If the Sun were smaller than Earth, our Solar System would undergo a complete transformation, and life on Earth would be vastly different from what it is today.
It would take 1.3 million Earths to fill the volume of the Sun. The Sun is so large that it accounts for 99% of the mass of the entire system.
From Earth, the Sun appears very small because it is 150 million kilometers away from us. Suppose the Sun were smaller than Earth; Earth would become an uninhabitable place, and the Sun might cease to be a star.
In the universe, size is crucial, and distance is equally important. Earth is situated at just the right distance from the Sun to avoid freezing like Mars. It is also far enough away to prevent overheating like Venus.
We are fortunate to be in a habitable zone around the Sun. This means that the size of our planet, the size of the Sun, and the distance between them are the conditions that allow life to evolve on Earth.
What would happen if the Sun were smaller than our Earth?
Regardless of the scenario, life on Earth would be destroyed.
The mass of a star determines its color and temperature. Larger stars are hotter and blue, while smaller stars are cooler and red.
The Sun is a white star, not as large as a supergiant and not as small as a red dwarf. You might think that if the Sun were smaller, it would turn into a red dwarf with a smaller habitable zone. But that is not the case.
By definition, a star, whether a supergiant or a red dwarf, is a star only when it has nuclear fusion occurring in its core. How small can a star be? Currently, we have not measured many red dwarfs, but the smallest star we have discovered has a mass equivalent to 10 Earths. This level is close to the theoretical size needed for a star to sustain fusion. If it is smaller than 10 Earths, it is no longer a star but merely a cold and dark stellar remnant.
If, for any reason, the Sun were to shrink to a size smaller than Earth, this smaller Sun would lack the mass to generate fusion and would eventually burn out completely. Our Solar System would lose its only star.
Since the Sun is the gravitational source that keeps the planets in orbit, every planet, including Earth, would drift off into space in search of another anchor. Life on Earth would not end well.
Let’s assume again. This time, let Earth be larger than the Sun, while the size of the Sun remains unchanged.
The mass of Earth would be at least 333,000 times greater than it is now. Such a large planet would generate enough heat and pressure in its core to become a star itself. Of course, life would not be able to exist on this scorching star, but there is an interesting twist. Our star system would not have just one, but two Suns. It would become a binary star system, with two stars orbiting each other and planets orbiting around both.
Regardless of the scenario, life on Earth would be destroyed. However, life could evolve on other planets or even on the Moon.
The Sun plays a crucial role in the formation of planets.
About one-third of the star systems we find are binary or multiple star systems. Some of these have stable habitable zones. If we lived in a binary star system, the scenery would resemble Tatooine from the Star Wars series, with two Suns shining in the sky. This would be a magnificent sight and open up new possibilities for exploring extraterrestrial life.
In both scenarios, whether the Sun is smaller than the current Earth or the Earth is larger than the current Sun, life as we know it would be impossible. However, this highlights the importance of size and distance in maintaining life on planets. The current structure of the Solar System, with the Sun at the center and the planets orbiting around it, is the result of billions of years of evolution and delicate balance. This shows that in this vast and complex universe, even the smallest factors can determine the existence of life.
