A planet is an astronomical body that orbits a star. Planets are small enough so that nuclear fusion does not take place, rounded by their own gravity, and have cleared planetesimals in their neighboring region.
A planet is a body in space that orbits a star. Earth, Mars, and Neptune are all examples of planets in our solar system. In order to be defined as a planet by the International Astronomical Union (IAU), the body needs to meet three criteria. The first is that the body isn’t so large that nuclear fusion reactions occur in its core. Bodies that are large enough so that fusion reactions take place are more commonly known as stars. The body also needs to be large enough so that its gravitational force has rounded it into a rough sphere shape. Rounding doesn’t occur with asteroids, even though they also orbit the Sun. Finally, the body needs to have cleared all the planetesimals in its neighboring area. There are eight planets in our solar system.
There were nine planets recognized by the IAU until 2006 when Pluto was downgraded from a planet to a dwarf planet. While Pluto meets most of the criteria of being a planet, it hasn’t cleared the neighborhood around its orbit. This means along Pluto’s orbit there are still a large amount of other, smaller objects.
Planets can be divided into two main groups depending on their composition: gas giants and rocky planets. In our solar system, the rocky planets are Mercury, Venus, Earth, and Mars. The gas giants are Jupiter, Saturn, Uranus, and Neptune, although the last two are sometimes also called the ice giants due to their very cold temperatures.
In the 21st century, scientists started to search for extrasolar planets (a.k.a. exoplanets). The first confirmed discovery of a planet outside of our solar system occurred in 1992. Since then, there have been thousands of discoveries of exoplanets in planet systems, with hundreds of systems having more than one planet. Scientists are now becoming more interested in the possibility of life on one of these far away planets. They have found some planets that appear to have similar conditions to Earth.
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Try it for Free!Planets In Our Solar System
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
How Tos about What is a Planet?
Design a hands-on planet model activity for your class
Gather simple materials like styrofoam balls, paint, and string to create a solar system model. Assign each student a planet and guide them to research its colors and features. Hang the models in order from the sun and encourage each student to present their planet's facts to the class.
Integrate planet facts into a cross-curricular lesson
Combine science and language arts by having students write short reports or poems about their favorite planet. Connect research and creativity to deepen understanding and keep learning engaging.
Encourage critical thinking with planet comparison charts
Provide templates for students to compare planet sizes, distances, and characteristics. Discuss why each planet is unique and ask students to share interesting observations.
Organize a planet fact scavenger hunt
Hide planet fact cards around the classroom and let students search for information. Promote movement and engagement as students race to collect facts and share them in small groups.
Use technology to explore planets interactively
Introduce students to virtual tours and planet simulation apps. Encourage exploration of real images and data to make learning about planets vivid and memorable.
Frequently Asked Questions about What is a Planet?
What is a planet?
A planet is a large object in space that orbits a star, is spherical in shape due to its gravity, and has cleared its orbit of other debris. Earth is one example of a planet in our solar system.
How do scientists define a planet?
Scientists define a planet as a celestial body that orbits the Sun, has enough mass for its gravity to make it round, and has cleared its orbital path of other objects. This definition was set by the International Astronomical Union (IAU) in 2006.
What are the differences between a planet and a dwarf planet?
The main difference is that a planet has cleared its orbit of other debris, while a dwarf planet has not. Both are round and orbit the Sun, but only planets meet all criteria set by the IAU.
How many planets are in our solar system?
There are eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto was reclassified as a dwarf planet in 2006.
Why was Pluto reclassified from a planet to a dwarf planet?
Pluto was reclassified because it does not clear its orbit of other objects. According to the IAU's planet definition, this means Pluto is a dwarf planet instead of a traditional planet.
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