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How the Solar System Will End

Whatever direction life on Earth takes over the next few billion years there is one certainty. One day it will all end. Life may cease to exist on Earth before the end of the planet, there are many potential scenarios that could lead to this happening, but it is absolutely certain to end when the Sun reaches the end of its life cycle. Stars have a finite life cycle and in five and a half billion years our Sun is due to expand into a massive Red Giant, engulfing the Earth. However, whether humans are still around to see it remains debatable.

The fate of humanity realistically must be different to that of planet Earth. Given the enormous time scale until the expansion of the Sun it would seem reasonable to assume that our species would have moved on from our current form. If four billion years has been enough time for all of life on Earth to evolve to reach civilisation then by adding almost twice as much time again we'll be sure to see some drastic changes. A question is will the human race, or our descendents, remain until that time or will be have been long wiped-out?

The possible outbreak of World War Three and a nuclear apocalypse is a topic that has been widely spoken about and explored. The threat of nuclear war reached an all-time high during the Cold War and it is believed that the world stood on the brink during the Cuban missile crisis. Fortunately no bombs were launched and with the dissolution of the Soviet Union and increasing nuclear disarmament the threat of a nuclear annihilation seems to have passed.

Man's end may come from self-imposed means or any number of natural disasters. A large impact event could prove fatal to life, and large volcanic activity, cosmic ray bursts and even extra-terrestrial invasions have been discussed by scientists as possible ends. The validity of many of these concerns is variable and the fate of mankind is enough for an article in itself, what I would like to look at here is what will certainly happen, regardless of whether our species lives or not.

The Sun, the object that provides all the energy used by the Earth, will be the cause of its end. Stars go through complex life cycles, starting with their birth and eventual demise. Each star will last billions of years, and depending on its mass and elements can form into a number of different types. Currently the Sun is a main sequence star, generating energy through nuclear fusion of hydrogen into helium. The Sun will spend around 10 billion years as it is now before going on to the next stage of its life.

The Sun becomes brighter and larger as it grows older. In its first four and a half billion years it is estimated that the Sun has increased in brightness by around fourty percent. In one billion years time the Sun will have increased in brightness by around ten percent, boiling the oceans and scorching the surface. This in itself is enough to end life as we know it now. However in five and a half billion years the Sun will run out of hydrogen to burn in its core. It will start burning the hydrogen from the outer layers, shrinking the core and massively expanding the volume of the Sun, transforming it into a red giant.

Mercury and Venus will be swallowed by the growing star, while the fate of Earth is less immediately clear. If the Earth escapes being consumed by the growth of the Sun it will be burned to a charred, lifeless rock. After the red giant phase the Sun will continue to shed its outer layers into a planetary nebula until just the core remains. The core will cool into a white dwarf star and fade over billions of years. The Sun is not large enough to form a black hole or a supernova and it seems that the relatively inglorious end of forming a white dwarf is inevitable. The fate of Earth also seems to be certain and while not a concern for us living here at the moment, at some point in time it will be a very real problem, although quite what form life takes by that point remains to be seen.

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