How Does the Solar System Work?

One Star, Eight Planets

Our solar system is a family of objects held together by the gravitational pull of one massive star: the Sun. The Sun contains 99.86% of all the mass in the solar system — everything else (planets, moons, asteroids, comets) makes up that tiny remaining sliver. The Sun's enormous gravity is what keeps all eight planets in orbit, spinning around it like a cosmic carousel.

The eight planets, in order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. A helpful way to remember the order: "My Very Excited Mother Just Served Us Nachos."

The Rocky Inner Planets

The four planets closest to the Sun — Mercury, Venus, Earth, and Mars — are called the terrestrial (rocky) planets. They're relatively small, made of rock and metal, and have solid surfaces you could (theoretically) stand on.

Mercury is the smallest planet and closest to the Sun, with extreme temperature swings: 430°C during the day, -180°C at night. Venus is Earth's "evil twin" — similar in size but with a thick atmosphere of CO₂ that traps heat, making it the hottest planet at 465°C. Earth is the only planet known to have liquid water on its surface and support life. Mars, the Red Planet, has the largest volcano in the solar system (Olympus Mons) and evidence of ancient water.

The Gas and Ice Giants

Beyond Mars, past the asteroid belt, lie the four outer planets. Jupiter and Saturn are gas giants — enormous balls of hydrogen and helium with no solid surface. Uranus and Neptune are ice giants — similar but with more water, ammonia, and methane ice.

Jupiter is the giant of the family: 1,300 Earths could fit inside it. Its Great Red Spot is a storm larger than Earth that has been raging for over 300 years. Saturn is famous for its stunning rings, made of billions of chunks of ice and rock. Uranus rotates on its side (likely knocked over by a collision billions of years ago). Neptune, the farthest planet, has the fastest winds in the solar system — up to 2,100 km/h.

What Keeps Planets in Orbit?

Gravity is the force that holds the solar system together. The Sun's massive gravity pulls on every planet, and each planet's forward motion (inertia) keeps it from falling into the Sun. The balance between gravity pulling inward and motion carrying the planet forward creates an orbit — a curved path that the planet follows around the Sun.

Planets closer to the Sun orbit faster (Mercury takes just 88 days), while distant planets orbit slower (Neptune takes 165 Earth years to complete one orbit). This is because closer planets need more speed to resist the Sun's stronger gravitational pull.

Where Kids Get Stuck

The most persistent misconception is about scale. Textbook diagrams show planets neatly spaced around the Sun, but in reality the solar system is almost entirely empty space. If the Sun were the size of a basketball, Earth would be a small peppercorn about 26 meters away, and Jupiter would be an acorn 135 meters away. Neptune would be over half a kilometer from the basketball. Most models are wildly misleading about how vast and empty space truly is.

Another common confusion is why we have seasons. Many children (and adults) believe seasons happen because Earth is closer to the Sun in summer and farther in winter. This is incorrect — Earth's distance from the Sun varies only slightly, and the Northern Hemisphere is actually closest to the Sun during its winter. Seasons are caused by Earth's 23.5-degree axial tilt, which changes how directly sunlight hits different parts of the planet.

Students also mix up rotation and revolution. Rotation is spinning on an axis (one rotation = one day). Revolution is orbiting around the Sun (one revolution = one year). These are completely different motions happening simultaneously.

What Holds It All Together

Gravity is the invisible force that organizes the entire solar system. The Sun contains 99.86% of all the mass in the solar system, and its enormous gravitational pull keeps all eight planets in orbit. The planets don't orbit in perfect circles — they follow slightly oval paths called ellipses, a discovery by Johannes Kepler in the early 1600s that overturned the ancient belief in perfectly circular orbits.

Every object pulls on every other object. Earth's gravity holds the Moon in orbit, Jupiter's gravity captures asteroids, and the combined gravity of all the planets causes subtle wobbles in each other's orbits. These gravitational interactions make the solar system a dynamic, ever-adjusting system rather than a static model.

Try This at Home

• Scale model walk — Use a basketball for the Sun and pace out the planets at scale. You'll need a large park — the experience of walking "to Neptune" is unforgettable.
• Flashlight seasons — Shine a flashlight at a globe straight-on (summer) and at an angle (winter). This demonstrates why tilt causes seasons.
• Planet size comparison — Use fruits: Sun = exercise ball, Jupiter = grapefruit, Earth = cherry, Mars = blueberry, Mercury = peppercorn.
• Night sky observation — Download a free sky-watching app and identify visible planets. Jupiter and Venus are often the brightest objects in the sky.

For more science ideas, see: Free Science Tools for the Classroom.

🌠 Explore the Solar System Tool

Last reviewed: May 2026