ABSTRACT
Thirty million years is the time it would take for the Sun to return to a stable state if the rate of energy generation in its core were suddenly to be changed. In other words, the rate of solar energy production at the core of the Sun is surprisingly stable with respect to our own timescale.2 That situation is slowly evolving though, as the hydrogen content of the Sun’s core is gradually transformed into helium, forcing the nuclear furnace to start a slow upward journey from the bottom to the surface looking for more hydrogen to burn. Consequently, the temperature of the upper layers of the Sun’s interior increases with time and solar luminosity becomes brighter and brighter. This process explains why just after the onset of fusion, our young Sun was about 30% fainter than at present. Since that time, its brightness has increased by 1% every 100 million years, making all planets and bodies of the Solar System warmer and warmer, including our own. After another five to six billion years, when all the hydrogen content in the center of the Sun is exhausted, our Sun will become a red giant, several hundred times its initial diameter, from then on living on helium fusion in the center and hydrogen burning in a surrounding shell. This will last for a few hundred million years until it sheds about one quarter of its original mass into the Milky Way. The rest will condense within a few thousand years into a brilliantly shining, extremely hot body the size of Jupiter, which will ionize the previously expelled mass and turn it into a glowing shell, one of the most beautiful objects of the deep sky, a planetary nebula. Eventually and very slowly, within 10 billion years, the brilliant former stellar core will cool down to a dim white dwarf as pale as light from the full Moon. Long before that ultimate catastrophe, approximately one billion years from now, with a Sun 10% brighter than at present, the Earth will have been transformed into a Venus-type planet, with the Sun’s transformations boiling off our oceans and transforming our home planet into an unlivable scorching dead body. A fatal future that most probably will happen long after all life has disappeared from our earthly living quarters!
