The smallest planet in our solar system and nearest to the Sun, Mercury is only slightly larger than Earth's Moon.From the surface of Mercury, the Sun would appear more than three times as large as it does when viewed from Earth, and the sunlight would be as much as seven times brighter. Despite its proximity to the Sun, Mercury is not the hottest planet in our solar system – that title belongs to nearby Venus, thanks to its dense atmosphere.. It is named after the Roma n god Mercurius (Mercury), god of commerce. Its orbital ec centricity is the largest of all known planets in the Sola r System.Mercury appears to have a solid silicate crust and mantle overlying a solid, iron sulfide outer core layer