<P> This is a relatively peaceful event, nothing akin to a supernova, which the Sun is too small to undergo as part of its evolution . Any observer present to witness this occurrence would see a massive increase in the speed of the solar wind, but not enough to destroy a planet completely . However, the star's loss of mass could send the orbits of the surviving planets into chaos, causing some to collide, others to be ejected from the Solar System, and still others to be torn apart by tidal interactions . Afterwards, all that will remain of the Sun is a white dwarf, an extraordinarily dense object, 54% its original mass but only the size of the Earth . Initially, this white dwarf may be 100 times as luminous as the Sun is now . It will consist entirely of degenerate carbon and oxygen, but will never reach temperatures hot enough to fuse these elements . Thus the white dwarf Sun will gradually cool, growing dimmer and dimmer . </P> <P> As the Sun dies, its gravitational pull on the orbiting bodies such as planets, comets and asteroids will weaken due to its mass loss . All remaining planets' orbits will expand; if Venus, Earth, and Mars still exist, their orbits will lie roughly at 1.4 AU (210,000,000 km), 1.9 AU (280,000,000 km), and 2.8 AU (420,000,000 km). They and the other remaining planets will become dark, frigid hulks, completely devoid of any form of life . They will continue to orbit their star, their speed slowed due to their increased distance from the Sun and the Sun's reduced gravity . Two billion years later, when the Sun has cooled to the 6000--8000K range, the carbon and oxygen in the Sun's core will freeze, with over 90% of its remaining mass assuming a crystalline structure . Eventually, after billions more years, the Sun will finally cease to shine altogether, becoming a black dwarf . </P> <P> The Solar System travels alone through the Milky Way in a circular orbit approximately 30,000 light years from the Galactic Centre . Its speed is about 220 km / s . The period required for the Solar System to complete one revolution around the Galactic Centre, the galactic year, is in the range of 220--250 million years . Since its formation, the Solar System has completed at least 20 such revolutions . </P> <P> Various scientists have speculated that the Solar System's path through the galaxy is a factor in the periodicity of mass extinctions observed in the Earth's fossil record . One hypothesis supposes that vertical oscillations made by the Sun as it orbits the Galactic Centre cause it to regularly pass through the galactic plane . When the Sun's orbit takes it outside the galactic disc, the influence of the galactic tide is weaker; as it re-enters the galactic disc, as it does every 20--25 million years, it comes under the influence of the far stronger "disc tides", which, according to mathematical models, increase the flux of Oort cloud comets into the Solar System by a factor of 4, leading to a massive increase in the likelihood of a devastating impact . </P>

The moon probably formed at the same time that earth formed