Mercury. Mercury is the only elemental metal that is liquid at room temperature. One of five planets visible with the naked eye a, mercury is just 4,879 kilometres across its equator, compared with 12,742 kilometres for the earth.
Mercury is a scarred world covered in craters, ridges, and bright debris from numerous impacts. Mercury’s proximity to the sun has also been exploited to confirm predictions made by relativity theory about the way gravity affects space and time.