The Sun is the central star of our solar system and all other planets, moons, asteroids, comets and satellites revolve around it.
The planets can be divided into two categories: terrestrial (rocky) and jovian (gaseous). Earth, Mercury, Venus, Mars and Jupiter are terrestrial planets; Saturn, Uranus and Neptune are jovian planets.
Sun
The Sun is the heart of our solar system, where most of the physical processes take place. It’s the main source of heat and light that allows life on Earth, and it’s also responsible for ejecting vast quantities of interplanetary dust and gas, known as the solar wind, into space.
The star was formed around 4.5 billion years ago from a molecular cloud that was originally mostly hydrogen gas, which later melted into helium through nuclear fusion. Some of that material cooled and formed planets, asteroids, and comets in our solar system.
NASA has many space missions observing the Sun, such as the Parker Solar Probe, to learn more about its composition and how it works. It has also used its observations to make better predictions about space weather and how it affects Earth. For example, its data have helped predict seven out of nine major solar flares that occurred during the last solar cycle.
Planets
There are eight planets in our Solar System. These include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
These planets have almost circular orbits that lie in an ecliptic plane (an oval-shaped path around the Sun). In addition to these planets, there are also moons.
Our Earth is the largest rocky planet in the Solar System. Its surface is shaped by a mosaic of mobile plates that recycle volatiles and regulate its temperature.
The outer planets — Jupiter, Saturn, Uranus and Neptune — are gas giants that are much larger than our Earth. They are primarily made of hydrogen and helium, although some astronomers believe they might have solid cores. The vast Kuiper belt contains thousands of icy bodies. Some of these are thought to have originated from the ices that accreted to the cores of Neptune and Uranus.
Moons
All but two of our Solar System’s planets are accompanied by a retinue of moons, some of them orbiting the planet and others orbiting small objects in the system.
They can range from large irregular objects to small, dense rocky worlds with atmospheres or oceans beneath their surfaces. Some of these worlds are also home to volcanoes and craters.
The largest among them are Jupiter’s moon Io, which has hundreds of volcanoes, and Saturn’s Titan, which has a thick atmosphere. But among the smaller moons, there are many interesting things to see and learn about.
For example, scientists have discovered that the surface of the Moon releases water when it is bombarded by micrometeoroids. This suggests that the moon formed from a combination of small meteorites and asteroids leftover in the Solar System after the formation of the planets.
Asteroids
Asteroids are rocky bodies that were left over from the early formation of the solar system. They likely formed from the protoplanetary disk that surrounded the Sun but never had enough mass to form into the roughly spherical shape required to be called a planet.
They are found in the asteroid belt, a region of space between the orbits of Mars and Jupiter. This vast belt, which is a few times as far from the Sun as Earth is, contains between one and two million larger than 1 km in diameter asteroids and millions of smaller ones.
Many asteroids in the main asteroid belt are grouped into ‘families’, which show similar orbits and spectral features in their light. These asteroid families are important because they help scientists understand how asteroids formed and evolved through time.
Satellites
Earth, the moon, and planets like Venus and Saturn are examples of natural satellites. Thousands of artificial satellites orbit Earth, and some take pictures that help scientists learn about the sun, other planets, dark matter, and faraway galaxies.
Unlike natural satellites, most man-made or artificial satellites are tasked with providing useful services to humankind. These services include broadcasting, telecommunications, and data communications.
Satellites come in all shapes and sizes, but they all have two parts in common – an antenna that sends information to Earth ground and a power source. This may be a battery or solar panel that makes power by turning sunlight into electricity.