Terrestrial and Jovian Planets

Terrestrial and Jovian Planets

Our solar system contains nine planets, which are broken down into 2 classifications known as terrestrial planets and jovian planets. The terrestrial planets are composed primarily of rock and metal. They also generally have high densities, slow rotation, solid surfaces, no rings, and few satellites. These planets include Mercury, Venus, Earth, and Mars. On the other hand, the jovian planets are composed primarily of hydrogen and helium. They generally have low densities, rapid rotation, deep atmospheres, rings, and numerous satellites. These planets include Jupiter, Saturn, Uranus, and Neptune.

The closest terrestrial planet to the sun is Mercury. Mercury is relatively small, and technically the eighth largest of all the planets. It is actually smaller in diameter than the moons Ganymede and Titan. Mercury has been visited by only one spacecraft, and that was the Mariner 10. The temperature variations on Mercury are the most extreme of any in the solar system. Temperatures range from 90K to 700K. Venus is slightly hotter, but much more stable. Mercury is in many ways similar to the moon. The biggest comparison is the surface being heavily cratered and very old. Mercury is also the second densest planet in the solar system, only behind earth. Mercury actually has a very thin atmosphere consisting of atoms blown off the planet by solar winds. Mercury is often visible with binoculars, and sometimes even the naked eye. The best place to find Mercury is always near the Sun.

The next terrestrial planet, and second planet from the sun, is Venus. Venus is the brightest object in the sky except for the Sun and the Moon. The first spacecraft to visit the planet was the Mariner 2 in 1962. It has also been visited by many other spacecrafts, including the Pioneer Venus, Venera 7, Venera 9, and most recently the US spacecraft Magellan. The rotation on Venus is somewhat unusual because it is very slow and also retrograde. One day on Venus is equivalent to 243 days on Earth. The atmosphere on Venus is composed almost entirely of Carbon Dioxide. It contains several layers of clouds made up of sulfuric acid. These clouds completely cover up our view of the planet. The dense atmosphere produces a greenhouse effect that raises the temperatures to nearly 400 degrees, which is 740K. Venus' surface is actually hotter than Mercury's, despite being nearly twice as far from the Sun. There are also very strong winds on the planet that reach up to 350 kph. Venus is usually visible to the naked eye. Being the brightest star in the sky makes Venus easily seen on starry nights.

The next terrestrial planet, and third planet from the Sun, is our Earth. Earth is the only planet whose English name does not derive from Greek or Roman mythology. Earth is the densest major body in the solar system. Unlike the other terrestrial planets, Earth is divided into solid plates that float around independently on top of the hot mantle. There are eight major plates and twenty or so smaller plates. Seventy-one percent of the Earth is made of water. Earth happens to be the only planet on which water can exist as a liquid form on the surface. The Earth's atmosphere is 77% nitrogen, 21% oxygen, and has traces of argon, carbon dioxide, and water. Earth is the only planet with human life, and as a result, this is planet is our home.

The last terrestrial planet, and fourth planet from the Sun, is Mars. Mars is a fairly small planet, and as a result is the seventh largest of all the planets. Mars is commonly referred to as the Red Planet, due to its red color. The first spacecraft to visit Mars was the Mariner 4 in 1965. Several others closely followed including the Mariner 2, Viking, and Mars Pathfinder. Mars has a very thin atmosphere composed of 95.3% carbon dioxide, 2.7% nitrogen, and 1.6% argon. Mars thin atmosphere also produces a greenhouse effect, however it only raises the temperature slightly. When it is nighttime, Mars is easily visible to the unaided eye.

The fifth planet from the Sun, and first of the jovian planets, is Jupiter. Jupiter is by far the largest of all the planets. Jupiter is more than twice as big as all the other planets combined. Jupiter happens to be the fourth brightest planet in the sky, only behind the Sun, Moon, and Venus. Jupiter was first visited by the Pioneer 10 in 1973. Jupiter is the first of the gaseous, and therefore does not have a solid surface. However, the gaseous material gets more and more dense with depth. Jupiter is made up of 90% hydrogen, and 10% helium. Jupiter is also home of the Great Red Spot. The Great Red Spot is a high pressure region whose clouds are higher and colder than the surrounding regions.