Mercury is the smallest planet. It has no moon and looks a lot like one.

01 Mercury_transit_1.jpg
This is Mercury. No not the big yellow ball or even the little black smudge on the left. Mercury is that little dot in the middle. This is a picture of it crossing the sun in 2006.
02 Mercury_Globe-MESSENGER_mosaic_centered_at_0degN-0degE.jpg
Many many objects in space have crashed into it over the years leaving it heavily cratered just like the Moon.
03 Mercury Meesnger Caloris Basis.jpg
This is the Caloris Basin – one of the largest impact craters in the solar system. It is surrounded by mountains two kilometers high.
04 Colors_of_the_Innermost_Planet.jpg
The colours in this picture, from 2008 when we flew a space probe there, were enhanced to show the different stuff (chemicals and minerals) that make up the planet.
Mercury_in_color_-_Prockter07-edit1 MESSENGER 2008.jpg
Because it’s the closest planet to the sun we often think of it as small burning ball – but here it looks like a calm moon.