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The Solar System for Kids: Planets, Facts and Activities
Our solar system is the Sun and everything that travels around it: eight planets, their moons, dwarf planets, asteroids and comets. Learning about it is a great way to bring up scale, gravity and the scientific method with kids of many ages.
The Sun
The Sun is a star, a giant ball of hot gas that makes light and heat through nuclear fusion. It holds about 99.8 percent of all the mass in the solar system, and its gravity keeps everything in orbit. Sunlight takes about 8 minutes to reach Earth. Safety note: never look directly at the Sun, even briefly, and never use ordinary sunglasses for solar viewing.
The eight planets in order from the Sun
A popular memory sentence is "My Very Eager Mother Just Served Us Noodles" (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune).
| Planet | Type | Fun fact |
|---|---|---|
| Mercury | Rocky | Smallest planet and closest to the Sun. One year is only 88 Earth days. |
| Venus | Rocky | Hottest planet (around 465°C or 870°F) because its thick atmosphere traps heat. It spins backward compared with most planets. |
| Earth | Rocky | The only known planet with life and liquid water on its surface. About 71 percent of the surface is ocean. |
| Mars | Rocky | Called the Red Planet because of iron oxide (rust) in its soil. Has the tallest volcano in the solar system, Olympus Mons. |
| Jupiter | Gas giant | The largest planet; more than 1,000 Earths could fit inside. Its Great Red Spot is a giant storm. |
| Saturn | Gas giant | Famous for bright rings made mostly of ice particles. It is so light for its size that, on average, it is less dense than water. |
| Uranus | Ice giant | Tilted on its side, so it seems to roll around the Sun. |
| Neptune | Ice giant | The farthest planet, with very strong winds. One orbit around the Sun takes about 165 Earth years. |
Inner planets and outer planets
The four inner planets (Mercury, Venus, Earth, Mars) are small and rocky, with solid surfaces. The four outer planets are much larger. Jupiter and Saturn are mostly hydrogen and helium; Uranus and Neptune contain more icy materials such as water, ammonia and methane. Between Mars and Jupiter lies the asteroid belt, a region of rocky leftovers from the early solar system.
What happened to Pluto?
Pluto was called the ninth planet from 1930 until 2006. That year the International Astronomical Union defined a planet as an object that orbits the Sun, is round, and has cleared its orbit of other objects. Pluto has not cleared its path, so it is now classified as a dwarf planet. It is a good example of how science changes when scientists learn more.
Day, year and seasons
A day is the time a planet takes to spin once on its axis (about 24 hours on Earth). A year is the time to orbit the Sun once (about 365 days on Earth). Earth has seasons because its axis is tilted about 23.5 degrees, so different parts get more direct sunlight at different times of the year. Distance from the Sun does not cause the seasons.
Activities to try at home
- Scale walk: mark planets along a hallway or sidewalk using a roll of toilet paper, one square per ten million miles or another scale. Kids are always surprised by how empty space is.
- Day and night: shine a flashlight on a ball in a dark room and spin the ball slowly.
- Moon journal: draw the shape of the Moon each evening for a month and look for patterns.
- Build a model: use clay, paper plates or fruit to build planets in proportion.
- Stargazing: Venus, Jupiter, Mars and Saturn can often be seen with the naked eye. Use a free sky map app to find them.
Practice quiz
- Which planet is closest to the Sun?
- Which planet is known as the Red Planet?
- Name the largest planet.
- Which planet has the most famous rings?
- Is the Sun a planet, a moon or a star?
- What is Pluto classified as today?
- About how long does it take sunlight to reach Earth?
- Which two planets are called gas giants?
Answer key
1) Mercury 2) Mars 3) Jupiter 4) Saturn 5) A star 6) A dwarf planet 7) About 8 minutes 8) Jupiter and Saturn
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