The Solar System
The universe is filled with billions of star systems. Located inside galaxies, these cosmic arrangements are made up of at least one star and all the objects that travel around it, including planets, dwarf planets, moons, asteroids, comets, and meteoroids. The star system we’re most familiar with, of course, is our own.
If you were to look at a giant picture of space, zoom in on the Milky Way galaxy, and then zoom in again on one of its outer spiral arms, you’d find the solar system. Astronomers believe it formed about 4.5 billion years ago, when a massive interstellar cloud of gas and dust collapsed on itself, giving rise to the star that anchors our solar system—that big ball of warmth known as the sun.
Along with the sun, our cosmic neighbourhood includes the eight major planets. The closest to the sun is Mercury, followed by Venus, Earth, and Mars. These are known as terrestrial planets, because they’re solid and rocky. Beyond the orbit of Mars, you’ll find the main asteroid belt, a region of space rocks left over from the formation of the planets. Next come the much bigger gas giants Jupiter and Saturn, which is known for its large ring systems made of ice, rock, or both. Farther out are the ice giants Uranus and Neptune. Beyond that, a host of smaller icy worlds congregate in an enormous stretch of space called the Kuiper Belt. Perhaps the most famous resident there is Pluto. Once considered the ninth planet, Pluto is now officially classified as a dwarf planet, along with three other objects and Ceres in the asteroid belt.