Meet our solar system
Understand the Sun’s planetary family and the clues it preserves about formation.
A system held together by gravity
The solar system contains the Sun and the objects gravitationally associated with it, including eight planets, dwarf planets, moons, asteroids, comets, and dust. The Sun contains almost all the system’s mass. It is a star: a hot sphere of plasma that releases energy through nuclear fusion in its core. Planets do not shine by that same process. In visible light, we usually see them because they reflect sunlight. Orbits are paths shaped by gravity and motion; they are not rails or fixed circles printed into space. Most major planets travel in roughly the same orbital plane.
Worlds with different ingredients
Mercury, Venus, Earth, and Mars are the rocky inner planets. Jupiter and Saturn are gas giants, while Uranus and Neptune are commonly called ice giants because of their different bulk compositions. “Ice” here describes important ingredients in planetary formation and does not mean a solid frozen surface that a visitor could stand on. Moons are worlds in their own right, with varied histories and environments. Some have volcanism or evidence for subsurface oceans. A planet’s distance from the Sun matters, but atmosphere, size, composition, and internal energy also influence its conditions.
Small bodies preserve big clues
Asteroids are concentrated in several populations, including the main belt between Mars and Jupiter. Comets contain volatile material that can form a glowing coma and tails when heated near the Sun. The tails do not simply trail behind like a vehicle’s exhaust; sunlight and the solar wind strongly influence their directions. The Kuiper Belt beyond Neptune contains icy objects, including Pluto. Small bodies can preserve material from early solar-system history, although collisions and heating may alter them. Meteorites studied in laboratories provide evidence that connects tiny samples to the larger story of planetary formation.
Read the system as a history
The Sun and planets formed from a cloud of gas and dust about 4.6 billion years ago. A rotating disk surrounded the young Sun, and particles gradually assembled into larger bodies. The final system was shaped by impacts, gravitational interactions, and the movement of material. Think of the present arrangement as the surviving evidence of a construction site after a long, eventful project. It is not a perfect frozen copy of the initial disk. Comparing different worlds lets scientists test ideas about how planets form, why they differ, and whether similar processes operate around other stars.
A small experiment
Choose Earth and one other planet. Compare their materials, atmosphere, and energy sources. Explain why distance from the Sun alone cannot describe both worlds.