Mercury

Mercury is a planet, the smallest in our Solar System and the closest to the sun. Its semi major axis is 58 million km from the sun.(A semi major axis is the average distance in its elliptical orbit.) Its diameter is 4879 km. The average temperature is above the boiling point of water at 130 degrees Celsius. It has high concentrations of volatile elements and astronomers are not sure why. ( The elements will boil away due to the heat.) A day is 58 Earth days and 16 hours and a year is 88 Earth days.