As the four planets on the inner part of the solar system, Mercury, Venus, Earth and Mars are similar in that they are rocky in nature and have compact solid bodies. However, their differences are quite vast when it comes to their temperatures, atmospheres and landscapes.
Planet Mercury
Mercury is named after a Roman mythology god and is the second smallest planet of the solar system. The planet is the closest to the Sun with temperatures so extreme they range from -298° F to 800° F. These temperature variations are due to Mercury's very thin atmosphere, which is constantly being blasted off by the solar wind.
The planet has a very eccentric orbit talking it from 29 million miles at perihelion to 43.5 million miles at aphelion from the Sun. Its orbit around the Sun takes only about 88 days, but the daily rotation is very slow, taking Mercury 176 Earth days to complete its day.
Mercury's surface is full of craters and resembles Earth's Moon. It is possible that there was some recent volcanic activity as suggested by the appearance of some smooth plains. The planet's mantle and crust are composed of silicate, but inside there is a large iron core, of which half is most likely molten.
Planet Venus
This planet was named after the famous goddess of love and beauty, Venus, probably because of its brightness in the night sky. Venus is the sixth largest planet in the Solar System and has an almost circular orbit around the Sun. Its rotation is very slow and retrograde; it is also synchronized in such a way that it shows the same side to Earth when both planets are at their closest approach. A day in Venus is equal to 243 Earth days.
Venus is just a bit smaller than Earth with a similar chemical composition and density. However, the planet's surface is very hostile to humans, composed mostly of carbon dioxide. Many layers of sulfuric acid clouds hide the surface of the planet, which consists of rolling plains with some wide depressions. It probably had water like Earth at one point, but it all boiled away because of the planet's proximity to the Sun.
The temperature on Venus is actually hotter than on Mercury because of its greenhouse effect. Surface temperatures reach 740° K, which is hot enough to melt lead. Winds on Venus can get up to 218 miles per hour at the top clouds, but they are much weaker on the surface.
Planet Earth
Earth is the third planet from the Sun and the only one whose name is not derived from Roman or Greek mythology. The name Earth comes from Old English and Germanic. Earth is the only planet in the Solar System known to have intelligent life as, among other factors, it resides in the 'Goldilocks' region of the system. To be habitable, a planet should orbit far enough from the Sun so that its water doesn’t boil off and close enough to have mild temperatures for life to develop.
Earth is about 8,000 miles in diameter and is the fifth largest planet in the Solar System. It resides 93 million miles from the Sun and takes 365 days to orbit the star. Planet Earth is about 4.6 billion years old and is 71% covered with water. The atmosphere on the planet is stable and consists of 77% nitrogen, 21% oxygen with the rest being traces of argon, carbon dioxide and water.
Planet Earth has a Moon that orbits from almost 239,000 miles away and has a wide influence on the planet by means of tidal effects.
Planet Mars
Mars is named after the god of war, probably because of its red color. It is the fourth planet from the Sun and is just about over half the diameter of Earth. Mars is one of the most highly investigated planets of the Solar System. There have been multiple spacecrafts sent to study it and many are on its surface at the present moment.
Mars has always been the planet most likely believed to hold any kind of life. It is thought that it once had vast amounts of water and probably even a thicker atmosphere, much like Earth's. But evidence shows that the atmosphere was, and still is, stripped away by the solar wind. It does, however, have large amounts of ice water at its poles and soil samples have revealed compounds suitable for organic life to evolve.
The atmosphere of Mars is very thin, made mostly of carbon dioxide and small percentages of nitrogen and argon, there are traces of oxygen and water also. Temperatures range widely from -207° F to almost 80° F. A day in Mars is only a little longer than an Earth day, but its year is about double that of Earth because of its distance to the Sun.
These are just some facts about the four innermost planets in the Solar System. Large amounts of information exist about each distinct world. But, as astronomers advance in their research and knowledge, more will be known about these planets; maybe even evidence of life outside Earth will ultimately be discovered and studied.
Sources:
Nine Planets - Bill Arnett, Nine Planets Org.
Solstation - Sol Company
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