The Planets of Our Solar System
Our solar system consists of 8-planets that circle around the sun. The word for that circling is called an orbit or orbits. The planets circle counter-clockwise in their orbit around the sun with Mercury being the closest planet to the sun, followed by Venus, Earth, and Mars. This is considered the inner solar system, the planets that orbit closest to the sun and are made up of rocks.
Around the inner system is an asteroid belt, which is an area that circles around the inner system and is where thousands of asteroids orbit. The outer solar system consists of Jupiter, Saturn, Uranus and finally Neptune. This set of planets are much further from the sun and orbit farther from each other than those in the inner system.
For the past eighty or so years, our solar system contained 9-planets, but in 2006 the International Astronomical Union (IAU), after much debate, redefined the definition of a planet. They decided that to be classified a full-fledged planet it would have to be:
1 - In orbit around the sun.
2 – Had enough mass that its self-gravity would cause it to be spherical (nearly round).
3 – Had to have cleared the debris from its orbital path.
While Pluto’s orbit and mass passed their definition, it did not pass the third. Pluto travels through the Kuiper Belt, which is full of space debris. These new standards changed our solar system from 9 to 8 planets. A new classification was created called dwarf planet. A dwarf planet would than fit the first two categories, but not the third. While Ceres and Eris have also been classified as dwarf planets, there are close to fifty more that are being considered for the same classification.
All of the planets in the solar system orbit around the sun. The sun turns on its axis just like all the planets do. A globe is a good example of how a planet turns, although the planets don’t all turn at the exact same angle. The sun is a medium-sized star called a dwarf star. It is made of hydrogen and helium, which are gases and make it a burning fireball. The sun is like a furnace that it is a hundred times hotter than the hottest day here on Earth. The sun is so large that you could fit more than a million Earths inside of it. Without the sun the Earth would die, it supplies us with heat that warms us and light that sustains all life.
Mercury is the planet closest to the sun, although it is about 36-million miles away from it. Mercury is only around two-fifths the size of Earth and because it is small and so close to the sun it is sometimes difficult to see with the naked eye. You have to know when and where to look, at certain times of the year it is low in the sky off to the west and at others it can be seen in the east.
Mercury’s surface resembles the moon and its orbit is oval-shaped and moves around the sun faster than any other planet, about every 88 days. The ancient Romans named Mercury after a very fast messenger they believed in, who was a servant to their gods. With no real atmospheric protection, it is very dry with almost no air and because of distance to the sun very hot, with temperatures over six times as hot as those on Earth.
Venus is the second planet from the sun. Its surface is like the moon, but it also has inactive volcanoes. It can be seen at sunset and sunrise because it is very bright, so it is often called the “Evening Star” and the “Morning Star.” While it looks like a star, it is not. Stars twinkle and Venus does not.
Time goes by slowly on Venus because it turns so slowly; a day lasts 243 Earth days! A year on Venus is 225 days. That means that a day there lasts longer than a year there. Like Earth in some ways, Venus is about the same size and it also has about the same gravity, but unlike Earth and other planets, Venus turns backwards and the atmosphere is made up of almost all carbon dioxide. Venus has no oceans and the planet is covered with clouds of sulpheric acid that allow sunlight in, but trap the heat in, this causes the temperature on Venus to be around 900º.
Earth is our planet, our home and is the largest of the inner planets. It is made up of about 70% water and is the only planet that has water on its surface. Around the water are islands and large land areas called continents, which have various landforms consisting of mountains, active and inactive volcanoes (no other planets have active volcanoes), deserts, plains, forests and marshes. Because of this eco-system, plants grow and animals can live. This is not seen on any other planet known to man.
The Earth turns in a 24-hour cycle, which is much faster than other planets and its orbital year is 365-days long. The atmosphere is mainly oxygen, which allows animals and people to breathe, while the rest is made up of nitrogen, carbon dioxide, argon and other gases. It is also holds about 1% in water vapor. The atmosphere is also protected in such a way as to only allow a certain amount of the sun’s rays to penetrate, which gives us temperatures that usually do not exceed 100º F in summer or under an average of around -60 F in the colder regions. The earth also has only one moon.
Mars is the fourth planet from the sun and because of its color is nicknamed the “Red Planet.” The planet is sandy with a bulky rock surface and hills. Much like Earth, Mars spins quickly with a 24 hour and 36 minute rotation or day, but a year there lasts 687 of our days. Its atmosphere is made up of mostly carbon dioxide, then nitrogen and oxygen, although the oxygen levels are too low for a person to breathe. Mars also has water vapor, but it has four times less than on Earth. Because of that, it may be possible that it rains on Mars, but no one can be sure. Scientists have seen the terrific dust storms on Mars, so they know that there is wind.
Jupiter is the fifth planet from the sun. It is a big red striped ball, the largest planet in our solar system. The ancient Romans named Jupiter after one of their gods, whom they called the “King of gods” and was so named because of its size. It is mostly made up of hydrogen with smelly clouds of ammonia and Sulphur and clouds of water vapor.
The planet Jupiter has 4 rings around it called Halo, the main ring and two Gossamer rings. It also has 16-moons or more, some of which are located within its rings Jupiter has a stormy atmosphere with winds of over 250 miles per hour and there are often photos taken of them by scientists, as there is a very large one they know of that has lasted for hundreds of years.
Saturn is the sixth planet from the sun and also the second planet in the outer solar system, as well as the second largest planet. It is so big that it can be visually viewed in the night sky. Ancient Romans and Greeks named it Saturn. In 1655, it was discovered that Saturn had rings when Christian Huygens made a better quality telescope.
Hydrogen and helium are liquids on Saturn and are what the planet is made up of. Here on Earth these elements are gases. Like Earth, Saturn has weather, consisting mostly of windstorms, which when photographed appear as bright blue and yellow areas on the planet. Saturn’s usual color is yellow due to there being so much Sulphur in is its atmosphere.
Saturn has so many moons (18) that it is said to have its own system. It is also known for its visible rings, which are made up of very small to massive sized rocks and ice. Because the sun reflects on the rings, they are very colorful like a rainbow, as the light reflects off of the ice and dust particles. Saturn rotates quickly and has a 10-hour day, but its year is 29 ½ of our years long!
Uranus is the seventh planet from the sun and has the most moons of any planet in the solar system, with 18 that have been confirmed and probably more to come. A day only lasts 17-hours, but its year is 84 of our years long! That’s how long it takes to orbit the sun once. It was first discovered by William Herschel in 1781 and was named after another Roman/Greek god like the other planets.
Uranus is very cold and is made up of methane, which would be a gas here, but because of the cold is an ice there. The atmosphere is made up of clouds of methane gas that cover the entire planet, giving it a blue to green color. It is very windy, with gusts up over 300 miles per hour. Its north and south poles are in the middle, so compared to Earth it would be sideways with the poles located in the middle.
Neptune is the eighth and last planet in our solar system. Neptune is desperately cold and is another blue planet made up of methane gas with a similar day to that of Uranus in that it is about 17-hours long, but a year lasts 165 of our Earth years because of its far distance from the sun. Neptune has a very large blotch on its surface, which scientists believe to be a hole in its methane gas atmosphere. The surface, like Earth, is ever changing in appearance due to the narrow bands of white clouds that move about. There are also 8 moons circling Neptune, one so large that it was named, it is called Triton.
We know quite a bit about the planets closest to us, but little is known about those at the far ends of our solar system. While we understand their basic structure and what they look like, there is not a lot of other information we can have about them. That is if and until we can make our way into those outer limits of space and visit them up close.
The Solar System
Nine Planets A multimedia tour of the solar system for kids.
N.A.S.A. Moons and planets of our solar system. Includes: Plutoids and beyond our solar system.
Kids Astronomy A click and learn solar system.
Sites for Teachers Click on a planet and you are linked to an informational page on each.
National Geographic An article about the discovery of 32 new planets.
The planets and our solar system.
Space All about meteors.
American Meteor Society Site with photos, videos, graphs, teaching tools and links.
Star Date Constellation guide, calendar to meteor events and much more!
Windows to the Universe All about meteors.
International Meteor Org. Observation methods links.
Solar Views An introduction to asteroids.
Smithsonian National Air and Space Museum. Exploring the planets asteroid pages.
Science Now An article titled: Earth Can Shake Up Asteroids, Too
The Planetary Society Space Topics: Asteroids and Comets.
Lunar Outpost Explanation with a fun scale to see what you would weigh on an asteroid.
Kidepede All about Comets.
Berkeley College History/exploration, origins, make a comet; play a game, orbits and more!
Why Files We have leftovers, but so do comets. Read what they leave behind.
Creative Kids Make your own comet at home.
Our Universe Labs, fun and news
Cool Cosmos Ask an astronomer page – Linked pages with questions and answers.
Kids Web Japan An origami experiment from a spacecraft.
The Phoenix to Mars mission and the Mars Lander.
Knowledge House Spacecraft 101 – The Spirit land rover story.
Hubble All about the Hubble spacecraft, with pictures and image tours.