Mars, the red planet, is the fourth planet from the sun and the most Earth-like planet in our solar system. It is about half the size of Earth and has a dry, rocky surface and a very thin atmosphere.

MARS' SURFACE

Olympus Mons, the largest volcano on Mars; it is perhaps the largest volcano in the Solar System. It is 17 miles (27 km) tall and over 320 miles (520 km) across. It is thought to be extinct.

Scientists have long thought that there is no liquid water on the surface of Mars now, but recent photos from Mars indicate that there might be some liquid water near the surface. The surface of Mars shows much evidence of the effects of ancient waterways upon the landscape; there are ancient, dry rivers and lakes complete with huge inflow and outflow channels. These channels were probably caused by catastrophic flooding that quickly eroded the landscape.

Scientists think that most of the water on Mars is frozen in the land (as permafrost) and frozen in the polar ice caps.

G. Schiaparelli was an Italian astronomer who first mapped Mars (in 1877) and brought attention to the network of "canali" (Italian for canals or channels) on Mars. These "canals" were later found to be dry and not to be canals at all. A Martian impact crater (Crater Schiaparelli, 461 km = 277 mi in diameter) and a hemisphere of Mars have been named after Schiaparelli.

SIZE
Mars is about 4,222 miles (6790 km) in diameter. This is 53% (a little over half) of the diameter of the Earth.

PLANETARY COMPOSITION
Crust and Surface: Mars' surface is composed mostly of iron-rich basaltic rock (an igneous rock). Mars has a thin crust, similar to Earth's.

Mantle: Silicate rock, probably hotter than the Earth's mantle at corresponding depths.

Core: The core is probably iron and sulphides and may have a radius of 800-1,500 miles (1,300-2,400 km). More will be known when data from future Mars missions arrives and is analyzed.

MASS AND GRAVITY
Mars' mass is about 6.42 x 10^23 kg. This is 1/9th of the mass of the Earth. A 100-pound person on Mars would weigh 38 pounds.

LENGTH OF A DAY AND YEAR ON MARS
Each day on Mars takes 1.03 Earth days (24.6 hours). A year on Mars takes 687 Earth days; it takes this long for Mars to orbit the sun once.

MARS' ORBIT
Mars is 1.524 times farther from than the sun than the Earth is. It averages 141.6 million miles (227.9 million km) from the sun. Its orbit is very elliptical; Mars has the highest orbital eccentricity of any planet in our Solar System except Pluto.

ATMOSPHERE
Mars has a very thin atmosphere. It consists of 95% carbon dioxide (CO₂), 3% nitrogen, and 1.6% argon (there is no oxygen). The atmospheric pressure is only a fraction of that on Earth (about 1% of Earth's atmospheric pressure at sea level), and it varies greatly throughout the year.

There are large stores of frozen carbon dioxide at the north and south poles. During the warm season in each hemisphere, the polar cap partly melts, releasing carbon dioxide. During the cold season in each hemisphere, the polar cap partly freezes, capturing atmospheric carbon dioxide.

The atmospheric pressure varies widely from season to season; the global atmospheric pressure on Mars is 25% different (there is less air, mostly carbon dioxide) during the (northern hemisphere) winter than during the summer. This is mostly due to Mars' highly eccentric orbit; Mars is about 20% closer to the Sun during the winter than during the summer. Because of this, the northern polar cap absorbs more carbon dioxide than the southern polar cap absorbs half a Martian year later.

Occasionally, there are clouds in Mars' atmosphere. Most of these clouds are composed of carbon dioxide ice crystals or, less frequently, of frozen water crystals.

There are a lot of fine dust particles suspended in Mars' atmosphere. These particles (which contain a lot of iron oxide) absorb blue light, so the sky appears to have little blue in it and is pink/yellow to butterscotch in color.

TEMPERATURE RANGE
Mars' surface temperature averages -81 °F (-63 °C). The temperature ranges from a high of 68° F(20° C) to a low of -220° F(-140° C). Mars is much colder than the Earth.

MARS' MOONS
Mars has 2 tiny moons, Phobos and Deimos. They were probably asteroids that were pulled into orbit around Mars.

SPACECRAFT VISITS
Mariner 4 was the first spacecraft to visit Mars (in 1965). Two Viking spacecraft landed in 1976. Mars Pathfinder landed on Mars on July 4, 1997, broadcasting photos. For more on the Mars missions, click here.

THE FACE ON MARS
This photograph of the Cydonia Mense region of Mars was taken by NASA's Mars Global Surveyor in 1998. It is a coincidental alignment of rocks and other geologic formations that happens to look like a human face from this angle.

DISCOVERY OF MARS
Mars has been known since ancient times.

THE MOONS OF MARS

Mars has two moon, Phobos and Deimos. They were discovered by the American astronomer Asaph Hall (1829-1907) in 1877.

PHOBOS Phobos (meaning "fear") is the larger of the two tiny moons of Mars. It is only 13.8 miles (22.2 km) across and has a mass of 1.08 x 1016. It orbits Mars at a mean distance of 5,600 miles (9,000 km). Its major feature is a large crater, named Stickney (Hall's wife's maiden name), which is 6.2 miles (10 km) wide. Phobos was discovered by astronomer Asaph Hall in 1877.

DEIMOS Deimos (meaning "terror") is the smaller of the two tiny moons of Mars. Deimos is only 7.8 miles (12.6 km) across and has a mass of 1.80 x 1015. It orbits at a mean distance of 14,300 miles (23,000 km) from Mars. It was discovered by A. Hall in 1877.

Missions to Mars

Mariner 4 was the first spacecraft to visit Mars in 1965. The first spacecraft orbited on Mars in 1971. The first spacecraft landed on Mars in 1976.

Missions	Date	Accomplishment
Mariner 4	1965	Fly-by mission: photos transmitted
Mariner 6 and 7	1969	Fly-by mission: atmosphere examined
Mariner 9	1971	Orbiter: First orbiter around another planet- mapping mission
Viking 1 and 2	1976	Lander: surface photos, soil biochemistry investigated. Orbiter: global mapping from orbit.
Phobos 2	1989	Orbiter: photos of Phobos
Mars Pathfinder	1997	Lander: (the first bouncing landing) plus "Sojourner" roving vehicle which performed rock analysis,
Mars Global Surveyor	1997	Orbiter: examine surface features, atmosphere, and magnetic properties.
Mars Climate Orbiter (NASA)	1998	Orbiter: study Martian weather and climate.
Mars Polar Lander (NASA)	1999	Lander: study soil and meteorology near Mars South Pole.
Mars Surveyor 2001 Orbiter (NASA)	March, 2001	Orbiter: study Mars from orbit, test aerocapture techniques, and act as a communications relay for the upcoming lander (see next entry).
Mars Surveyor 2001 Lander (NASA)	April, 2001	Lander: To bring the remote-controlled rover "Athena" to the surface, which will continue studying the Martian surface.
Mars Surveyor 2003 Orbiter (NASA)	2003-2004	Orbiter: study Mars from orbit, and serve as communications relay for the lander (see next entry)
Mars Surveyor 2003 Lander (NASA)	2003-2004	Lander: Brought the remote-controlled rover (Spirit) to the surface, which will continue studying the Martian surface.

Word Bank:

atmosphere south Deimos Sun permafrost

colder Roman ice temperature asteroids

moons day Earth-like craters fourth

Mars is the _____________________________ planet from the sun and the most _____________________________ planet in our Solar System. Mars was named after the _____________________________ god of war. Mars is about 4,222 miles (6790 km) in diameter. This is 53% (a little over half) of the diameter of the Earth. Mars' mass is about 6.42 x 10²³ kg. This is 1/9th of the mass of the Earth. A 100-pound person on Mars would weigh 38 pounds.