Mars - the Fourth Planet

Mars is the fourth planet from in our solar system and is the seventh largest. It is often referred to as the Red Planet. It is named after the Roman God of war Mars, which means Ares in Greek mythology. This paper will inform you about the physical characteristics of Mars, the exploration of Mars, the moons of Mars, and the possibility of life existing on Mars.

The atmosphere of Mars is very different than that of Earth. The atmosphere of Mars is mostly composed of carbon dioxide. Carbon dioxide makes up ninety-five percent of Mars's atmosphere. (Williams, 2005) Mars's atmosphere is also very thin. The average pressure on the surface of Mars only about seven millibars, which is less than one percent of the Earth's pressure. (Arnett, 2005) Though none of the other most common components of Mars's atmosphere accounts for more than three percent of it the other most common components of Mars's atmosphere are nitrogen, argon, oxygen, water, and neon. (Williams, 2005) The Mars atmosphere is so thin that it cannot hold heat. This causes the low temperatures on Mars because the atmosphere cannot sustain a strong greenhouse effect and it only raises the temperature about five degrees Kelvin. The average temperature on Mars is negative fifty-five degrees Celcius, which is about sixty-seven Faranheit. However, the maximum temperature recorded was 20o C, which is around 68o F. The lowest temperature was -140o C which is -220o F. (McKay, 1996) Mars is also famous for its windstorms. Sometimes one of its very strong wind and dust storms will engulf the entire planet for months. (Arnett, 2005) Mars's atmosphere is very unique in all sectors.

The terrain of Mars is one of the most varied and interesting of any of the terrestrial planets. The southern hemisphere of Mars is similar to our Moon's in that it is mostly ancient, cratered highlands. However the northern hemisphere consists of plains, which are much younger and also lower in elevation. (McKay, 1996) There are four main geological features on Mars. The most famous is probably Olympus Mons. Olympus Mons is an extinct shield volcano that rises more than twenty-four km and it is the tallest mountain in the solar system (Arnett, 2005). Mars is also home to the largest canyon in the solar system, Valles Marineris. Valles Marineris is 4,000 km long and seven km deep. (Sheehan, 1996) The other two main geological features of Mars are 1) Tharsis: a huge bulge on the Martian surface that is about ten km high and 4,000 km across and 2) Hellas Planitia: an impact crater in the southern hemisphere that is over six km deep and 2,000 km in diameter. (McKay, 1996) With all of those features, the terrain of Mars has to be one of the most interesting ones in the entire solar system.

Geologically, Mars is very similar to the Earth. Though Mars is much smaller than the Earth, its surface area is about the same as the land surface area as the Earth (Arnett, 2005). The surface of Mars is primarily composed of basalt and andesite rock, and it is covered in many places by meters of thick layers of dust as fine as talcum powder (Sheehan, 1996). Scientists only speculate about the interior of Mars, but based on inference from data about the surface and other statistics from the planet they concur that it most likely has a dense core about 3400 km in diameter, a molten, rocky mantle somewhat denser than the Earth's and a thin crust (McKay, 1996). Like Mercury and the Moon, Mars appears to lack active plate tectonics. There is no evidence of recent lateral motion of the surface such as the folded mountains that are so common on the Earth. There is also no evidence of volcanic activity. (Arnett, 2005) Even though there are no active plate tectonics now, observations of Mars's magnetic field has led scientists to believe that there were active plate tectonics long ago in Mars's past. In 1999 they discovered that parts of the planet's crust had been magnetized in alternating bands similar to the magnetic fields at the Mid-Atlantic Ridge Seafloor Spreading on Earth. (Sheehan, 1996)

Mars has two moons, Phobos and Deimos. Phobos is the largest and innermost of the two moons. It is closer to Mars than any other moon in the solar system is to its base planet. (Watkins, 2005) Phobos rises in the west and