The solar system (age 11+)
Describe the detailed structure of the solar system, including moons, asteroids, and comets, compare orbital periods and distances of the planets, and distinguish between planets, dwarf planets, and other bodies
What a learner can do afterwards
- Identifies the eight planets in order from the Sun and matches each to a distinguishing fact
- Describes the difference between a planet, a dwarf planet, an asteroid, and a comet
- Explains that planets farther from the Sun on average have longer orbital periods because their paths are longer and their average orbital speeds are lower
1 · Read
From the Sun outward: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Mercury is smallest; Venus is hottest. Earth has liquid oceans; Mars has a reddish surface. Jupiter is largest; Saturn has bright, wide rings. Uranus spins almost on its side; Neptune is farthest from the Sun. Check each planet claim against these facts, then count the matches. A moon is a natural body orbiting a planet or another small world.
Planet order from the Sun outward. The cells do not show sizes or distances.
A planet orbits the Sun and has enough gravity to become nearly round. It must also dominate its orbital neighborhood. This is called clearing the neighborhood. This does not mean an empty path. A dwarf planet is nearly round, orbits the Sun, and is not a moon, but has not cleared its neighborhood. Pluto and Ceres are dwarf planets; Ceres lies between Mars and Jupiter. Most asteroids are small and irregular.
An orbital period is the time for one orbit. Planetary orbits are slightly stretched loops. Planets farther from the Sun on average have longer paths and lower average orbital speeds, so their years are longer. Mars takes about 1.9 Earth years; Neptune takes about 165. For objects orbiting the Sun, a longer period indicates a larger orbit overall. Distance changes along a stretched orbit, so a period cannot tell you where an object is today.
Asteroids are mostly rocky or metallic bodies. Most orbit between Mars and Jupiter in the asteroid belt. Comets contain ice, dust, and rock. Near the Sun, ice can turn into gas and release dust, forming tails. A distant comet may have no visible tail. Some asteroids also release dust, so a tail alone is not a reliable way to distinguish these bodies.
Planets, dwarf planets, moons, asteroids, and comets have different features. Among the planets, greater average distance from the Sun means a longer orbital period.
Lesson, questions, and flashcards written for this dataset.
Readings and flashcards written for this dataset.
More to read
Compare the lengths of planetary years
A year measures one planet's complete trip around the Sun. Mercury finishes in about 88 Earth days. Neptune needs about 165 Earth years. The outer planet travels a longer path and has a lower average orbital speed. Both affect its year length. Planetary paths are slightly stretched loops, so a planet's distance changes during an orbit. Compare whole orbital periods to learn about orbit size. A single distance measurement does not describe the whole path.
Use materials to describe small bodies
Scientists use more than appearance to describe small bodies. Asteroids are mostly rocky or metallic. Comets contain ice mixed with dust and rock. Near the Sun, escaping gas can carry dust away from a comet and produce tails. Farther away, that comet may have no visible tail. Some asteroids release dust too. Materials and activity together give a better description than a rule saying that every comet has a tail and every asteroid lacks one.
Small bodies hold clues
Asteroids and comets contain material left from the solar system's formation. Their histories differ. Collisions can break an asteroid into fragments, and repeated passes near the Sun can remove a comet's ice. Most asteroids orbit between Mars and Jupiter. Many icy bodies occupy regions beyond Neptune, including the Kuiper belt. Studying their materials helps scientists investigate how the solar system formed. These objects provide evidence from the past, but they have not all stayed unchanged.
Why Pluto is a dwarf planet
Pluto travels around the Sun and is nearly round. It is not a moon. It has not cleared its orbital neighborhood, so it is classified as a dwarf planet rather than one of the eight planets. Pluto belongs to the Kuiper belt. Its tilted, stretched orbit sometimes brings it closer to the Sun than Neptune. Charon, its large moon, is roughly half Pluto's diameter. Having a moon does not determine whether a body is a planet.
Compare named moons
A moon is a natural body orbiting a planet or another small world. Mercury and Venus have no known moons. Earth has one large Moon, while Mars has two small moons called Phobos and Deimos. Io, Europa, Ganymede, and Callisto orbit Jupiter. Titan belongs to Saturn's moon system, and Triton orbits Neptune. Discovery totals change as observations are checked. Comparing named moons avoids treating an old catalogue's total as a current count.
2 · Watch
En anglaisTake it off screen
Where it sits
Learn first
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.