We are used to the fact that the single celestial body in the Solar System is considered to be the only star - the Sun. But let's imagine that this fiery sphere of gas and plasma will lose the title of the largest object? What then happens to the Earth, other planets and the whole system?
It is important to understand that the sun is really huge! If we reduce our star to the parameters of a basketball, the Earth will become the size of a sesame seed. It will take 1.3 million planets to fill the solar volume. The sun is so massive that it takes 99% of the mass of the solar system.
But let's consider a scenario in which the Sun is smaller than the Earth. In this case, the entire solar system would change. The bad news is that the Earth will become uninhabitable, and the Sun ... well, it will cease to be a star.
Comparative size of the moon and earth
If we are talking about the universe, then size does matter. The same goes for distance. The Earth was lucky, because it is in the habitable zone, so it did not burn like Venus and did not stop, like Mars. The star mass determines the color and temperature of an object. Large stars are more hot and blue, and small stars are cold and red. You might think that reducing the solar size will make him a red dwarf. But there is a certain limit when a star remains a star (reactions take place in its core).
It is believed that the smallest star supporting nuclear fusion does not fall below the border of 0.075 solar masses. If our Sun had become less than this mark, then it would have no mass left to support nuclear fusion.
Comparative dimensions of 2MASS J0523-1403 - one of the smallest stars in the universe
In fact, the solar system in this scenario is losing a star. Since the Sun is a source of gravity, keeping us in orbit, all the planets would have strayed off course and traveled to outer space in search of another gravitational anchor. For earthlings this is not the best option, because we easily crash into another planet or die from cold in darkness.
Let's fantasize and look at the situation differently. What if the Sun remains the same size, but the Earth will become larger (surpasses the Sun)? In this case, the Earth’s mass will increase 333,000 times, and the gravity index will increase with this. People would die immediately, because such a gravitational indicator simply breaks our bones. In addition, the planet will begin to generate much more heat and pressure in the core, which will allow it to become a star.
It turns out that all life on Earth will die out, and the planet itself will turn into a star. Then the Solar system will consist of two stars orbiting around each other, and the planets will change their orbit (although during the Earth transformation Mercury, Venus and Mars may die).
In any case, life on Earth will disappear, but will be able to appear on other planets and will enjoy the sunrise and sunset of the two suns. But it is better to leave everything as it is, because both hypothetical scenarios lead to our death.