but Mariner 6 and 7 were launched towards Mars in 1969, although they soon lost contact with Mariner 7.

Mars spacecraft

All spacecraft sent to Mars excluding Mars 2 and 3 (click to enlarge). Image credit: NASA, Roscosmos, ESA, JAXA, and Jason R. Davis.

Both NASA and the Soviet Union intended to send probes to Mars in 1971 - Mariner 8 and 9 and Cosmos 419 - but both Mariner 8 and Cosmos 419 failed to launch. The Soviet probes Mars 2 and 3 were also launched in 1971. Both were intended to land on the planet, although Mars 2 crashed it was the first human-made object to reach the Martian surface. Mars 3 landed successfully but only transmitted data for 14.5 seconds.

NASA's Mariner 9 was the first spacecraft to successfully orbit Mars in 1971. 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. It must also have contained a weather system, as there is evidence of rain or snow.

Mars 4, Mars 5, Mars 6, and Mars 7 were all launched in 1973. They were all successful except for Mars 7, which did not land on the planet due to a problem with altitude control.

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

Mars Landing sites

Mars landing sites. Image credit: NASA/AFP.

In 1996, NASA launched the Mars Global Surveyor (MGS) orbiter and Mars Pathfinder, which landed on the planet with its own miniature rover, Sojourner. Both missions were successful and the MGS began mapping Mars in 1999.

The Mars Pathfinder returned about 17,000 images, measured 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 Mars Odyssey orbiter was launched in 2001, and arrived just over 6 months later, in October of that year, finding evidence of frozen water on the surface.

Chasma Boreale

Chasma Boreale, a valley on Mars, a mosaic of images taken by Mars Odyssey. Image credit: NASA/JPL-Caltech/ASU.

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 confirmed the presence of frozen water and carbon dioxide at the poles.

NASA also launched probes to Mars in 2003, 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.

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.

NASA's Phoenix spacecraft was launched in 2007, and successfully landed in 2008. This was followed by the Mars Science Laboratory, with its own rover, Curiosity, in 2011. Curiosity landed in August 2012, and is still in operation. In 2013, NASA launched the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter, which began studying the Martian atmosphere in 2014 and is still in operation. 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 still in operation.

NASA plan to launch the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport lander (InSight) in 2016. This will land on Mars and study its geology. The Finnish Meteorological Institute plans to send a lander as part of its MetNet program, also in 2016. This will study the atmosphere and weather. The ESA and the Russian Federal Space Agency (Roscosmos) also plan to launch a mission to Mars in 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 will be launched in 2018. The Russian Federal Space Agency may send a lander, Mars-Grunt, in the mid-2020s. There are currently many potential amateur missions to Mars being planned including manned missions.

Frost on Mars

Frost on Mars around the Phoenix lander. Image credit: NASA/JPL-Caltech/University of Arizona/Texas A&M University.

Mars sand dunes

Sand dunes, images taken by the Mars Reconnaissance Orbiter. Image credit: NASA/JPL-Caltech/University of Arizona.

Mars sand dunes

Sand dunes, images taken by the Mars Reconnaissance Orbiter. Image credit: NASA/JPL-Caltech/University of Arizona.

Mars north pole

North pole, image taken by the Mars Reconnaissance Orbiter. Image credit: NASA/JPL/University of Arizona.

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 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 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 Fobos-Grunt, but it was unsuccessful. NASA is currently considering new missions to Mars' moons.


Phobos. Image credit: HiRISE, MRO, LPL (U. Arizona), NASA.


Deimos. Image credit: HiRISE, MRO, LPL (U. Arizona), NASA.

The Asteroid Belt

The asteroid belt is composed of boulders made of carbon, silicon, iron, and semi-precious stones, which orbit in the space between Mars and Jupiter. Asteroids are prevented from becoming gravitationally bound, and forming a planet, because of the strong gravitational pull of Jupiter and, individually, they are not massive enough to become spherical.

Over half of the mass of the asteroid belt is contained within four objects known as Ceres, Vesta, Pallas, and Hygiea. These are all over 400 km in diameter. The largest asteroid, Ceres, was discovered by Italian astronomer Giuseppe Piazzi in 1801. It is almost 1000 km in diameter and was accepted as a planet for almost 50 years, it is now designated a dwarf planet. NASA's Pioneer 10 probe was the first spacecraft to travel through the asteroid belt in 1972, later followed by Pioneer 11, Voyagers 1 and 2, and Ulysses. Ulysses was headed for Jupiter but the Pioneer and Voyager probes were headed even further - beyond the Solar System.


Ceres, mosaic of images taken by the Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.


Vesta, mosaic of images taken by the Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA.

The Galileo spacecraft imaged four asteroids between 1991 and 1997, while on its way to Jupiter. The Cassini spacecraft imaged two asteroids between 2000 and 2002, while headed for Saturn. The New Horizons spacecraft imaged another while heading for Pluto in 2006, and the Rosetta spacecraft imaged another in 2008, while headed for a comet.

Three spacecraft have been sent specifically to asteroids. The first was NASA's Near Earth Asteroid Rendezvous - Shoemaker (NEAR Shoemaker) which was launched in 1996. It landed on the asteroid Eros in 2001, after orbiting several times. The Japan Aerospace Exploration Agency (JAXA) launched the Hayabusa spacecraft to asteroid 25143 Itokawa, in 2003. It landed in 2005, and collected sampled that were returned to Earth in 2010. NASA's Dawn spacecraft was launched in 2007, and began to orbit Vesta in 2011. It left Vesta in September 2012, and is currently in orbit around Ceres.

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