Dieses Portal bietet Basiswissen zum Thema Astronomie und zeigt aktuelle Forschungsarbeiten und -kooperationen in der Schweiz auf.

Image: ESO

Planets

Images taken by the Hubble Space Telescope in 2021 (from left to right): Jupiter, Saturn, Uranus and Neptune. The planets are not shown to scale.
Image: NASA, ESA, A. Simon, M.H. Wong and the OPAL team

A planet is a celestial body with a sufficiently large mass that, through the action of its own gravitational field, known as its gravity, is pressed into the most compact possible shape: a sphere. A planet also orbits the Sun or another star and is the sole dominant celestial object in its orbit.

A total of eight planets orbit our Sun. From the inside outwards, they are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto was considered the ninth planet until 2006, but was then downgraded to a dwarf planet. Planets also exist outside our Solar System, and these are known as exoplanets.

The inner four planets, Mercury, Venus, Earth and Mars, are terrestrial planets (or rocky planets). They are made of solid, rocky material, and their gaseous atmospheres contribute little to the total mass of each planet. Jupiter, Saturn, Uranus and Neptune, on the other hand, are mostly gaseous and probably have a small solid core. Because of their size, these are also known as gas giants.

Each of these planets embodies its own fascinating world which, in the case of Earth, we can explore on foot and, in the case of other planets, with space probes.