Mars

What is Mars?

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

The surface of Mars is dry, rocky, and mostly covered with iron-rich dust. There are low-lying plains in the northern hemisphere, but the southern hemisphere is dotted with impact craters. The ground is frozen; this permafrost extends for several kilometers.

The north and south poles of Mars are covered by ice caps composed of frozen carbon dioxide and water.

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 10²³ 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.

Mars’ Name and Symbol

Mars was named after the Roman god of war.