Mass:641,693,000,000,000 billion kg (0.107 x Earth)
Equatorial Diameter:6,805 km
Polar Diameter:6,755 km
Equatorial Circumference:21,297 km
Known Moons:2
Notable Moons:Phobos & Deimos
Orbit Distance:227,943,824 km (1.38 AU)
Orbit Period:686.98 Earth days (1.88 Earth years)
Surface Temperature:-87 to -5 °C
First Record:2nd Millenium BC
Recorded By:Egyptian astronomers

Mars is the fourth planet from the Sun and last of the terrestrial planets. Like the rest of the planets in the solar system (except Earth), Mars is named after a mythological figure – the Roman god of war. In addition to its official name, Mars is sometimes called the Red Planet because of the brownish-red color of its surface. Mars is the second smallest planet in the solar system behind Mercury.


Side by side comparison of the size of Mars vs Earth
Side by side comparison of the size of Mars vs Earth


  • Mars is the fourth planet from the Sun and last of the terrestrial planets and is around 227,940,000 km from the Sun.
  • The planet is named after Mars, the Roman god of war. It was known to the ancient Greeks as Ares, their god of war. This is thought to be because of the blood-red color of the planet which was also used by other ancient cultures. Chinese astronomers call Mars the “fire star” while ancient Egyptian priests called it “Her Desher” meaning “the red one”.
  • The landmass of Mars and Earth is very similar. Despite Mars being just 15% the volume and 10% the mass of Earth, it actually has a similar landmass because water covers about 70% of Earth’s surface. The surface gravity of Mars is about 37% the gravity found on Earth. This means that on Mars you could in theory jump 3x higher than you could on Earth.
  • Only 16 of the 39 Mars missions have been successful. Beginning with the USSR’s Marsnik 1 which was launched in 1960, 39 orbiters, landers and rovers have been to Mars but only 16 of those missions were a success. In 2016, Europe’s Exobiology on Mars program will search the planet for signs of Martian life as well as study the surface and terrain of the planet and map potential environmental hazards to future manned missions to Mars.
  • Pieces of Mars have been found on Earth. It is believed that trace amounts of the Martian atmosphere were within meteorites that the planet ejected. These meteorites then orbited the solar system for millions of years amongst the other objects and solar debris before eventually entering the Earth’s atmosphere and crashing to the ground. The study of this material has allowed scientists to discover more about Mars before launching space missions.
  • Mars was once believed to be home to intelligent life. This came from the discovery of lines or grooves in the surface called canali by Italian astronomer Giovanni Schiaparelli. He believed that these were not naturally occurring and were proof of intelligent life. However, these were later shown to be an optical illusion.
  • The tallest mountain known in the solar system is on Mars. Olympus Mons is a 21 km high and 600 km diameter shield volcano that was formed billions of years ago. Scientists have found a lot of recent evidence of volcanic lava which suggests Olympus Mons may still be active. It is the second highest mountain in the entire solar system, topped only by the Rheasilvia central peak on the asteroid Vesta, which is 22 km high.
  • Mars experiences huge dust storms – the largest in our solar system. This is due to the elliptical shape of the planet’s orbit path around the Sun. The orbit path is more elongated than many of the other planets and this oval shaped orbit results in fierce dust storms that cover the entire planet and can last for many months.
  • The Sun looks about half its size half it does from Earth when seen from Mars.When Mars is closest to the Sun in its orbit the southern hemisphere points toward the Sun and this causes a very short but fiercely hot summer. In the north it experiences a brief but cold winter. When the planet is farthest from the Sun, Mars experiences a long and mild summer because the northern hemisphere points toward the Sun. This is compared with a cold and lengthy winter in the south.
  • With the exception of Earth, Mars is the most hospitable to life – a number of space missions are planning for the next decade the further increase our understanding of Mars and when it has the potential for extraterrestrial life, as well as whether it may be a viable planet for a colony.
  • Martians, also known as extraterrestrials from Mars, are a common character in science fiction books and movies. This makes Mars one of the most popular and talked about planets in the solar system.
  • It takes Mars 687 Earth days to orbit the Sun with its orbit radius of 227,840,000 km.
  • Mars is the only other planet besides Earth that has polar ice caps. The northern cap is called the Planum Boreum, with Planum Australe in the south. Water ice has also been found under the Martian ice caps.
  • Mars has seasons like Earth, but they last twice as long. This is because Mars is tilted on its axis by about 25.19 degrees, which is similar to the axial tilt of the Earth (22.5 degrees).
  • The orbit of Mars is the most eccentric of the eight planets. This means it is the least circular orbit path of the planets.
  • The two moons of Mars, Phobos and Deimos, were written about in the book ‘Gulliver’s Travels’ by author Jonathan Swift – 151 years before they were discovered.
  • Mars does not have a magnetic field – although there are some scientists that believe it did have a magnetic field somewhere around 4 billion years ago.


It was believed life existed on Mars for much of the nineteenth century. The reason behind this belief was part mistake and part imagination. In 1877, the astronomer Giovanni Schiaparelliobserved what he believed to be straight lines on Mars’ surface. As others noticed these lines, some suggested that they were too straight and could only be the work of intelligent life. The popular conclusion as to the nature of these lines was that they were canals constructed for irrigation purposes. However, with the development of more powerful telescopes in the early twentieth century, astronomers were able to view the Martian surface more clearly and determine that these straight lines were merely an optical illusion. As a result, the earlier claims of life on Mars were without evidence and, therefore, discarded.

The large amount of science fiction written during the twentieth century was a direct outgrowth of the belief that Mars possessed life. From little green men to death rays, Martians were the focus of many television and radio programs, comic books, movies, and novels.

Although the discovery of Martian life in the eighteenth century eventually proved to be false, Mars is nonetheless the planet most hospitable for life other than the Earth. As such, recent planetary missions have tried to determine if even the most basic of life exists on the planet’s surface. The Viking mission in the 1970s conducted experiments on the Martian soil in hopes of detecting microorganisms. While it was initially believed that the formation of compounds during the experiments were a result of biological agents, it has since been determined that these compounds can be created without biological mechanisms.

Even though the results lean toward the absence of life on Mars, scientists have speculated that conditions are right for life to exist beneath the planet’s surface. Future planetary missions scheduled to test the possibility of past and present life include the Mars Science Laboratoryand ExoMars missions.


The composition of Mars’ atmosphere is extremely similar to Venus’, one of the least hospitable atmospheres in all of the Solar System. The main component in both atmospheres is carbon dioxide (95% for Mars, 97% for Venus), yet a runaway greenhouse effect has taken hold of Venus, producing temperatures in excess of 480° C, while temperatures on Mars never exceed 20° C. Thus, something other than the composition is at work. The huge difference lies in the density of the two atmospheres. Whereas Venus’ atmosphere is exceedingly thick, Mars’ is quite thin. Simply put, Mars would resemble Venus if it possessed a thicker atmosphere.

Additionally, with such a thin atmosphere, the resulting atmospheric pressure is only about 1% of that found at sea level on Earth. That is the equivalent pressure found at 35 km above the Earth’s surface.

One of the long standing areas of research regarding the Martian atmosphere is its impact on the presence of liquid water. What the research has shown is that even though the polar caps possess frozen water and the air contains water vapor— a result of the freezing temperatures and low pressure caused by the weak atmosphere— is not possible for liquid water to exist on the planet’s surface. However, evidence provided by planetary missions suggests liquid water does exist one meter below the planet’s surface.

Surprisingly, despite the thin atmosphere, Mars experiences weather patterns. The primary form of this weather consists of winds, with other manifestations that include dust storms, frost, and fog. As a result of this weather, some erosion has been seen to take place at particular locations on the planet’s surface.

As a final note on the Martian atmosphere, leading theories claim that it may have once been dense enough to support large oceans of water. However, through some means in the planet’s past the atmosphere was drastically altered. One popular explanation for this change is that Mars was struck by a large body and in the process a large portion of its atmosphere was ejected into space.


The surface of Mars can be separated into two broad features, which, coincidentally, are divided by the planet’s hemisphere. The northern hemisphere is seen to be relatively smooth with few craters, whereas the southern hemisphere is an area of highlands that are more heavily cratered than the northern plains. Other than topographical differences, the distinguishing feature of the two regions appears to be geological activity, with the northen plains being much more active.

The Martian surface is home to both the largest known volcano, Olympus Mons, and largest known canyon, Valles Marineris, in the Solar System. With a height of 25 km and a base diameter of 600 km, Olympus Mons is three times the height of Mt. Everest, the tallest mountain on the Earth. Valles Marineris is 4,000 km long, 200 km wide, and almost 7 km deep. To put the shear magnitude of its size into perspective, Valles Marineris would stretch from the East to West coast of the United States.

Perhaps the most significant discovery regarding the Martian surface was the presence of channels. What is so meaningful about these channels is that they appear to have been created by running water, and thus providing evidence to support the theory that Mars could have been much more similar to the Earth at one time.

A surface feature that has remained in popular culture since its image surfaced is the “Face on Mars.” When this photograph was captured by the Viking I spacecraft in 1976, many took it to be proof that alien life existed on Mars. However, subsequent images showed that lighting (and a little imagination) are what brought life to the formation.


Similar to the other terrestrial planets, Mars’ interior is divided into three layers: a crust, mantle, and core.

Although precise measurements cannot be made, scientists can make predictions as to the thickness of the planet’s crust based on the depth of Valles Marineris. Such a deep, extensive valley system, located in the southern hemisphere, could not be present unless the crust there is significantly thicker than the Earth’s. Estimates put its thickness in the northern hemisphere at 35 km, and 80 km in the southern hemisphere.

Mercury’s core is believed to be approximately 3,000 km in diameter and composed primarily of iron. There is a significant amount of research being conducted to determine whether or not Mars’ core is solid. Some scientists point to the lack of a significant magnetic field as an indication that the core is solid. However, within the past decade much data has been gathered to indicate that the core is at least partially liquid. With the discovery of magnetized rocks on the planet’s surface, it appears, at the very least, that Mars did possess a liquid core at some point in its history.


The orbit of Mars is noteworthy for three reasons. First, its eccentricity is second largest among all the planets, smaller only than Mercury’s. As a result of this more elliptical orbit, Mars’ perihelion of 2.07 x 108 km is much larger than its aphelion of 2.49 x 108 km. Second, evidence suggests that this high degree of eccentricity has not always been present, and it may have been less than the Earth’s at some point in Mars’ history. The cause for this change is attributed to the gravitational forces exerted upon Mars by neighboring planets. Third, of all the terrestrial planets, Mars is the only one having a year that lasts longer than the Earth’s. This, of course, is due to its orbital distance. One Martian year is equal to almost 686 Earth days.

It takes Mars about 24 hours 40 minutes to complete one full rotation, easily making the Martian day the closest in length to an Earth day.

At roughly 25°, Mars’ axial tilt is yet another similarity the planet shares with Earth. What this means is Mars actually experiences seasons like those on Earth, though each is substantially longer because of the orbital distance of Mars. Unlike the Earth, however, Mars’ two hemispheres experience quite different temepratures for each season. This is due to the much larger eccentricity of the planet’s orbit.

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