Mercury is the closest planet to the sun.  It is 57,910,000 km away from the sun, making it the second hottest planet in our Solar System.  For Mercury to orbit the sun once, it takes only 88 Earth days.  It has a diameter of 4,880 km and a mass of 3.30e23 kg. It is the second smallest planet in our Solar System.  The land mass of Mercury is mainly dry, barren, and lumpy.