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A planet is a large object such as Jupiter or Earth that orbits a star. It is smaller than a star, and it does not make light. Planets are ball-shaped spheres. Objects that orbit planets are called moons. There are eight planets in the Solar System, but there used to be nine until Pluto’s classification changed.
See the fact file below for more information about key solar system planets, or alternatively, download our comprehensive worksheet pack to utilize within the classroom or home environment.
What is a planet?
- A planet is a large astronomical object that is not a star.
- It is a celestial body inside the Solar System that orbits around the Sun.
- Astronomical means relating or belonging to the science of astronomy.
- Astronomy is a natural science that studies astronomical (sometimes called celestial) objects.
Facts About Planets
- The term planet is ancient, with ties to history, astrology, science, mythology, and religion.
- The definition of a planet versus other objects orbiting the Sun has changed many times.
- In ancient times, astronomers noted how certain lights moved across the sky, as opposed to stationary stars, which maintained a constant position in the sky.
- The invention of the telescope enabled the discovery of many more planetary objects, diverse in size, shape, and orbit.
- As scientific knowledge advanced, human perception of the planets changed.
- All eight planets can be seen with a small telescope or binoculars.
- It is not known with certainty how planets are formed.
- Scientists think planets start off as grains of dust smaller than the width of a human hair.
- They emerge from the giant, donut-shaped disk of gas and dust that circles young stars.
- Gravity and other forces cause material within the disk to collide.
- If the collision is gentle enough, the material fuses, growing like rolling snowballs.
- Over time, dust particles combine to form pebbles, which evolve into mile-sized rocks.
- This process takes place over billions of years.
- The eight Solar planets are divided into two types:
- Large low-density giant planets
- Small rocky terrestrial plants
- The four giant planets are Neptune, Uranus, Saturn, and Neptune.
- The four terrestrial planets are Earth, Mars, Mercury, and Venus.
- Over 5,000 extrasolar planets have been discovered. More than 100 of these planets are approximately the same size as Earth.
- In 1930 the planet Pluto was discovered. Initially, it was believed to be larger than Earth and was accepted as the ninth major planet. Further investigation found it was actually much smaller, so it is no longer recognized as the ninth planet.
Planet Rotation
- Planets rotate around invisible axes through their centers.
- The planet’s rotation period is known as a “stellar day”.
- Most planets rotate in the same direction as they orbit the Sun, which is counter-clockwise.
- Venus and Uranus are the exceptions as they rotate clockwise.
The planets, in order of size from largest to smallest, are:
Jupiter
- Jupiter is the largest planet in the Solar System.
- It is also the fifth planet from the Sun.
- This planet is huge, approximately 11 times larger than Earth.
- It is actually more than two and a half times that of all the other planets in the Solar System combined.
- Its average diameter is 139822 km (86881 mi)
- Jupiter’s familiar stripes and swirls are actually cold, windy clouds of ammonia and water, floating in an atmosphere of hydrogen and helium.
- Jupiter’s Great Red Spot is a giant storm that has raged for hundreds of years.
- The Romans named this planet after their king of gods, who was also the god of the sky and of thunder.
- Jupiter has 63 moons.
Saturn
- Saturn is the second-largest in the Solar System.
- It is the sixth planet from the Sun.
- Its average diameter is 116464 km (72367 mi), about nine and a half times that of Earth.
- Saturn is a massive ball made mostly of helium and hydrogen.
- Saturn is unique among the planets as it is adorned with thousands of beautiful ringlets.
- Saturn was named after the Roman god of agriculture.
- Saturn has 33 moons.
Uranus
- Uranus is the third-largest planet in our solar system.
- Uranus is almost four times larger than our Earth.
- Its average diameter is 50724 km (31518 mi).
- Uranus was discovered in 1781 by astronomer William Herschel who originally thought it was a star or a comet. It was only accepted as a planet two years later.
- It was the first planet found with the aid of a telescope.
- Uranus orbits while lying on its side because its axis is at 97 degrees.
- Uranus was named after an ancient Greek god of the sky.
- Uranus has 21 moons.
Neptune
- Neptune is the fourth-largest planet by diameter and the densest giant planet
- It is the farthest Solar planet from the Sun.
- It is 17 times the mass of Earth.
- Its average diameter is 49244 km (30599 mi).
- Neptune was named after the Roman god of the sea.
- Neptune has 13 moons.
Earth
- Earth is the largest terrestrial planet in the solar system.
- It is the fourth-smallest planet and only a little larger than planet Venus.
- Its average diameter is 12742 km (7917.5 mi)
- Earth is over 4 billion years old and is the only planet known to harbor life.
- Although large volumes of water can be found throughout the Solar System, only Earth has surface water. About 71% of Earth’s surface is made up of the ocean.
- Earth is the only planet that was not named after a Greek or Roman god or goddess.
- Earth has only 1 moon.
Venus
- Venus is the second planet from the Sun.
- It is named after the Roman goddess of love and beauty.
- Venus is only just a little smaller than Earth. Because its size nearly matches that of Earth, Planet Venus is also known as Earth’s sister.
- Its average diameter is 12104 km (7521 mi)
- Venus is the brightest natural object in Earth’s night sky after the Moon.
- Venus is the hottest planet due to the number of greenhouse gasses in the atmosphere.
- Venus has no moons.
Mars
- Mars is the second-smallest planet in the Solar System
- It is the fourth planet from the Sun.
- Mars is named after the Roman god of war.
- It has been extensively explored.
- Mars has seasons, polar ice caps, canyons, and extinct volcanoes.
- It gets its red color from iron oxide in its soil.
- It is dusty and cold, with a very thin atmosphere.
- Its average diameter is 12104 km (7521 mi)
- Mars has the largest volcano in our solar system, and it is almost 17 miles high.
- Mars also has 2 moons.
Mercury
- Mercury is the smallest planet in the Solar System
- It is also the closest planet to the Sun.
- Mercury was named after the Roman god Mercurius
- It is just 0.38 times the Earth and is just a little larger than our Moon.
- Its diameter is 4880 km (3032 mi)
- Mercury’s orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun’s planets.
- Mercury has no moons.
Did You Know?
- The Sun is a star, not a planet, and it is also the largest object in our solar system.
- The diameter of the Sun is around 109 times the diameter of Earth.
- It measures 1,392,680 km (865,371 mi).
- By volume, the Sun is approximately 1,300,000 times bigger than Earth. This means that about 1,300,000 Earth-size objects could fit inside the Sun.
Planet Worksheets
This bundle contains 12 ready-to-use planet worksheets that are perfect for students who want to learn more about the solar system and the eight planets within it.
Download includes the following worksheets:
- Planets Facts.
- Planet Labels.
- Planets Wordsearch.
- Jupiter’s Eye.
- Planet Factfile.
- Fill-in-the-Blanks.
- Planets Crossword.
- Guess the Planet.
- Unscramble the Planet.
- Should Humans Colonize Mars?
- Write a Postcard.
- BONUS Hidden Planet Activity!
Frequently Asked Questions
Is the Moon a planet?
No, the Moon is not a planet, but it functions as a planet. The Moon is a natural satellite that rotates around both the Sun and the Earth.
How many planets orbit the Sun?
Eight planets orbit around the Sun.
Is there life on all the planets?
Earth is the only planet that we know that has creatures living on it.
Which is the largest planet?
Jupiter is the largest planet in the solar system. It is bigger than all the other planets put together.
Which is the coldest planet?
The coldest planet in our solar system is Uranus. It is about 20 times further away from the Sun than the Earth is.
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Link will appear as Planet Facts & Worksheets: https://kidskonnect.com - KidsKonnect, September 26, 2017
Use With Any Curriculum
These worksheets have been specifically designed for use with any international curriculum. You can use these worksheets as-is, or edit them using Google Slides to make them more specific to your own student ability levels and curriculum standards.