Mars
For centuries people have wondered whether there is life on the planet Mars. The planet is relatively close to Earth and easy to observe through a telescope. This has led many to look for evidence of life. The idea has been a popular subject of literature and film, and the word martian today generally refers to any creature from outer space. Although studies have shown that there are no obvious signs of life, scientists have not yet been able to confirm whether microscopic life exists or has ever existed on Mars. The planet is named after the ancient Roman god of war because its red color resembles blood.
Mars is about 142 million miles (228 million kilometers) from the sun. This makes it the fourth planet from the sun. At about half the size of Earth, it is the third smallest planet in the solar system.
The surface of Mars is made up of rock and dust. Mars is like the Earth in that it has a dense core, a middle layer called a mantle, and a hard crust. Mars's biggest volcano, Olympus Mons, is also the largest known volcano in the solar system. It is 17 miles (27 kilometers) high. Olympus Mons is three times higher than Mount Everest in Asia, which is the highest point on Earth.
It is believed that water exists on Mars in the form of ice at its poles and vapor in its atmosphere. It is possible that there is also water below its surface. Pictures of Mars show that it has hundreds of channels that seemed to have been formed by flowing water. This seems to indicate that Mars had streams and shallow seas millions of years ago.
Mars has a thin atmosphere. It is mainly made up of carbon dioxide, with some nitrogen and argon. Small amounts of oxygen, carbon monoxide, and water vapor have also been found.
Like the Earth, Mars also has seasons. Spring and summer in the north last more than half the year. In the south the summer is shorter. Mars is much colder than Earth. The temperature at the Martian surface varies widely during the course of a day, from about −118 ° F (−83 ° C) just before dawn to about −28 ° F (−33 ° C) in the afternoon. Mars also has many global dust storms. Strong winds have moved the dust around the surface of Mars, and in some places, the surface rocks are completely covered with dust.
Like all planets, Mars has two types of motion, known as orbit and spin. Mars orbits the sun in 687 days. Therefore, one year on Mars is equal to 687 days. Mars spins on its axis at about the same rate as Earth. A Martian day therefore is about 24.6 hours. (For more information on orbit and spin, see planets.)
Mars has two satellites, or moons. They are named Phobos (Fear) and Deimos (Terror) after the sons of Ares, the Greek god of war. These satellites are irregular in shape, with cratered surfaces.
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Mars can be seen without the use of a telescope. Because of this, ancient people were able to observe the planet. In the early 1600s the Italian astronomer Galileo was the first person to use a telescope to make observations of Mars.
As better telescopes were developed in the 18th and 19th centuries scientists were able to study the planet in greater detail. In particular they began to question whether there was or had ever been life on Mars. In addition, scientists discovered Mars's satellites as well as detailed geographical information about Mars.
Technology in the later half of the 1900s made it possible to send unmanned spacecraft to the planet. From the 1960s to the 1980s, The United States and the Soviet Union sent many such spacecraft to Mars. Scientists were able to gather data in the form of photographs and other observations in these missions. This information helped scientists to understand more about the geography and atmosphere of the planet.
Beginning in the mid-1990s, missions to Mars became more elaborate. The United States National Aeronautics and Space Administration (NASA) sent the Mars Pathfinder to land on the planet and the Mars Global Surveyor to orbit Mars. They both arrived in 1997 and sent back information about the surface, interior, and atmosphere of Mars. In April 2001 NASA launched another orbiting satellite, the Mars Odyssey. The Odyssey gathered further information about the planet. It also helped NASA scientists communicate with two craft, called rovers, that were sent to Mars in 2003. The rovers—called Spirit and Opportunity—landed in late 2003 and early 2004. They were robots with wheels that allowed them to move around on the surface. The rovers performed experiments on the planet's soil and rocks and took many photographs.
