Mercury is the closest planet to the Sun and the eighth
largest. Mercury is
smaller in diameter than Ganymede and Titan but more
massive.
orbit:
57,910,000 km (0.38 AU) from Sun
diameter:
4,880 km
mass:
3.30e23 kg
Mercury has been visited by only one spacecraft, Mariner 10. It flew by three times in 1974 and 1975. Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST).