Monday, February 24, 2025

How does the Earth avoid being swallowed by the red giant Sun?

On average, the distance between Earth and the sun is slowly increasing because the sun is losing mass. As the thermonuclear fusion reactions continue inside the Sun, there is a decrease in the Sun's mass. The continued, steady loss of mass of the Sun over millions of years results in a reduced gravitational pull of the Sun and so an expansion of the orbits of the planets.

As a red giant, our Sun will expand and heat up, forcing its current habitable zone, which now encompasses Earth, outward. Credit; Astronomy: Roen Kelly

Over the course of the sun's remaining lifetime — i.e., another 5 billion years or so – it is estimated that the sun will lose about 0.1% of its total mass when it reaches the red giant stage. 0.1% doesn’t sound like much, but it is a helluva lot of mass – equivalent to Jupiter’s mass. When the sun loses mass, its pull on Earth weakens, leading it drift away from the Sun about 6 centimeters per year.

It is estimated that the Sun-Earth distance may increase to about 150% of what it is now.