Like many stars, the sun is naturally growing in size and brightness over time. Models suspect that the sun has grown 40% in its first 4.5 billion years of existence. If such models are correct, the sun is expected to continue to grow to be 10% brighter over the next 1 billion years. Scientists further predict that in 5.5 billion years the sun's core will run out of hydrogen fuel beginning its quick transformation into a red giant. At this point, the star will surely absorb Mercury and Venus, while Mars and further planets will most likely be pushed away. The fate of the Earth, however, is unknown.
The reason is that in the course of ballooning outward, the Sun will blow off a substantial share of its mass, says the author of the article. Thus, the Sun’s gravitational grip on its planets will be weakened, and they will retreat to more distant orbits. The Earth will wind up about where Mars is now, "on the border line between being engulfed or escaping engulfment," as Dr. Livio put it. Whether or not the Earth is engulfed depends on which of two effects wins out. At the same time that the Earth is retreating to a safer position, tidal forces between it and the expanding Sun will try to drag the planet inward and downward.
Read the article here to see what some scientists have determined to be Earth's inevitable fate after much research and calculations.
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