This paper will explain the internal composition between two classes of planets displaying differences in densities. Secondly,this paper will explain why their compositions are different.
The density difference between the giant planets and the inner planets derives from the planet’s internal composition. As in chapter 2 in the textbook, the origination of our planets derived from an original cloud formation, which orbited around the young sun and contained the following gas elements: hydrogen, helium, oxygen, nitrogen and neon. It also contained the following rock and metal elements such as iron, magnesium, silicon, and sulfur. After millions of years, these elements eventually formulated into huge rock-like material called planetesimals. The planetesimals that were closer to the Sun contained mainly rock and metals which are the prominent elements in the inner planets: Mercury, Venus, Earth, and Mars. The main reason for this inner planet composition was due to the dissipation of the light gases from the Sun's radiation. The further away the planetesimals were from the sun, the less gas dissipation occurred; thereby, leaving mostly ice and rock. Eventually, over time hydrogen and helium became the two main dominant elements found in the giant planets (Jovian planets): Jupiter, Saturn, Uranus and Neptune. For example, the composition of Jupiter is liquid hydrogen [light weight gas] and helium, 318 times the Earth’s mass. The Earth’s size core in Jupiter is composed of metal and rock which is 10 times the mass of Earth.In summary, these massive gas filled planets are very conducive to the density of water (water = 1) versus the inner planet’s density which is composed of rock/metal. The tremendous gravity is an essential force to hold the gas filled planet together. (Universe and Beyond, pg 21, 41-42, 2004)
In the regard to the density and composition of the four giant planets, the following can be noted. The main composition difference between the four Jovian planets is that Uranus and Neptune have methane, ammonia and water in the middle layer instead of the metallic hydrogen that Jupiter and Saturn both have. In both Jupiter and Saturn, the gas elements consist of 4/5 hydrogen and 1/5 helium. The density of Jupiter is 1.133 grams per CM3. Beginning from the top layer to the core, Jupiter is composition consists first withgastric hydrogen cloud covered top; next with the liquid hydrogen layer; then the metallic hydrogen layer; ending with an iron and silicate core. Temperature and atmospheric pressure in Jupiter starts out as a minus 120 degrees Celsius with an atmospheric pressure that is 70% of Earth’s surface pressure. The pressure and temperature increases with depth. By the time you get to the core, the temperature reaches 30,000 degrees Celsius or five times hotter than the sun’s surface; however, not hot enough to cause a thermo-nuclear fire which is why Jupiter can be called “the star that failed”. Jupiter’sdensity is1.33 g/cm3. Due to the planet’s significant rotation speed, atmospheric storms within the planet distribute the gases from high to low pressure. Saturn, the second largest planet has the same composition as Jupiter except it is cooler and less active. The density of Saturn is .71g /cm3. The thick atmosphere consists of 7/8th hydrogen, 1/8th helium. The rest of the planet is made up ofhydrogen compounds and has a rocky core. The density of Uranus is 1.24 g/cm3. Uranus consists of somewhat of a soupy atmosphere which is 7/8 hydrogen and 1/8th helium with the mixture of hydrogen compounds such as methane, ammonia, ethane, acetylene, and ethylene. The rocky core is covered with liquid methane, carbon monoxide and ammonia. The temperature starts out a minus 215 Celsius where it eventually increases with depth along with increased pressure. The whole planet has more of a liquid consistency to it. The density of Neptune is 1.67 g/cm3. Neptune composition is composed of Hydrogen compounds(methane, ammonia, and water) with smaller traces of hydrogen, helium, metal and rock. Uranus has compositions of Hydrogen compounds, rock, hydrogen, and helium. One interesting fact of Neptune is that the outer atmosphere rotates slower than the core and at different rates depending on latitude. This causes friction and produces heat for the planet.(Universe and Beyond, pp 46, 47-48, 50- 52, 52-53, 2004)
This paper explained the internal composition between two classes of planets displaying differences in densities. Secondly, this paper will explain why their compositions are different.