The solar system is the collection of eight planets and their moons in orbit around the Sun, together with smaller bodies in the form of asteroids, meteoroids, and comets. The gravitational attraction between the Sun and these objects keeps them revolving around the Sun.
The eight planets in their order of distance from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was once considered a full planet but was redefined as a dwarf planet in 2006.
The Sun is the center of our solar system. It is the largest body in our solar system. The eight planets follow paths called orbits around the Sun. The shape of each orbit is called an ellipse.
Moons, asteroids, comets, and meteoroids are also part of our solar system. Moons orbit planets. Asteroids, comets, and meteoroids orbit the sun. The sun is the only object in our solar system to shine with its own light. All other objects in our solar system reflect the light of the sun.
Giant dust storms, freezing temperatures, colorful clouds, and beautiful rings can be found throughout the solar system.
The Solar System is part of a bigger grouping of stars called a galaxy. Our galaxy is the Milky Way. The Solar System orbits around the center of the Milky Way.
The Sun is a ball of hot, glowing gases. It is much hotter than the eight planets. The outermost layer of the Sun that we can see is about 10,000°F. The hottest the oven in your kitchen gets is about 500°F. The Sun is the most important part of our solar system. It gives us warmth and light. Without the sun, our Earth would be very cold. If there be no Sun, there would be no life on Earth.
The Sun is the nearest star amongst all the stars present in the universe. It is the main source of heat and light for all the planets, especially Earth.
The Sun is a star. It is the closest star to Earth. At night we can see many stars in the dark sky. During the day, when we can see the sun shining, its light is so bright that we cannot see other stars. Some stars are hotter than our sun, others are cooler. Some stars are bigger than our sun and other stars are smaller, but they are so far away from Earth that they look like tiny points of life. Our sun is 10 times larger than the largest planet Jupiter.
Mercury is the closest planet to the sun. Because it is so close to the sun, Mercury gets very hot. During the day, the temperature on Mercury can get as high as 800°F (430°C). The hottest it has ever gotten on Earth is about 135°F (60°C). At night, when it is cold Mercury can also get very cold, as cold as -230°F (-175°C). This happens because there are no clouds and very little air surrounding the planet. The atmosphere helps to keep a planet warm when the sun is not shining. Mercury’s very thin atmosphere cannot keep the planet warm at night.
The surface of Mercury is hard and rocky. Mercury has cliffs and valleys just as Earth does. The surface of Mercury is covered with craters. There is no liquid water on Mercury.
Venus is the second planet from the sun. It is Earth’s neighbor because it is the closest planet to our Earth.
Venus is the hottest planet in the solar system, even though it is farther from the sun than Mercury. It can get as hot as 900°F (480°C) on Venus. The temperature can get this high because Venus has a thick atmosphere. The air around the planet is mostly a gas called carbon dioxide. The carbon dioxide traps the heat from the sun on the planet’s surface. This is called the greenhouse effect. A greenhouse on Earth is designed to trap heat to help plants grow.
Venus is a very dry planet. It is covered with thick clouds. Earth’s clouds contain water but Venus’ clouds contain sulfuric acid. These clouds are so thick that astronomers on Earth cannot see the surface of the planet with their telescopes. There are craters, mountains, volcanoes, and valleys on the surface of Venus.
The third planet from the Sun is Earth, our home. Earth does not get as hot as Venus. The highest temperature recorded on Earth is 135°F (60°C). The lowest recorded temperature is about -125°F (-85°C).
The surface of Earth is similar to the surfaces of Mercury and Venus. Earth is a hard and rocky planet. There are mountains, valleys, volcanoes, and even some craters. Earth is different in some very important ways. Most of the planet is covered with water. Also, the air is made of nitrogen, oxygen, and carbon dioxide. It is just right for us to breathe! Earth is home to people, plants, and animals because it has both water and the right kind of atmosphere.
Earth is our home. It has air for us to breathe and is warm enough for us to live.
Earth has one moon. The moon is our nearest neighbor in the solar system. It follows a path or orbit around Earth, just as Earth follows a path around the sun.
Our moon has mountains and valleys. It is covered with craters. The surface of the moon is rocky and covered with dust. The moon's atmosphere is thinner than Mercury’s! The temperature on the Moon can reach 265°F (130°C). Because there is almost no atmosphere, the temperature can drop to -170°F (-110°C) at night. There is no water on the moon. There is no life on the moon because it has no water and no air.
Mars is the fourth planet from the sun. Mars can get very cold. The temperature can get as low as -200°F (-130°C).
Mars is a hard, rocky planet. The soil on Mars contains iron oxide (rust) which makes the ground looks red. This is why Mars is often called the red planet. Sometimes, the red dust is stirred up by strong winds. These huge dust storms can last for months. Mars has mountains, canyons, volcanoes, and craters. Scientists think that large canyons were formed long ago by water. There is no liquid water on the surface of Mars. There may be frozen water under the surface and ice on the surface in certain coldest places.
Mars has an atmosphere made entirely of carbon dioxide and traces of nitrogen and other gases. Mars has mountains, volcanoes, valleys, canyons, and craters.
Jupiter is the fifth planet from the sun. Because it is so far from the sun, its temperature is only -220oF (-140oC) at the cloud tops. If one looks at Jupiter through a telescope all that can be seen are the tops of the clouds in its atmosphere. These clouds are made of frozen gases such as ammonia and water. These colorful clouds cover the entire planet, making it look white, brown, red, and orange. Jupiter’s Great Red Spot is a storm that has been going on for over 300 years.
Not only is Jupiter the largest planet in our solar system, but it also has the thickest atmosphere. It is made up of gases such as hydrogen (about 90%), and helium (about 10%). There are also small amounts of ammonia, sulfur, methane, and water vapor. The two dominant gases on Jupiter (hydrogen and helium), happen to also be the gases that make up the sun. It is very cold on Jupiter because it is so far from the sun.
Jupiter has at least 67 known moons. The largest four are called Io, Europa, Ganymede, and Callisto. These four moons are called the Galilean satellites because they were first seen in 1610 by the astronomer Galileo Galileo. Ganymede is the largest moon in the Solar System, with a diameter of 3,260. It has a lot of active volcanoes and is covered with sulfur. Volcanoes on Earth erupt lava, but the volcanoes on Io seem to erupt liquid sulfur. Callisto may have a water ocean beneath its heavily cratered icy, rocky surface. Europa, which is covered by a cracked, icy surface, may also have a liquid water ocean. The other moons are smaller and have irregular shapes. Most of these small moons are thought to be asteroids that were caught by Jupiter's strong gravity.
Saturn is the sixth planet from the sun. It is a lot like Jupiter. Saturn is the second-largest planet in the solar system after Jupiter. It is only slightly smaller than Jupiter in diameter but is much smaller in mass. Overall, Saturn is the least dense planet in the solar system. It is the only planet that is less dense than water, meaning it would actually float on a (huge) ocean of water.
The temperature at Saturn’s cloud tops is -285°F (-175°C). These clouds are made of frozen gases such as ammonia and water. Saturn’s cloud is not as colorful as those covering Jupiter.
Saturn’s atmosphere is similar to Jupiter’s atmosphere. It is mainly made up of two gases – hydrogen and helium.
Saturn has the most spectacular rings in the solar system. Saturn's rings are made up of mostly ice particles with some dust and rocks as well. There are billions of these particles and they vary in size from specks of dust to rocks as big as a bus. Even though these rings stretch out far beyond Saturn’s cloud tops, they are probably less than 100 feet (30m) thick!
Saturn's largest moon is Titan. Titan is the second-largest moon in the Solar System after Jupiter's moon, Ganymede. It is larger than some planets. Titan is the only moon in the Solar System that has a dense atmosphere. Titan has an atmosphere of nitrogen and methane. It was discovered by Dutch astronomer Christian Huygens in 1655. We have never seen the surface of Titan because its sky is filled with a haze similar to smog.
Saturn is very different from Earth. You couldn't stand on the surface of Saturn as its surface is hydrogen gas. Saturn's day of 10.7 hours is much shorter than Earth's while Saturn's year is over 29 Earth years. Saturn is also much, much bigger than Earth and Saturn has 60 moons vs. Earth's 1 moon. In addition, Saturn is unique from all the planets in the Solar system with its highly visible and gigantic rings.
Uranus is the seventh planet from the sun. Uranus is the third-largest planet in the Solar System. Uranus is the only planet named after a Greek god rather than a Roman god. Uranus was the Greek god of the sky and was married to Mother Earth. Uranus was first called a planet by British astronomer William Herschel. Herschel discovered Uranus by using a telescope. Prior to Herschel, Uranus was thought to be a star.
It is possible to see Uranus with the naked eye. Uranus has rings like Saturn, but they are thin and dark.
It is more than twice as far from the Sun as Saturn. Uranus is an ice giant like its sister planet Neptune. Although it has a gas surface, like the gas giants Jupiter and Saturn, much of the interior of the planet is made up of frozen elements. As a result, Uranus has the coldest atmosphere of all the planets in the Solar System.
When astronomers look at Uranus through a telescope they see some clouds and the atmosphere above the clouds. These clouds are made of frozen methane. Methane is a gas that we use for cooking and heating on Earth. The temperature at the top of the clouds is -370°F (-220°C). The clouds of Uranus appear bluish-green because of the methane gas in the atmosphere above them. The atmosphere below the clouds is mainly made of hydrogen and helium.
It's a gas giant, meaning its surface is gas, so you couldn't even stand on it. Being so much further from the Sun, Uranus is much, much colder than Earth. Also, Uranus' odd rotation in relation to the Sun gives it very different seasons. The Sun would shine on parts of Uranus for as long as 42 years and then it would be dark for 42 years.
Some of the moons of Uranus are - Puck, Miranda, Ariel, Umbriel, Titania, and Oberon.
Neptune is the eighth and furthest planet from the sun. Neptune's atmosphere gives it a blue color which is fitting with it being named after the Roman god of the sea. Neptune is slightly smaller than its sister planet Uranus making it the 4th largest planet. However, Neptune is a little bit larger in mass than Uranus making it the 3rd largest planet by mass.
Neptune is an ice-giant planet. This means it has a gas surface like the gas giant planets, but it has an interior composed mostly of ice and rock. The clouds of Neptune are made of frozen methane. These clouds appear blue because of the methane in the atmosphere above the clouds. The atmosphere below the clouds is mainly made of hydrogen and helium. Neptune has a Great Dark Spot. This is probably a storm similar to the Great Red Spot on Jupiter. The center of Neptune may be a core of ice and rock.
Neptune has 13 known moons. The largest of Neptune's moons is Triton. Neptune also has a small ring system similar to Saturn, but not nearly as large or as visible.
Since Neptune is a gas giant planet, there is no rocky surface to walk around on like Earth. Also, Neptune is so far away from the Sun that, unlike Earth, it gets most of its energy from its inner core rather than from the Sun. Neptune is much, much bigger than Earth. Even though much of Neptune is gas, its mass is 17 times that of Earth's.
Asteroids are chunks of rock and metal in outer space that are in orbit around the Sun. They vary in size from just a few feet across to hundreds of miles in diameter. Most asteroids are not round but are lumpy and shaped like a potato.
The word asteroid comes from a Greek word meaning "star-shaped."
The majority of asteroids orbit the Sun in a ring called the asteroid belt. The asteroid belt is located between the planets Mars and Jupiter. You can think of it as a belt between the rocky planets and the gas planets. There are millions and millions of asteroids in the asteroid belt.
Asteroids are of interest to scientists because they are made of some of the same materials that make up the planets. There are three main types of asteroids based on what type of elements make up the asteroid. The main types include – carbon, stony and metallic.
Some asteroids are so large that they are considered minor planets. The four largest asteroids are Ceres, Vesta, Pallas, and Hygiea.
There are other groups of asteroids outside the asteroid belt. One major group is the Trojan asteroids. Trojan asteroids share an orbit with a planet or a moon. However, they don’t collide with the planet. The majority of the Trojan asteroids orbit the sun with Jupiter. Some scientists think there may be as many Trojan asteroids as there are asteroids in the belt.
Many asteroids have struck Earth. These asteroids are called Near-Earth asteroids and they have orbits that cause them to pass close to the Earth. It is estimated that an asteroid larger than 10 feet across strikes the Earth around once a year. These asteroids usually explode when they hit the Earth’s atmosphere and cause little damage to the Earth’s surface.
Comets are lumps of ice, dust, and rock that orbit the Sun. The typical comet has a core that is a few kilometers in diameter. They are often called the “dirty snowballs” of the solar system.
As a comet nears the Sun its ice will begin to heat up and turn into gases and plasma. These gases form a large glowing “head” around the comet that is called a “coma”. As the comet speeds through space, the gases will trail behind comet-forming a tail. Because of their coma and tail, comets appear fuzzy as they near the Sun. This allows astronomers to easily determine comets from other space objects. Some comets can be seen with the naked eye as they pass by Earth.
Comets are usually divided into two groups determined by the type of orbit they have:
Scientists believe that much beyond the Kuiper belt there is another collection of billions of comets which is known as the Oort cloud. This is where long-orbit comets come from. The outer limit of the Oort cloud defines the outer boundary of the solar system.
One of the most famous comets is Halley’s Comet. Halley’s Comet has an orbit of 76 years and is visible from Earth as it passes by.
A meteoroid is a small piece of rock or metal that has broken off from a comet or an asteroid. Meteoroids can form from asteroids colliding or as debris from comets speeding by the sun. Meteors are meteoroids that get pulled into Earth’s atmosphere by Earth’s gravity. When a meteor hits the atmosphere it will heat up and burn with a bright streak of light called a “falling star” or a “shooting star”. If several meteors occur at the same time and near the same place in the sky, it is called a meteor shower. A meteorite is a meteor that does not entirely burn up and makes it all the way to the ground.
