The solar system is about 4.6 million years old. It began as a spinning disc of hydrogen and helium which, over a period of 25 million years, formed into the sun and surrounding planets.
The Sun is a nuclear reactor generating energy by the conversion of hydrogen into helium. The rate of conversion is relatively slow, there is enough hydrogen for another 15 billion years.
The granular surface (photosphere) is constantly changing, the main features of which are sunspots and erupting jets of gas (spicules). Above the surface is a hydrogen chromosphere and beyond this is the corona. The Sun is classified as a G2 yellow dwarf.
The inner four planets all have an iron core, rock mantle and a crust of varying thickness.
So called because of their gaseous surfaces (albeit frozen), all the gas giants have ring systems of dust and ice fragments. In some cases the rings are 'shepherded' by small satellites.
1. The orbital (sidereal) period is measured in "Earth" units. For example:
1 Mercury year = 88 Earth days.
2. The masses of the planets are given relative to the mass of the Earth which is 6 × 1021 tonnes.