Portal:Astronomy/Picture/Week 40 2006

Mercury is a rather poorly studied planet. It has only been visited by one spacecraft, Mariner 10 in 1974 and 1975, and only half its surface has been mapped in detail. It rotates about its axis exactly 1.5 times in each orbit around the Sun, making Mercury the only planet with an orbital resonance in the solar system with a value other than 1:1.