How Does the Solar System Work?
Eight planets, one star, and the invisible force that holds it all together.
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.
Light from the Sun takes about 8 minutes to reach Earth — but over 4 hours to reach Neptune. If you could drive a car at highway speed to the Sun, it would take over 170 years. Our solar system is almost incomprehensibly vast, and yet it's a tiny speck compared to our galaxy, which contains hundreds of billions of other star systems.
Last reviewed: April 2026