GoKawiilSome good news and some bad news. The good news is that, contrary to earlier fears, Earth will probably never be swallowed by the sun. The bad news, of course, is that none of us will be around to find out.
Scientists have long estimated that in about 5 billion years, the sun will run out of fuel, first expanding into a red giant and eventually becoming a white dwarf that will continue cooling for tens—if not hundreds—of billions of years. Amid this dramatic sequence of cosmic events, the fate of Earth remains uncertain.
Will it be pulled into the expanding red sun and disappear forever? Or, though long since rendered uninhabitable, will it continue orbiting the white dwarf remnant of the Sun until the universe reaches its eventual heat death?
Until now, the prevailing view among astrophysicists favored the first scenario. But a new study published in Astronomy & Astrophysics overturns that expectation, presenting new evidence that Earth may survive the sun's transformation into a red giant after all.
The Sun’s Life Cycle
To understand what lies ahead for the planets of the solar system, you need to look inside the sun itself. At present, the sun is in its main-sequence phase, a long period of stability that has lasted for about 4.5 billion years, during which it is powered primarily by the fusion of hydrogen into helium.
This phase will continue for billions of years, but the sun will gradually become hotter and more luminous. Eventually, it will grow bright enough to evaporate all of Earth's surface water, making our planet uninhabitable within the next two billion years.
About 5 billion years from now, the sun's long period of stability will come to an end. By then, the hydrogen in its core will have been exhausted. The helium core will contract under its own gravity, heating up and triggering hydrogen fusion in a surrounding shell. As a result, the sun's outer layers will expand enormously while its surface cools dramatically, giving it the characteristic red color of this stage in a star's evolution. And this is where the mystery surrounding Earth's fate begins.
A Complex Tug-of-War
The sun's enormous expansion will profoundly reshape Earth's orbit through the interplay of two opposing effects. On one hand, the sun will lose a significant amount of mass through powerful stellar winds. As its gravitational pull weakens, Earth's orbit will gradually drift outward. On the other hand, the planet's increasing proximity to the sun's extended gaseous envelope will produce drag, while tidal forces—the difference in gravitational pull exerted on the near and far sides of an object, which can gradually alter planetary orbits—will act as a brake on Earth's motion.
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