In 2011 the Messenger spacecraft will be the first to enter into orbit around Mercury. While it performs its flyby maneuvers prior to establishing orbit, photos are being sent back revealing a thoroughly cratered surface. In this photo, taken on October 6, 2008, half of the 120-mile wide crater Stravinsky is seen pressing against the lower, wider, rougher-edged crater Vyasa. Click for a larger view with captions.

About 40% the size of Earth, Mercury is the densest of the 8 planets, made of nearly 2/3 metal (iron and nickel) in a large core. Its close proximity to the Sun gives it a daytime temperature of 800º F, but without much of an atmosphere to hold that heat its nighttime side cools to -300º. And its nights are both cold and long…Mercury rotates much slower than Earth, so one “day” takes 4,224 hours to complete – 176 Earth days between one sunrise to the next.

(And you thought your work week lasted forever.)

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington