Eight planets, well over 400 moons, and one star hold together a family of worlds bound by gravity. This article maps out the Sun, the planets, and the smaller bodies that share our cosmic neighbourhood.
Every planet you can name, every moon that circles them, and every comet that streaks across the night sky belongs to one gravitationally bound family: the Solar System. At its centre sits a single star whose gravity and light make everything else possible. This article walks through the Sun, the eight planets, their moons, and the smaller worlds that fill in the gaps.
The Solar System is the Sun together with everything that orbits it because of its gravity: eight planets, their moons, five recognised dwarf planets, and countless asteroids, comets, and smaller fragments of rock and ice. It formed about 4.6 billion years ago from a huge, slowly spinning cloud of gas and dust that collapsed under its own gravity.
Almost everything in the Solar System orbits the Sun in roughly the same flat plane and in the same direction, a pattern left over from that original spinning cloud. The planets are grouped into two families based on their distance and composition:
If the Sun were shrunk to the size of a basketball, Earth would be a peppercorn orbiting about 26 metres away — roughly the length of a school corridor — and Neptune would be a small pea nearly 800 metres away. The Solar System is mostly empty space.
The Sun is a medium-sized star made almost entirely of hydrogen and helium. It holds about 99.8% of all the mass in the Solar System, which is why its gravity controls the orbits of everything else. Deep in its core, temperatures reach around 15 million°C, hot and dense enough for nuclear fusion to turn hydrogen into helium, releasing the light and heat that reach Earth about eight minutes later.
The Sun's visible surface, called the photosphere, is a comparatively cool 5,500°C. Above it lies the corona, a wispy outer atmosphere that is, surprisingly, far hotter than the surface itself — a puzzle scientists are still investigating.
Solar flares and eruptions from the Sun's surface can send charged particles toward Earth. When they interact with our atmosphere near the poles, they produce the shimmering lights known as auroras. Strong solar activity can also disrupt satellites and power grids, which is why space agencies track the Sun's activity daily.
The four planets closest to the Sun are small, dense, and have solid rocky surfaces. Each one is strikingly different from its neighbours.
| Planet | Distance from Sun | Notable Feature |
|---|---|---|
| Mercury | Closest, 1st | Smallest planet; extreme temperature swings with no real atmosphere to trap heat |
| Venus | 2nd | Hottest planet due to a thick, heat-trapping carbon dioxide atmosphere |
| Earth | 3rd | Only known planet with liquid water on its surface and life |
| Mars | 4th | The "Red Planet," coloured by iron oxide (rust) in its soil |
Despite being closer to the Sun, Mercury is not the hottest planet — Venus is. Mercury has almost no atmosphere to hold in heat, so its surface temperature swings wildly between day and night, while Venus's dense atmosphere traps heat constantly, similar to an extreme greenhouse effect.
Beyond Mars lies the asteroid belt, and beyond that, the four outer planets — far larger than the inner four, and built from gas and ice rather than rock.
| Planet | Type | Notable Feature |
|---|---|---|
| Jupiter | Gas Giant | Largest planet in the Solar System; the Great Red Spot is a storm wider than Earth |
| Saturn | Gas Giant | Famous for its wide, bright rings made of ice and rock particles |
| Uranus | Ice Giant | Rotates almost on its side, likely due to an ancient collision |
| Neptune | Ice Giant | Windiest planet, with storms reaching over 2,000 km/h |
All four giant planets have ring systems, but Saturn's are by far the most visible from Earth. Its rings are made of countless chunks of ice and rock, ranging from dust-sized grains to boulders, all orbiting in a disc thousands of kilometres wide but often less than a kilometre thick.
A moon is any natural object that orbits a planet. Rocky Mercury and Venus have none at all, Earth has one, Mars has two tiny moons (Phobos and Deimos), and the giant planets each have dozens — Jupiter and Saturn alone account for well over 200 known moons combined.
Not every round object orbiting the Sun qualifies as a full planet. A dwarf planet orbits the Sun and is round due to its own gravity, but unlike a full planet, it has not cleared other debris from the area around its orbit. Five dwarf planets are currently recognised: Pluto, Eris, Haumea, Makemake, and Ceres.
Beyond these are two major reservoirs of smaller bodies:
Pluto was classified as the ninth planet from 1930 until 2006, when astronomers set a formal definition of "planet" that Pluto did not meet, reclassifying it as a dwarf planet instead.
The Solar System is a single gravitational system built around one star, but it holds an astonishing range of worlds — scorching, frozen, stormy, and, on at least one planet, alive. Understanding how these pieces fit together is the foundation for exploring everything else in space science.
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