A Comparison of the Planets in the Sol System
December 19, 2004
Beginning Mercury, this paper will compare the nine planets and major moons of our solar system and describe their individual characteristics. At the end of this discussion, the habitability factor of these different worlds will be discussed as compared to that of the Earth's.
A Brief History of the Sol System
By radiocarbon dating meteorites, we know that roughly 4.6 billion years ago our solar system began. This happens when a cloud of gas and dust were disturbed and squeezed by perturbations of the surrounding space, possibly caused by an exploding supernova. As the cloud began to contract and spin around a common center of gravity, it also began to heat. After about 10 million years of condensing and heating, our solar system began to take shape. Towards the center of the cloud, it was hot with cooler areas at the edge. It is possible that this heating and cooling was even within the cloud. A line called the frost line began to grow. Inside the frost line, planetesimals made of rocks and metals began meshing and colliding, becoming the terrestrial planets. Outside of the frost line, nebulae were accreting around ices and would become the Jovian planets. The cloud further contracted towards its center and eventually became hot enough to begin nuclear fusion. This is the birth of our star, the Sun, and of our solar system. Stellar winds from the ignition blew excess materials into the fringes of our newly formed solar system as well as the interstellar medium.
The Nine Planets
During the accretion phase of the birth of our solar system, hundreds to thousands of planetesimals congregated and coalesced. However, eight true planets have survived to this day with the ninth possibly being the largest of the Kuiper Belt objects. These planets are broken into two sections, inner solar system and outer.
The Inner Solar System Planets and Moons
Mercury (The Messenger of the [Greek] gods)
Mercury is the smallest of the inner solar system planets is also the closest to the sun. At .39 AU (1 AU = 93,000,000 miles), it orbits the sun every 87.9 days, faster than any other planet in the solar system. Mercury is composed of rocks and metal (iron mostly) and has a day temperature of 797o F and a nighttime temperature of -240o F. There is no atmosphere, no volcanism, no signs of life and a heavily cratered surface. Mercury is about a 5th the size of Earth. Some curious features of Mercury are the cracks around its surface. Some of these cracks have created cliffs that are thought to be the product of planetary shrinkage, which may have happened early in Mercury's history when the core cooled and rather rapidly. Mercury has no moon.
Venus (The goddess of Love)
Venus is the second largest planet within the inner solar system and second from the sun at .72 AU with an orbital period of 225 days it is second fastest around the sun. Venus is composed of rock and metal with an average temperature of 850o F. This is due to the greenhouse effect produced by an over abundance of carbon dioxide in its atmosphere. The atmosphere on Venus has no oxygen and the pressure of its atmosphere is nine times that of Earth's at ground level. There is evidence of volcanism in the past and the relative present. Also, Venus has no water and no signs of life. A curious feature of Venus is its squat volcanoes. This is possibly due to the massive pressure of Venus' atmosphere on the ground. It is thought that when lava erupts from within the planet, the pressure keeps the lava from spewing upwards. Instead, it oozes out like tooth paste being slowly ejected from its tube. Venus is just slightly smaller than Earth and has no moon.
Earth (ground, soil, dry land)
Earth is the largest planet in the inner solar system at a distance of 1 AU from the sun with an orbit of one year and is...
References: The Cosmic Perspective, Third Edition
Bennett, et al, 2004
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