~ Mercury is a small, rocky planet.
   
~ Mercury has been visited by the Mariner 10 spacecraft. Mariner 10 has mapped a little less than half (45%) of Mercury's surface.
   
~ Scientists think that there may be *volcanic activity* on Mercury. They are still studying information sent to Earth from the Mariner spacecraft to make sure.
   
~ The temperature on Mercury ranges from 90 K to 700 K.
   
~ It was once believed that there was no water on Mercury, but this turned out to be false. Recent radar information shows evidence of ice at Mercury's north pole! The ice hasn't melted because it is protected from the Sun's heat by shadows of some craters.
   
~ Unlike many of our nine planets, Mercury has no moons.