Our sun is about half way through its life cycle. It formed from a big cloud of gas and dust, became a star when its center began the fusion of hydrogen into helium, and reached the stable phase it is in now. Eventually, our sun will expand its outer shell and become a red giant star. Then it will shrink into a small, white dwarf star and eventually fade into a black dwarf star. What will happen to the Earth when the sun goes through all of these changes in the future?

The first effect of the aging sun has already begun. As the sun changes hydrogen into helium at its core, the core slowly shrinks, fusion speeds up, more energy is released, and the sun increases its brightness. The sun is 30% brighter now than when it formed 4.6 billion years ago. As the sun heats up, Earth’s atmosphere heats up too. The surface rocks weather faster and carbon dioxide decreases. The plants need carbon dioxide to live. Plants make oxygen for people and animals to live. All life suffers and gradually decreases.

The next problem is the atmosphere. The sun’s increased heat also heats our atmosphere. The worst effect of atmospheric heating is the increase of water vapor in the air. The polar caps melt completely, the oceans warm up and begin to evaporate on a vast scale. The water vapor greatly increases and traps heat in the atmosphere.

Sunlight in the upper atmosphere breaks down water molecules into oxygen and hydrogen. The lightweight hydrogen toms are fast-moving and escape into space. The more water vapor in the air the faster the breakdown happens. Eventually, Earth loses its water and becomes bone-dry, very much like Venus is now. The carbon dioxide from the ocean enters the atmosphere, trapping heat and causing more greenhouse effect heating. The very high temperatures soften Earth’s crust and accelerate volcanic activity. Volcanic activity releases more carbon dioxide into the atmosphere from inside the Earth. As a result, Earth has no water, and is enclosed in a thick carbon dioxide blanket (similar to Venus). Earth has lost its biosphere and no life can survive on Earth any longer.

After Earth becomes unlivable, the sun’s outer shell expands as the outer layers puff out. The sun’s outer layers expand to 2 or 3 times their current size and the sun becomes a subgiant star. When the hydrogen in the core is totally exhausted, the sun’s surface layers expand to 160 times its current size. The sun becomes a red giant star. The sun engulfs and vaporizes Mercury, then Venus.

For Earth, there are two possible endings. Some scientists believe the solar wind may blow Earth into an orbit near Mars, saving it from being incinerated in the expanding sun. If that happens, Earth’s surface temperature would exceed 1,500 C (2,700 F). Earth would be a molten ball of lava with its entire atmosphere and probably its former crust boiled away into space. The other option is equally grim. Other scientists believe that Earth is pulled into the quickly expanding edge of the sun. The Earth is incinerated and its ashes are scattered in the final solar winds.