Flexi Says: If Earth was the same size as the Sun in diameter and volume but with Earth's usual mass, then Earth's surface would be very far away from its center. The force of gravity at Earth's surface would therefore be very weak compared to its current value. The gases that make up the atmosphere would float away in the low gravity environment. Life as we know it could not exist. Now, if both the size and mass of Earth were the same as that of the Sun, then Earth would have become another star. It would collapse under its own mass due to gravity, and fusion would begin in the center, forming a new star.