The Terrestrial Planets

A planet is a celestial body that revolves around a central star and does not shine by its own light. The only planetary system that is known to man is our solar system. It is made up of nine planets, which range in size and make-up. The terrestrial planets in our solar system are Mercury, Venus, Earth, and Mars. There are also many other minor planets, which are also in our solar system, but they are unimportant compared to the major planets. In this paper, I will discuss the terrestrial planets and how they are each unique.

Mercury, which is the planet that is closest to the sun, is the first planet I will discuss. Mercury is the smallest of the inner planets. It is speculated that the heat from the sun made it impossible for the gases present to become part of the planetary formation. The surface of Mercury is extremely hot. It is approximately 470 degrees Celsius on the surface and is thought to be even hotter at the two "hot spots". These "hot spots" are on opposite ends of the equator. It is the heat of the surface that makes it impossible for Mercury to have any type of atmosphere. Mercury orbits the sun once every 88 days and has a true rotation period of 58.6 days. It is the closest planet to the sun and therefore orbits faster than any other planet. It is said that Mercury rotates three times for every two trips around the sun, so that during every alternate perihelion passage the same face points directly at the sun. Geologically, the most remarkable features of Mercury are compress ional cliffs or faults, just the sort of wrinkles that might form in the crust if the interior of the planet shrank slightly. It is speculated that it was the solidification of Mercury\'s metallic core that caused this global shrinkage. Mercury is also enriched
in metal or depleted of rock. It is also believed that some of the inner core of Mercury is still in a fluid state. Scientists also believe that Mercury\'s surface is made partially of silicate rock. The best way to describe Mercury is: small, heavily cratered, and airless.

Venus is the second closest planet to the sun and is said to be most closely resemble Earth in size and density. Venus is known to most scientists as the sister planet to the Earth. It
is called this because it closely resembles the Earth\'s mass, density, and diameter. The only thing different is that Venus is shrouded in thick clouds that completely hide the surface of the planet. The surface temperature is also much warmer than that of Earth. Venus completes one revolution around the sun in 224.7 days. This makes the Venusians day equal to 117 earth days. It is thought that this slow rotation may be the reason why Venus has no magnetic field. The atmosphere of Venus made up of 98% carbon dioxide and 2% Nitrogen. This atmosphere also has the presence of helium, neon, and argon. This is yet another thing which makes Venus
different from Earth. The surface of Venus is quite a bit like that of the Earth. The surface has volcanoes and smooth plains. Much of the volcanic activity on Venus takes the form of Basaltic eruptions that inundate large areas, much as the mare volcanism flooded the impacted basins on the near side of the moon. One thing that differs from Earth is that there is no water liquid on the Venusian surface. Venus, although different from Earth, is still our sister planet.

Earth is the largest of the terrestrial planets and the only planet to support life as we know it. It\'s surface is a wrinkled layer of solid rock called the crust, which is between 10 and 32 km thick; the oceans, comprising about 2/3 of the Earth\'s surface, fill the crust\'s deepest basins. The areas not covered by water are the seven continents of Africa, North and South America, Asia, Australia, Europe, and Antarctica. Our atmosphere, composed of 78% nitrogen and 21% oxygen, is the only one in the solar system which provides the oxygen that humans need to breathe. Earth’s day is 23.hours and 56 minutes, its year 365.25 days. The