Mars is the fourth planet in order from the sun. The name of this planet comes from the Roman god of war - Mars. The ancients called it as such because the planet observed from Earth has rusty red hue which was associated with the conflagration of war. From there we got a term "Red Planet". Hue is follows that the planet's surface contains iron oxides. Mars is the inner planet with a thin atmosphere and the surface dotted with impact craters. Just like a Moon's surface. There are also other types of terrain there, similar to Earth: volcanoes, valleys, deserts and polar ice caps.
Mars rotates on it's axis like Earth. Martian day is a bit longer than Earth day. It lasts 24.6 h. On Mars we have seasons analogous to Earth but their length is twice which is caused by a longer circulation around the Sun and fact that perpendicular to the axis of rotation equatorial plane is inclined to the ecliptic plane at an angle of 24 degrees. Mars is smaller than Earth, it's equatorial radius is 3397 km long. The planet's mass is only 0.1 of the Blue Planet and is 3 million times smaller than mass of Sun. The average density of matter in the red planet is less than the other planets of the Earth Group and it is 3,93 g/cm3.
The surface of Mars (from the North Pole [top] to 60 south latitude) in the projectionMollweidego. Fig. HST / NASA.
Planet's surface temperature changes from about 170 to 300 Kelvins. Amount of solar energy incident per unit time per unit area of Mars is only 40% of energy reaching the earth's surface.
Mars has two moons with irregular shapes. They may be captured asteroids or celestial bodies formed from matter ejected by the impact of the planet's surface. They've been discovered by Asaph Hall in 1877. Their names come from the names of the sons of the greek war god Ares, Phobos (what means "fear") and Deimos ("anxiety"). Ares counterpart in roman mythology was Mars.
The geological history of Mars can be split into many epochs, but the following are the three primary epochs:
- Noachian epoch (named after Noachis Terra): Formation of the oldest extant surfaces of Mars, 4.5 billion years ago to 3.5 billion years ago. Noachian age surfaces are scarred by many large impact craters. The Tharsis bulge, a volcanic upland, is thought to have formed during this period, with extensive flooding by liquid water late in the epoch.
- Hesperian epoch (named after Hesperia Planum): 3.5 billion years ago to 2.9–3.3 billion years ago. The Hesperian epoch is marked by the formation of extensive lava plains.
- Amazonian epoch (named after Amazonis Planitia): 2.9–3.3 Gyr ago billion years ago to present. Amazonian regions have few meteorite impact craters, but are otherwise quite varied. Olympus Mons formed during this period, along with lava flows elsewhere on Mars.
Mars is the most similar planet to Earth and that's why it is suspected that on it's surface may live primitive forms of life. Two Viking spacecrafts that landed in 1976 on the Red Planet's surface, did not bring a solution to this problem. In 1996 it was announced that a meteorite found in Antarctica, ALH 8400, originating from Mars which contains traces of primitive life from before 3.6 billion years. Of cours it is not a proof that on Mars existed any life. It is only hypothesis encouraging for further research. One of the priorities of prepared and planned space missions to Mars is looking for traces of life on it.
