Earth and Our Solar System

Earth is the only planet in our solar system that sustains life, and therefore one of the most intriguing planets because of its capabilities. Each of the seven other planets that orbit the same sun as Earth is interesting in its own way. Some planets share similar characteristics to those found on Earth, while other planets are completely different. An analysis of these terrestrial bodies, using comparative planetology, will allow us examine these qualities. However, before beginning such a process we must first gain a through understanding of the makeup of our own planet, Earth. We begin by identifying two types of families of planets, rocky terrestrials and gaseous jovians. The latter planet made of gas with no solid surface. The atmospheres of these gaseous giants show a thicker density as you move closer to the core. However, unlike Earth’s rocky surface a gaseous jovian cannot be stood on. The four gaseous jovians in our solar system are Jupiter, Saturn, Neptune, and Uranus. Rocky terrestrials are the types of planets that possess a solid surface made of rock. Mars, Venus, and Mercury are examples of rocky terrestrials in our solar system. Of course, Earth is one of them as well. Earth’s interior is comprised of three main layers, according to levels of density. The core consists of metals such as nickel alloy and iron and is known to be highly dense. The layer surrounding the core is called the mantle. This layer is less dense than the core and is very thick. The Earth’s mantle is made up of different minerals and has high ranges in temperatures. The third layer is the crust, a portion of mass that is very thin when compared to the other two layers. The crust is made up of basalt and granite, considered to be the lowest density rocks within all of the planet’s layers.
Scientists have the capabilities to determine the internal structure of our planet by using readings of seismic waves created by earthquakes. There are two different types of waves that travel through the Earth’s interior. They are primary waves (P waves) or secondary waves (S waves). Scientists study the speed at which they travel at and finally arrive at the other end of the planet. This process helps scientists determine what kind of materials the waves pass through along Earth’s interior. The factors, such as density, temperature, and pressure, of the different layers of our planet affect the speed at which these waves travel. It is these observations that allow researchers to gain a clear picture of what the inside of Earth is made up of.
Rocky terrestrials, such as Earth, Mars, and Venus, also share similar geological processes that create their shapes. An example of one of these processes is volcanism, which “refers to any eruption of molten lava onto the surface, whether it comes from a tall volcano or simply rises through a crack in a planet’s lithosphere (Bennett, p 258). As the lava erupts it eventually solidifies and creates new ground. Lava can be of a liquid form and run a great distance before solidifying, creating volcanic plains. It can also take on a thicker form that doesn’t travel as far but builds up around the opening that caused it to spill. This build up of new ground creates shield volcanoes and strato-volcanoes. A second geological process that affects rocky terrestrials is impact cratering. These craters “form when an asteroid or comet slams into a world with a solid surface” (Bennett, p257). The incredible speed of the object making impact releases enough energy to shoot debris out from under the surface and crate a giant crater. This collision leaves a hole in the planet’s surface that is sometimes 10 times bigger than the object that caused the impact.
“Erosion is a blanket term for a variety of processes that break down or transport rock through the action of ice, liquid, or gas” (Bennett, p 260). Water is a powerful force here on Earth but not really found on other planets. Erosion on Mars, Venus or Mercury is mainly caused by wind or ice, elements that are also found on Earth. As these elements make their way through or around sand, dirt, or rock they create dunes, riverbanks, and valleys. The lithosphere under the crust of a rocky terrestrial is broken up into large plates we call plate tectonics. This break up was caused by mantle convection, where rocks in that layer push against each other. This causes the plate tectonics to move around each other, or sometimes over and under other plates. “The movement of the plates explain nearly all Earth’s major geological features, including the arrangements of the continents, the nature of the seafloor, and the origin of earthquakes” (Bennett, p 260). We have now seen the similarities between the interior structures of the rocky terrestrials, Earth, Mercury, Venus, and Mars. However, these planets also have their own unique qualities. For example, Mercury has a very thin atmosphere that does not allow for air, rain, or ice to affect the geology of its surface, nor does it have any active volcanoes. Therefore, unlike Earth, the only process that affects the surface of Mercury is impact cratering. Venus’ unique quality is that it has an atmosphere that has ninety times the pressure found in Earth’s atmosphere. This is an environment where oxygen cannot exist because of the high temperatures and pressure, which do not allow liquids to fall from the clouds.
Mars is the planet in our solar system that is most like our own planet. Not only is the interior structure similar to Earth but the planet also has active volcanoes, canyons, and frozen water and carbon dioxide on its north pole. The planet has a thin atmosphere that is slowly being blown away by the Sun’s solar winds. A unique quality about Mars is that its atmosphere is missing an ozone layer. This means that ultraviolet radiation from the Sun penetrates the planet’s atmosphere easily. The jovian planets are obviously very different from Earth being that they do not have any solid ground to stand on. However, they each have their own unique characteristics. For example, Jupiter, like other jovians, has high velocity winds that create bands that flow in opposite directions. Jupiter is unique in that its slight chemical and temperature differences create color among these bands, making them clearly visible from Earth. Saturn is very unique in that the shape is somewhat flattened, more than the other jovian planets. The diameter across the equator and that of the polar caps varies by less than 10%. This is due to the very fast rotation of Saturn and its very liquid state. The last two planets in or solar system are Uranus and Neptune, both also gaseous jovians. Uranus is a very unique planet because it is tilted on its axis, along with its rings and moon, to the point where its poles directly face the Sun. “This unusual orientation may be the result of a cataclysmic collision that Uranus suffered as it was forming some 4.6 billion years ago,” (Bennett, p 211). Neptune possesses a spot similar to that or Jupiter’s red spot, although it is half the size and dark in color. What is unique about this spot is that it moves in the opposite direction as Neptune’s rotation. Neptune’s great dark spot is also unstable. It disappeared shortly after its discovery and reappeared on the northern hemisphere in 1995. There is little doubt of the magnitude offered by the mysteries of our solar system. Scientists have proven to know so much about it and yet know so little. The one thing we do know is that for now, Earth is the only planet we can call home. The characteristics of this warm planet are perfect to sustain life without the extensive reliability of advanced technology. However, this may not always be the case. We are just beginning to learn about the other seven terrestrial bodies in our galaxy and maybe one day we might call one of them home.

References:
Bennett, J., Donahue, M., Schneider, N. & Voit, M. (2007). The Cosmic Perspective (4th edition). Pearson/Addison Wesley. San Francisco, CA.

References: Bennett, J., Donahue, M., Schneider, N. & Voit, M. (2007). The Cosmic Perspective (4th edition). Pearson/Addison Wesley. San Francisco, CA.