The mission is called MESSENGER, for Mercury Surface, Space ENvironment, GEochemistry and Ranging. On March 17 it will pull into orbit around mercury, after more than six years of maneuvering between the Earth, Venus and Mercury itself.
Mercury is the closest planet to the sun, completing one of its revolutions in only 88 days. Surface temperatures on during the day top out at 426 degrees Celsius (798 degrees Fahrenheit) — hot enough that lead and zinc would melt like ice on a hot day. Nighttime temperatures plunge to -173 degrees C (-279 F), cold enough to liquefy neon gas. Mercury also spins very slowly, and does so in such a way that a single day on Mercury lasts 176 days — two of the planet's years.