Mercury is the closest planet to the Sun due to its position and forming process within our solar system. When the solar system was forming about 4.6 billion years ago, dust and gas began to coalesce under gravity, creating the Sun and the planets. The inner planets, including Mercury, Venus, Earth, and Mars, formed from materials that could withstand higher temperatures. Being the closest to the Sun, Mercury had to deal with intense heat and radiation, which influenced its composition and size.
Another key factor is that Mercury’s orbit is tightly bound to the Sun due to the latter’s massive gravitational pull. The gravity of the Sun pulls Mercury into a rapid orbit, making it travel around the Sun in just 88 Earth days. This shorter orbital period is a direct consequence of being in closer proximity to the Sun, where the gravitational force is stronger.
In a broader sense, each planet’s distance from the Sun is a result of various factors, including the initial conditions of the solar nebula, gravitational interactions, and their own formation processes. So, Mercury’s closeness to the Sun can be attributed to a combination of its formation, gravitational dynamics, and the environmental conditions present in the early solar system.