<P> The Solar System will remain roughly as we know it today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5 billion years from now . This will mark the end of the Sun's main - sequence life . At this time, the core of the Sun will collapse, and the energy output will be much greater than at present . The outer layers of the Sun will expand to roughly 260 times its current diameter, and the Sun will become a red giant . Because of its vastly increased surface area, the surface of the Sun will be considerably cooler (2,600 K at its coolest) than it is on the main sequence . The expanding Sun is expected to vaporize Mercury and render Earth uninhabitable . Eventually, the core will be hot enough for helium fusion; the Sun will burn helium for a fraction of the time it burned hydrogen in the core . The Sun is not massive enough to commence the fusion of heavier elements, and nuclear reactions in the core will dwindle . Its outer layers will move away into space, leaving a white dwarf, an extraordinarily dense object, half the original mass of the Sun but only the size of Earth . The ejected outer layers will form what is known as a planetary nebula, returning some of the material that formed the Sun--but now enriched with heavier elements like carbon--to the interstellar medium . </P> <P> The Sun is the Solar System's star and by far its most massive component . Its large mass (332,900 Earth masses) produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium, making it a main - sequence star . This releases an enormous amount of energy, mostly radiated into space as electromagnetic radiation peaking in visible light . </P> <P> The Sun is a G2 - type main - sequence star . Hotter main - sequence stars are more luminous . The Sun's temperature is intermediate between that of the hottest stars and that of the coolest stars . Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, make up 85% of the stars in the Milky Way . </P> <P> The Sun is a population I star; it has a higher abundance of elements heavier than hydrogen and helium ("metals" in astronomical parlance) than the older population II stars . Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the Universe could be enriched with these atoms . The oldest stars contain few metals, whereas stars born later have more . This high metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets form from the accretion of "metals". </P>

9 planets of the solar system and their meanings