MESSENGER, short for "Mercury Surface, Space Environment, Geochemistry and Ranging," has been in orbit around the planet since March 17. It took 364 images today, will take 1,185 photos over the next few days and wind up with over 75,000 images altogether over the next year.
Mercury is the planet closest to the sun. It's got a year of just under 88 days and an iron core that creates weak planetary magnetism. The temperature ranges from a brisk -364 degrees Fahrenheit at the poles to a cozy 800 degrees in the sun.
According to NASA:
"In the course of the one-year primary mission, the spacecraft's seven scientific instruments and radio science investigation will unravel the history and evolution of the Solar System's innermost planet."
And why visit? As one of the "terrestrial" (or rocky, as opposed to gaseous, planets), it can teach us about Earth, among other things.
"Understanding this 'end member' among the terrestrial planets is crucial to developing a better understanding of how the planets in our Solar System formed and evolved."
Also, because it's awesome. Being a part of the process of unveiling, of sharing, at however great a remove, the adventure of approaching, investigating and understanding another of our system's planet, that's awesome too.