One solar day on a planet is the length of time from noon to
noon. A solar day lasts 24 hours on planet Earth. On Mercury a
solar day is about 176 Earth days long. And during its first
Mercury solar day the MESSENGER spacecraft has imaged nearly the
entire surface of the to generate a global monochrome map at 250
meters per pixel resolution and a 1 kilometer per pixel
resolution color map. Examples of the maps, mosaics constructed
from thousands of images made under uniform lighting conditions,
are shown (monochrome at left), both centered along the planet's
75 degrees East longitude The MESSENGER spacecraft's second
Mercury solar day will likely include more high resolution of
the planet's surface features. (Editor's note: Due to Mercury's
3:2 spin-orbit resonance, a Mercury solar day is 2 Mercury years
long.)