The net Mars is an interesting and mysterious planet. It is often referred to as the “Red Planet.” The rocks, soil, and sky all have a red hue on account of rust. Mars is the fourth planet from the sun at about 141 million miles (228 million kilometers) and the last terrestrial planet from the Sun. Mars follows closely behind Earth but is comparatively smaller, with about half the diameter of Earth (6,794-km) and about one-tenth of Earth’s mass (6.419 x 1023 kg). Thus the force of gravity on Mars is about one-third of that on Earth. Mars is probably the planet we know the most about since it is so close to Earth, though what we know now is not even close to everything about the planet. As time goes on, our knowledge of this mysterious planet will expand.

Atmosphere
The atmosphere of Mars is quite different from that of Earth. It is composed primarily of carbon dioxide with small amounts of other gases. The six most common components of the atmosphere are Carbon Dioxide at 95.32%; Nitrogen at 2.7%; Argon at 1.6%; Oxygen at 0.13%; Water at 0.03%; and Neon at 0.00025 %. Martian air contains only about 1/1,000 as much water as our air, but even this small amount can condense out, forming clouds that rise high in the atmosphere or swirl around the slopes of towering volcanoes. Local patches of early morning fog can form in valleys. At the Viking Lander 2 site, a thin layer of water frost covered the ground each winter. There is evidence that in the past a denser Martian atmosphere may have allowed water to flow on the planet. Physical features closely resembling shorelines, gorges, riverbeds and islands suggest that great rivers once marked the planet.
Temperature
Mars is smaller and, because of its greater distance from the Sun, cooler than the eearth. It has seasons similar to Earth’s because the tilt of its rotational axis to the plane of its orbit about the Sun is about the same as earth’s. Interestingly, unlike Earth the significant elliptical shape of the Martian orbit means that the seasons on Mars are also affected by varying distance from the Sun. In the case of earth, because of its almost circular orbit, our seasons result simply from the tilt of the earth’s rotational axis.
The average recorded temperature on Mars is -81 F (-63 C) with a maximum temperature of 68 F (20 C) and a minimum of -220 F (-140 C). Barometric pressure varies at each landing site on a semiannual basis. Carbon dioxide, the major component of the atmosphere, freezes out to form an immense polar cap, alternately at each pole. The carbon dioxide forms a great cover of snow and then evaporates again with the coming of spring in each hemisphere.
The Interior
The current understanding of the interior of Mars suggests that it has a thin crust, similar to Earth’s, a mantle and a core. Using four criteria, the Martian core size and mass can be determined. However, only three out of the four are known and include the total mass, size of Mars, and the moment of inertia. Mass and size were determined accurately from early missions. The moment of inertia was determined from Viking lander and Pathfinder Doppler data. The fourth parameter, needed to complete the interior model, will be obtained from future spacecraft missions. With the three known parameters, the model is significantly confined. If the Martian core were composed of iron similar to Earth’s or meteorites thought to originate from Mars, then the minimum core radius would be about 1300 kilometers. If the core were made out of less-dense material such as a mixture of sulfur and iron, the maximum radius would probably be less than 2000 kilometers.
The Surface
Although it is much smaller, Mars does have the same surface land area as Earth. Other than Earth, Mars posses the most highly varied and interesting known terrain in our solar system. The surface of Mars is a very hostile place; however, it is more like Earth’s surface than any other planet in our solar system. Much of the Martian surface is rough and full of craters, but expansive flat plains and smooth hills can also be found. Unlike any other planet, there is a striking difference between the northern and southern hemispheres of Mars; one is extremely rough and old while the other is young and relatively smooth. The southern hemisphere is scattered with ancient craters of all sizes and is also elevated by a several kilometers, which creates a visible boundary. On the opposite end, the northern hemisphere consists of a wider variety of geological features, but is obviously smoother and much younger. There are large volcanoes, a great rift valley, and a variety of channels.
Volcanoes
Volcanism is a geological process that occurs on earth today, and has on many planetary bodies throughout the history of the solar system. No volcanism is occurring on the surface of Mars today. In the past, however, volcanism was one of the main forces creating and reshaping the surface of the planet. All of the rocks that have been observed by the Viking landers and the Mars Pathfinder Rover are generally agreed to be volcanic in origin. Tharsis is the largest volcanic region on Mars. It is approximately four thousand kilometers across, ten kilometers high, and contains twelve large volcanoes. The largest volcanoes in the Tharsis region are four shield volcanoes named Ascraeus Mons, Pavonis Mons, Arsia Mons, and Olympus Mons. The Tharsis Montes (Ascraeus, Pavonis, and Arsia) are located on the crest of the crustal bulge and their summits are about the same elevation as the summit of Olympus Mons, the largest of the Tharsis volcanoes. While not the largest of the Tharsis volcanoes, Arsis Mons has the largest caldera on Mars, having a diameter of one hundred twenty kilometers!
The largest of the volcanoes in the Tharsis region, as well as all known volcanoes in the solar system, is Olympus Mons. Olympus Mons is a shield volcano 624-km in diameter and 25-km high. A caldera 80-km wide is located at the summit of Olympus Mons. To compare, the largest volcano on earth is Mauna Loa. Mauna Loa is a shield volcano 10 km high and 120 km across. The volume of Olympus Mons is about one hundred times larger than that of Mauna Loa. In fact, the entire chain of Hawaiian Islands would fit inside Olympus Mons!
The main difference between the volcanoes on Mars and Earth is their size; volcanoes in the Tharsis region of Mars are ten to one hundred times larger than those anywhere on Earth. The lava flows on the Martian surface are observed to be much longer, probably a result of higher eruption rates and lower surface gravity. The less the gravitational pull, the higher volcanoes can grow without collapsing under their own weight.

Valleys
Valles Marineris, or Mariner Valley, is a vast canyon system that runs along the Martian equator just east of the Tharsis region. Valles Marineris is 4000-km long and reaches depths of up to 7 km! For comparison, the Grand Canyon in Arizona is about 800 km long and 1.6 km deep. In fact, the extent of Valles Marineris is as long as the United States and it spans about 20 percent of the entire distance around Mars! The canyon extends from the Noctis Labyrinthus region in the west to the chaotic terrain in the east. Most researchers agree that Valles Marineris is a large tectonic “crack” in the Martian crust, forming as the planet cooled, affected by the rising crust in the Tharsis region to the west, and then widened by erosional forces. However, near the eastern flanks of the rift there appear to be some channels that may have been formed by water.

The Tharsis bulge has a profound effect on the appearance, weather, and climate of Mars. It’s enormous mass may have dramatically changed the climate by changing the rotation of Mars.

Moons
Mars has two small moons: Phobos and Deimos. They were named after the sons of the Greek war god Ares, who was the counterpart to the Roman war god Mars. American astronomer Asaph Hall discovered both moons in 1877. The moons appear to have surface materials similar to many asteroids in the outer asteroid belt, which leads most scientists to believe that Phobos and Deimos are captured asteroids. Phobos’ mean distance from Mars is 9,377-km and Deimos’ is 23,436-km. The mass of Phobos is 10.8 x 1015 kg and the mass of Deimos is 1.8 x 1015 kg, which is quite small. This also suggests their being asteroids pulled into orbit around Mars.
Extraterrestrial Life?
Mars has been the subject of much discussion lately, mostly because of the bacteria-like material found in a piece of a meteorite from Mars in 1996. Before space exploration, Mars was considered the best candidate for harboring extraterrestrial life. Astronomers thought they saw straight lines crisscrossing its surface. This led to the popular belief that irrigation canals on the planet had been constructed by intelligent beings. Another reason for scientists to expect life on Mars had to do with the apparent seasonal color changes on the planet’s surface. This phenomenon led to speculation that conditions might support a bloom of Martian vegetation during the warmer months and cause plant life to become dormant during colder periods. In July of 1965, the Mariner 4 transmitted 22 close-up pictures of Mars. All that was revealed by these pictures was a surface containing many craters and naturally occurring channels, but no evidence of artificial canals or flowing water. Finally, in July and September 1976, Viking Landers 1 and 2 touched down on the surface of Mars. The three biology experiments aboard the landers discovered unexpected chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in the soil near the landing sites. According to mission biologists, Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil, and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil. The question of life on Mars at some time in the distant past remains open.
Mars is a planet full of mysteries just waiting to be discovered. It could perhaps hold the answer to questions we have been asking ourselves for years, such as the origin of life on earth. Is it possible that in the past there was water running on Mars, and when the end came, the beings there moved to earth? The answer is yes, for when we are dealing with space, anything is conceivable. We must keep our minds open to anything, for as we continue to search the space around us, we will continue to make new discoveries. The best way to say this is to use a quote from Star Trek, “Space: The final frontier.”