Seeing the Solar System's future

Recent observations offer clues about whether the planets will survive our Sun's far-off fate of swelling out into the Solar System as a red giant. Colin Stuart investigates

- Colin Stuart

AIl good things must come to an end, even stars. Eventually, all-stars - including the Sun - will die and the Universe will fade to black forever. For now, our star is able to persist by constantly churning hydrogen into helium. This process, called nuclear fusion, creates enough outwards pressure to resist the relentless force of gravity trying to collapse the Sun into oblivion.

Currently, the Sun is getting through 600 million tonnes of hydrogen every single second and there will come a time when there is no hydrogen left to burn. Despite its voracious appetite for this abundant element, astronomers estimate that the Sun has about 5 billion years' worth of fuel left. Once the hydrogen is exhausted, gravity will win and the Sun's core will begin to collapse. With solar material now considerably more compressed, the temperature in the core will climb to a staggering 100 million degrees. That compares to the 15 million degrees you'll currently find in there. Meanwhile, the pressure will reach over a trillion times the atmospheric pressure here on Earth.

Such crazy temperatures and pressures mean that helium becomes the ingredient rather than the product, and it gets pressed into carbon and oxygen. The Sun will get through the equivalent of 10 Earth masses of helium every second. This 'helium burning' happens at a much faster rate than the previous slow-and-steady hydrogen-burning phase. The delicate balance within the Sun is now upset the other way. The outwards pressure is so great that it trumps gravity and the Sun begins to bloat into a red giant. It will eventually swell to swallow Mercury and Venus, and it may engulf Earth as well.