Planetary Comparison

SCI/151

May 3, 2011

Norman Stradleigh

Planetary Comparison

Planet Earth is the third planet from the Sun and the fifth largest of the planets of the Solar System. Earth’s surface is 71 percent water and is the only astronomical planet currently known where life exists. Earth is our home planet. Scientist and astronomers have studied our planet for Centuries and they have discovered much about our planet. Scientist have gained so much more knowledge of our Solar System in the last half-century after the NASA launched the first spacecraft and travel beyond Earth’s atmosphere has opened up to those who wish to explore. In the following paragraphs, we will discuss Earth and the comparison between the other known planets in our Solar system.

Earth has several layers that have distinct chemical and seismic properties: Crust, Upper mantle, Transition region, Lower mantle, D’’ layer, Outer core, and Inner core. The crust, the part we inhabit, is just a tiny fraction of the Earths mass. Most of the mass of the Earth is in the mantle, a majority of the rest is in the core (Nine Planets, 1994-2010). Earth has three layers of density: The core primarily metals, such as nickel and iron, resides in the central core and is the highest-density material. The Mantel forms the thick mantle that surrounds the core is mostly minerals that contain silicone, oxygen, and other elements and is a rocky material of modest density. The Crust essentially represents the worlds’ outer skin and consists of the lowest density rock, such as granite and a common form of volcanic rock called basalt. Seismic studies indicate Earth has a solid inner core and a molten outer core.

Seismic waves, vibrations created by earthquakes, have provided geologist with much of the information we have about the Earth’s interior. Seismic waves come in two basic types that are analogous to two waves we can generate waves. P waves, pressure or pulling, can travel through almost any material because the molecules can always push on their neighbors, even when weakly bound together. S waves, meaning shear or side-to-side, travel only through solids, because the molecules in liquid and gas are too weak to travel up and down. Geologist know that Earth has a liquid layer in its outer core because the P waves travel faster and are the first to arrive after an Earthquake, reaching the side of the world opposite the earthquake and the S waves do not because the liquid layer has stopped the S waves (Bennett, Donahue, Schneider, Voit, 2009). The Earth’s surface is solid, but regardless of how solid the surface, there are many elements that erode the surface and reshape it over time. The flow of the rivers through the land and mountains over many years of rapid flow widens the surface, carves out grooves, and valleys. Tens of millions of years of wind, rain, and ice has cut down the size of the mountain peaks. Continents move slowly about, completely rearranging Earth’s surface every few million years, according to Bennett, Donahue, Schneider, and Voit (2009). Mercury is the smallest of the first eight planets in our Solar system, with no volcanoes, no wind, no rain, and no life. Mercury’s proximity to the Sun makes it difficult to observe. From what scientists were able, to learn from Mariners 10’s rapid flybys in 1974 – 1975, Mercury is a very hot and extremely cold planet. Mercury appears to be made mostly of iron with craters, lava flow, and tall, steep cliffs (NASA, n.d.). Its interior appears to resemble Earths. Both planets have a rocky layer called a mantle beneath their crust and both planets have an iron core. However, Mercury has no moon, compared to Earth’s one moon. According to NASA (n.d.), Venus is similar in structure and size to Earth, which is why Venus is called Earth’s sister planet, except it has no moon. Its atmosphere traps heat in a runaway “Greenhouse effect” (Venus, para. 1). Venus is unique in the fact that it spins slowly in the opposite direction of the other planets. It is a cloudy, dim world of intense heat, volcanic activity, and deformed mountains on the surface. Mars is a rocky body about half the size of Earth. Like Earth, Mars experiences seasons because of the tilt of its rotational axis, so its distance to the sun changes, according to NASA (n.d.). Telescope observations show water-iced clouds, polar ice, and volcanoes. Mars has the largest Volcanic Mountain in the solar system, named the Olympus Mons and has two moons in its orbit. Jupiter is the largest and the fastest spinning planet in our solar system. The storm on Jupiter known as the Great Red Spot could swallow up the entire Earth. Jupiter is made primarily of hydrogen and helium and has no solid surface. Its atmosphere resembles that of the sun. Stathopoulus (2000 – 2011), “ Sixteen moons have been identified, with Ganymede noted as the largest - it is bigger than both Mercury and Pluto” (Facts about Jupiter, para. 9). Saturn is unique of all the planets, adorned with thousands of beautiful ringlets and has 63 moons with confirmed orbits. Fifty-three of the moons have been named, with Titan being the largest and the only one with an atmosphere. Saturn is mostly a massive ball of hydrogen and helium, much like the planet Jupiter. Uranus is the only giant planet whose equator is nearly at right angles to its orbit and has 5 large moons and 22 smaller moons. It is, also, the only planet in our solar system to spin on its side. Uranus is mainly hydrogen and helium, but has a lot of methane in its atmosphere than Jupiter and Saturn, which gives it a blue tint. Neptune, known as the Blue planet, is the last of the gas planets in our solar system. Its atmosphere is mostly comprised of hydrogen, helium, and methane. Like Earth’s atmosphere, it has clouds and storm systems that revolve around the planet, but with high wind speeds and frozen methane clouds (NASA, n.d.). Neptune has 13 moons, which can be divided into two groups, regular and irregular. The irregular moons are smaller than the regular moons of Neptune. This concludes our discussion of the eight planets in our solar system, however, Pluto should not go without mention. Pluto was thought to have been a planet in our solar system for centuries. There have been some discussions in the last decade debating if Pluto was a planet or a comet. Since our course still has Pluto listed as one of the nine planets in our solar system, we will discuss the attributes of it as a planet. Pluto is the smallest planet in our solar system. Its surface composition is nitrogen, carbon monoxide, methane, and water ices. It is the farthest known planet from the sun and is the only planet not visited by spacecraft (Stathopoulus, 2000 – 2011). Our review of the planets revealed the four inner planets are much different from the four outer planets. The four terrestrial planets: Mercury, Venus, Earth, and Mars have rocky surfaces and metal deep in their interiors. They are small and dense with few moons and no rings. While the Jovian planets; Jupiter, Saturn, Uranus, Neptune have numerous moons and rings. They are larger and lower in density being comprised of mostly gases. All of the planets in our solar system must have looked much different when they were younger. Just as the Earth’s surface has altered over the centuries, the surface of the other planets in our Solar System must have changed over time as well, from the different elements on their planet.
References
Bennett, Donahue, Schneider, Voit, (2009). The Cosmic Perspective (5th ed.). San Francisco, CA: Addison-Wesley

NASA. (n.d.). Solar System Exploration. Retrieved from http://solarsystem.nasa.gov/planets/
Nine Planets. (1994-2010). Earth. Retrieved from http://www.nineplanets.org/earth.html

Stathopoulus, Vic. (2000 - 2011). The Planet Jupiter. Aerospace Guide. Retrieved from http://www.aerospaceguide.net/planets/jupiter