Dr. Gerard van Belle
Dr. Gerard van Belle Astronomer, Lowell Observatory
Well, at the end of the sun's life, the sun will start to run out of nuclear fuel at its center. It'll have taken all the hydrogen that's at its core, and due to the extreme temperature and pressure there, have fused that into helium. The problem is that the helium, if you want to use that as a nuclear fuel, you need more pressure and more temperature, which isn't present, at least in the sun as it currently is. What'll happen is the core will contract, and as the core starts to get smaller and smaller, it actually causes a shell around the core to burn even more, with more alacrity, and swell the sun up. It becomes a red giant.
The inner planets, such as Mercury and Venus, will probably be swallowed up by the sun. Earth will probably also be swallowed up, though there are some people that think that as the sun swells up it'll start to lose mass and basically will shed material away from it. And so the Earth may either fall into the sun as it swells, or basically just drift off into space as the sun's gravity becomes less and less strong and less and less able to keep the planets in place. Either way, it's not a good outcome.
Is our sun unique?
Answered by Dr. Gerard van Belle, Science Channel and 1 others
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