The study of the solar system began when early astronomers noticed some stars in the night sky moved much differently than all the others. This led to the discovery of planets, and the geocentric model that the sun, moon, all other planets, and all of the stars orbited the Earth. The heliocentric model, first proposed by Nicolaus Copernicus in the 16th century, placed the sun at the center of the solar system, but this revolutionary idea faced much opposition at the time. About a century later, Johannes Kepler further developed the heliocentric model by coming up with his three laws of planetary motion to describe the orbits of the planets. Isaac Newton furthered Kepler’s laws when he developed the law of universal gravitation. The invention of the telescope allowed astronomers to see farther and discover the planets Uranus and Neptune! The study of the solar system is nowhere near complete, there is still much to learn about the planets, the many moons orbiting those planets, and everything in between and beyond. .

The Planets

There are currently eight known planets in our solar system, in order of proximity to the Sun they are as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. These planets are broken up into two groups, the inner rocky planets (Mercury through Mars), and the outer gas giants (Jupiter through Neptune). Other than the eight main planets, our solar system also has five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris. These dwarf planets are all too small to be classified as regular planets, but big enough and spherical enough to be scientifically significant when studying the solar system (thus they get their own classification, dwarf planets), Beyond these, there exists a theory that there may be a ninth planet, referred to as Planet Nine, that orbits way beyond that of Neptune. Though for now the ninth planet remains only a theory.

Oftentimes planets also have smaller celestial bodies orbiting them as well, these are known as natural satellites, or often referred to as moons! Moons come in many different forms, varying in shape, size, composition, orbit, and more. The most well known moon is of course our moon, which we aptly named “The Moon”. Saturn has the most moons with roughly 150 observed so far! Saturn also is well known for its prominent rings, which are made up of ice, dust, and small rocks. Though Saturn has the most well known rings, all of the other gas giants also have ring systems! Beyond moons and rings there are also Trojans, which are asteroids that essentially share an orbit with a planet either in front of or behind a given planet in a stable lagrange point (specifically L4 or L5).

everthing else

The solar system has much more than just the Sun and its orbiting planets. Just beyond the four inner rocky planets exists the Asteroid Belt. The Asteroid Belt is a ring of asteroids ranging in size from less than a meter wide to nearly 600 kilometers! The Kuiper Belt is similar to the Asteroid Belt, but consists of icy objects (called Kuiper Belt Objects, or KBOs) that orbit in a ring beyond that of Neptune’s orbit. Most of the known dwarf planets exist within the Kuiper Belt! Next is the Oort Cloud, which is a theoretical sphere of icy comet-like objects orbiting well beyond that of the Kuiper belt at the far reaches of the solar system. The Oort Cloud is thought to be the primary source for long period comets in the solar system. Both the Kuiper Belt and Oort Cloud are believed to be remnants from the formation of the solar system.