In our solar system we are lucky enough to inhabit the planet in the perfect spot. Out of our planetary neighbors, no other is close enough or far away enough from the sun to be able to harbor life as we know it. The sun is absolutely essential to our life and to the lives of nearly every other organism on the planet. If we were set closer to the sun or farther away, none of what we know today would exist. The Earth would either be frozen or overheated by being too far away or too close respectively. As it happened the Earth stakes claim to the sweet spot in the solar system. We ride along our 365 day, 5 hour and 48 minute long orbit each year, 93 million miles away from the sun, enjoying our spot and soaking in all it can give us.
The sun provides us with more than just light. It heats the Earth and allows essential life processes to occur. The sun produces energy by converting hydrogen into helium by way of a three stage process. In this process, two hydrogen atoms combine to form deuterium. This is called nuclear fusion. The deuterium atom then joins with another hydrogen atom to give us helium-3. Finally, two helium-3 atoms join to yield normal helium. At each level in this process, huge amounts of energy are released. This process occurs countless times in the core of the sun and gives us heat, radiation and light.
To produce the life supporting energy that we all depend on, the sun and other stars, have to burn fuel. That fuel is hydrogen and helium. The huge mass of stars produces massive gravity. This gravity threatens to collapse the star into a white dwarf. The energy the star produces counteracts this gravity, keeping the star a constant size. After a few billion years, a star can begin to use up all it’s fuel. At this point one of three things can occur depending on the size of the star. For stars near the same mass as our sun they will expand into a red giant. They will continue to cool as they become nebulae and eventually a white dwarf and black dwarf. Stars more massive will expand into a red super giant. Then they will explode in a brilliant burst in a supernova event. Then from there they will become either a neutron star or black hole. Our sun is not massive enough to become a black hole but its days are numbered just the same.
Our sun has been burning for about 5 billion years. It has about another 5 billion years left on its life span. When the sun’s fuel begins to burn out, it will expand into a red giant. At this point the sun will expand to 100 times its current size, easily swallowing the Earth. It will then begin to collapse back on itself and take on the form of a white dwarf. Our massive sun will be reduced to a glowing body about the current size of the Earth. As it cools more it will become an extinct black dwarf.
Every star goes through a similar cycle. The death of our sun is quite far off. If humans are around at that point, it’s doubtful that anyone or anything will survive. However, it seems more likely that whatever is on the Earth in 5 billion years will not be human at all. In the life cycle of the Earth, humans only account for a very small fraction of the life forms that have at one time or currently inhabit the Earth. Humans have only been around for a tiny amount of time in the Earth’s history. Whatever, if anything, is on Earth at the time of the suns demise will be post human. Those life forms will not be anything like the life forms we see today or are able to imagine. Perhaps that race of life forms will be able to adapt or move from Earth to somewhere warm.
There is a limit on the habitability of our solar system. The sun will expire and the clock is running. Our exploration of space and development of technology should continue to save future Earth inhabitants.