Did you know that you can see five planets from Earth without a telescope or binoculars? In fact, not all of the bright objects that you see in the night sky are stars, some are actually planets! What about the Sun? Is it a planet or a star? In this lesson we are going to explore our space and learn all about the planets and the Solar System.
What is the Solar System?
The solar system is a huge space that consists of the Sun, the planets, and other objects. Other objects in the solar system include moons, comets, asteroids, dwarf planets, dust and gas. All planets and objects in the solar system orbit, or travel around, the Sun. However, most of the solar system is empty space even with all these objects.
The solar system itself is part of a galaxy called the Milky Way. A galaxy is a huge system of stars, gas, dust and other objects that are held together by a pulling force called gravity. The solar system with all its objects orbits the centre of the Milky Way galaxy. The universe is in fact made up of billions of galaxies that were formed billions of years ago when the universe began.
How the Solar System Formed
The solar system was formed about 4.7 billion years ago. Scientists think that it started as a cloud of gas and dust, then gravity pulled parts of the cloud together into clumps. The gravity pressed the largest clump so tightly until it got so hot. This clump then became the Sun. The other clumps became planets over millions of years. The powerful gravity of the Sun pulled the planets and made them orbit the Sun. Some of the leftover clumps became asteroids, comets and other objects in the solar system.
The Sun is the star at the centre of the solar system and the largest object in it. It is a hot ball of gases, mainly hydrogen and helium, and it gives off a great amount of energy. It is around 4.5 billion years old. The Sun’s diameter is 1,392,000 kilometres (865,000 miles). The Sun alone contains about 99% of all the material in the solar system. The temperature at the Sun’s core is more than 15,600,000° C (28,080,000° F). All planets, comets, and asteroids in the solar system orbit the sun. Life on Earth depends on heat and light from the Sun, and it would not exist without the Sun.
There are eight planets orbiting the Sun in the solar system. These planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. If you can’t remember the correct order, try this sentence: “My Very Easy Method Just Speeds Up Naming.” Let’s explore each planet in detail!
Mercury is the closest planet to the Sun, and the smallest planet in the solar system. It orbits the Sun faster than any other planet does. Mercury is a rocky planet that looks much like our moon, and it has so many craters. It completes one orbit around the Sun every 88 Earth days, and it takes around 59 Earth days to complete one rotation about its centre. Mercury has no moons.
Venus is the second planet from the Sun, and the closest planet to Earth. It is also the brightest object in the night sky as seen from Earth. Venus is the hottest planet in the solar system even though it is not the closest to the Sun because it has a thick atmosphere.
Venus is about the same size and weight as Earth, yet it is only slightly smaller. It is a rocky planet. Its surface contains so many volcanoes. Venus takes 225 Earth days to complete one orbit around the Sun, and it takes 243 Earth days to complete one rotation about its centre. It has the slowest rotation of any other planet. Like Mercury, Venus has no moons.
Earth is the planet that we live on, and it is the only living planet in the solar system. It is the third planet from the Sun, between Venus and Mars, and the fifth largest planet in the solar system. Earth is a rocky planet, and it is the largest one among the rocky planets.
The surface of Earth is either water or land. Water covers about 70% of Earth’s surface. The other 30% of Earth’s surface is covered with land. There are layers of gases surrounding Earth called the atmosphere. The atmosphere helps maintain temperatures on Earth so that they are warm enough for us to survive. Earth completes one orbit around the Sun in 365 days, and it completes one rotation about its centre in 24 hours. There is only one moon orbiting Earth called the Moon.
The Moon is the only natural satellite, or moon, that orbits Earth. It takes the Moon about 27 days to complete one orbit around Earth. It takes the same time, too, to rotate about its centre. The Moon is the second brightest object in our sky after the Sun, and the brightest one at night. However, it does not produce its own light but it only reflects light from the Sun.
Most of the Moon’s surface is rock. It is also covered with craters and dead volcanoes. Temperatures on the Moon vary from super hot to super cold because it has no atmosphere. The forces of gravity between the Earth and the Moon cause some interesting effects, such as the ocean tides. The Moon is the only object in space that has been visited by humans.
Mars is the fourth planet from the Sun, between Earth and Jupiter. It is the second smallest planet in the solar system, after Mercury. In fact, Mars is about half the size of Earth. It can be seen from Earth without telescopes or binoculars. Mars is called the “Red Planet” because its colour is red.
Mars is simply a cold desert. It is a rocky planet with complex terrain on its surface, such as mountains and volcanoes. It has a thin atmosphere, so temperatures on Mars change between highs and lows. Scientists believe that there might have been water on Mars a long time ago. Mars completes one orbit around the Sun in 687 Earth days. It rotates about its centre in 24 hours and 37 minutes. Humans have sent many spacecrafts to explore Mars, but humans themselves have not been to Mars yet. Mars has two tiny moons named Phobos and Deimos.
Jupiter is the fifth planet from the Sun, between Mars and Saturn, and the largest planet in the solar system. It is so huge that it could easily swallow all of the other planets. It is a gas giant planet, and it is actually very similar to a star. It consists entirely of gases, mainly hydrogen and helium, which means that it has no solid surface. Jupiter is the third brightest object in the sky, after the Moon and Venus.
Jupiter’s vivid colours are probably a result of chemical interactions in its huge and thick atmosphere. The most interesting feature of Jupiter is a spot called “The Great Red Spot,” which is actually a huge storm. It takes Jupiter about 12 Earth years to complete an orbit around the Sun, and less than 10 hours to complete a rotation about its centre. Scientists think that Jupiter has 79 known moons until now. It also has 3 ring systems surrounding it, but they are thin and hard to see.
Saturn is the sixth planet from the Sun, between Jupiter and Uranus, and it is the second largest planet in the solar system, after Jupiter. Like Jupiter, Saturn is a gas giant planet that is made up of gases, mostly hydrogen and helium. This means that it does not have a solid surface. Its atmosphere is huge, and it consists of gases.
Saturn is most famous for the beautiful rings surrounding it. Those rings are thin and bright, and they can be seen from Earth with a telescope. Saturn has 82 moons, 53 of which are known and named, and the other 29 are awaiting confirmation. Saturn completes an orbit around the Sun in about 29 Earth years, and it completes a rotation about its centre in 10.7 hours.
Uranus is the seventh planet from the Sun, between Saturn and Neptune, and it is the third largest planet in the solar system. It is a gas giant planet, meaning that it consists of gases, and it does not have a solid surface. The atmosphere of Uranus is the coldest atmosphere in the solar system. It contains a gas called methane, which gives the planet a bright blue colour.
Uranus completes an orbit around the Sun in about 84 Earth years. It completes one rotation about its centre in about 17 hours. There are 13 rings surrounding Uranus, but they are not as bright as Saturn’s rings. Scientists have also confirmed 27 moons orbiting Uranus until now. All of those moons are small.
Neptune is the eighth, and the farthest, planet from the Sun, which makes Uranus its only neighbour. It is a gas giant planet, meaning that it is made up of gases, mainly hydrogen and helium, and it does not have a solid surface. It is the fourth largest planet in the solar system, and the smallest one among the gas giants. Neptune is very similar to Uranus in terms of size, mass and composition. So, they are referred to as twin planets, or, sometimes, ice giants. Neptune is a dark, cold and stormy world.
Neptune’s atmosphere is thick and windy. In fact, Neptune’s winds are the fastest and the wildest in the solar system; they could reach up to 2000 km per hour. Sometimes huge storms cause dark spots to form in the atmosphere. Because it is very far from the Sun, temperatures on Neptune are extremely low. Neptune completes an orbit around the Sun in about 165 Earth years, and a rotation about its centre in about 16 hours. Neptune has 14 known moons orbiting it. It also has 6 narrow rings surrounding it, but they are faint.
Dwarf planets are objects in the solar system that are similar to the eight planets but smaller than them, and they orbit the Sun. According to the International Astronomical Union (IAU), to name an object “a planet” it must orbit the Sun, be massive enough for its gravity to pull it into a spherical shape, and clear the area of its orbit from any debris. If a planet has failed to do so, they consider it a dwarf planet instead. Currently, there are five confirmed dwarf planets in the solar system, which are Pluto, Eris, Makemake, Haumea, and Ceres. In fact, there may be more dwarf planets that are not confirmed yet.
Pluto is the largest dwarf planet and the ninth largest object that orbits the Sun in the solar system. It is located beyond Neptune in an area called the Kuiper Belt. Pluto was discovered in 1930 and was considered the ninth planet in the solar system. However, in 2006, the IAU decided that it should be considered a dwarf planet instead. It is in fact the first object to be classified as a dwarf planet.
Pluto is smaller than Mercury, and even smaller than Earth’s Moon. Pluto’s surface consists of rock and frozen gases. Pluto is so far away from the Sun, so it is very cold and dark as it receives so little sunlight. It completes an orbit around the Sun in 248 Earth years, and it completes a rotation about its centre in about 6.5 Earth days. Pluto has five known moons named Charon, Styx, Nix, Kerberos, and Hydra.
Asteroids are small chunks of metal and rock that orbit the Sun in the solar system. Scientists believe that these asteroids are debris left over from collisions between larger objects in the solar system. Most asteroids are less than hundreds of miles in diameter. From time to time, small asteroids fall to Earth or burn up in the sky forming glowing meteors. There are millions of asteroids in the solar system, most of which are found between Mars and Jupiter.
Comets are small chunks of ice and dust that orbit the Sun in the solar system. There are billions of comets in the solar system, but they are actually so small and far away to be seen from Earth. Their orbits are shaped like long ovals. Most comets take several years or even thousands of years to complete one orbit around the Sun. Sometimes dust from comets crash into the atmosphere of Earth which causes them to burn up in the sky and create a meteor shower. Comets come from two regions in the outer solar system, which are the Kuiper Belt and the Oort Cloud.
The Kuiper Belt
The Kuiper Belt is a very distant area in the outer solar system beyond Neptune. It contains countless small, icy bodies that orbit the Sun. The most famous object in the Kuiper Belt is dwarf planet Pluto. The Kuiper Belt also contains millions of comets.
The Oort Cloud
Scientists believe that the Oort Cloud is a region in the outer solar system even beyond the Kuiper Belt. It is a huge cloud that contains trillions of comets and icy objects. It surrounds the outside of the solar system. Scientists believe that most long-period comets in the solar system come from the Oort Cloud.
45 Interesting Facts about Planets for Kids
- Mercury is the second densest planet in the solar system, after Earth, even though it is so small.
- Sunlight takes about 3.2 minutes to travel from the Sun to Mercury.
- Mercury is bright and it can be seen from Earth without a telescope.
- Although Mercury is the closest planet to the Sun, it is not the hottest planet. The hottest planet in the solar system is Venus.
- Venus and Mercury are the only planets in the Solar System that do not have any moons.
- Venus can be seen with the naked eye from Earth without a telescope.
- Venus shines so bright because it reflects most of the sunlight that it receives from the Sun.
- A space journey from Earth to Venus takes 6 months long.
- Any spacecraft sent to Venus survives only for around an hour because of the hot temperatures.
- Venus is the planet that has the most volcanoes in the solar system. It has more than 1600 volcanoes, and some of them are active.
- Scientists call the distance between the Sun and Earth an “astronomical unit.” This unit is used to measure and compare great distances in space.
- Without the atmosphere of Earth, oceans would freeze and there wouldn’t be life on Earth anymore.
- Sunlight takes about 8 minutes to travel from the Sun and reach Earth.
- Earth’s moon is the fifth largest moon in the solar system.
- A spacecraft takes about 3 days to travel from the Earth to the Moon.
- Earth is so compact that it is actually the densest planet in the solar system.
- The Moon rises from the east and sets from the west, just like the Sun.
- The Moon is shaped like an egg.
- Most scientists believe that there is water on the Moon, but they are still researching.
- Earth’s moon is simply called “the Moon” because people did not know any other moons until 1610 when Jupiter’s first moons were discovered.
- Mars can be seen with the naked eye from Earth without any telescopes.
- There are pieces of Mars that have fallen on Earth.
- Mars has strong winds, and they are an obstacle for the space crafts that scientists send from Earth.
- Mars has seasons like Earth, but they last longer than they do on Earth.
- Jupiter can be seen from Earth without a telescope.
- Every 13 months, Jupiter comes closer to Earth and becomes very bright in our night sky.
- A space journey from Earth to Jupiter takes around 13 months long.
- Some scientists consider Jupiter a failed star because of its great mass. If Jupiter were 75 times more massive, it would become a star just like the Sun.
- Jupiter generates more heat than it receives from the Sun.
- Saturn is the least dense planet in the solar system that if you could put it in water, it would float.
- Saturn generates more heat than it receives from the Sun.
- The winds on Saturn are the second fastest winds of a planet in the solar system, after Neptune’s winds.
- The day “Saturday” is named after planet Saturn.
- Uranus was the first planet that scientists discovered after the invention of the telescope.
- Uranus can sometimes be seen with the naked eye from Earth, but only on a very clear night sky.
- In 2033, Uranus will complete its third orbit around the Sun since its discovery.
- The moons of Uranus are all dark and frozen.
- The surfaces of the biggest moons of Uranus together are smaller than the continent of Australia.
- Both Uranus and Neptune share similar compositions, so scientists classify them as “ice giants.”
- Neptune is the only planet that cannot be seen from Earth with the naked eye. It can only be seen with the use of a telescope.
- One of Neptune’s moons, called Triton, is the coldest object in the solar system.
- Pluto, Venus, and Uranus rotate from east to west. This is called a retrograde rotation.
- Pluto is tilted, meaning that it rotates almost on its side.
- Pluto passes inside the orbit of Neptune when it comes closer to the Sun.
- Although Pluto is farther from the Sun than Neptune, it gets closer than Neptune to the Sun during its orbit.