I have been waiting a LONG time for this! MESSENGER was launched in August of 2004 and had its 3.5 year journey to Mercury, the most mysterious of our inner planets! And here, the first unveiling of the unseen side of our first planet! I love it.
Mercury was suspected in the third millenium BC and then studied by Galileo (my hero) in the 17th century. Scientists since then have tried to study it but its proximity to the sun has always made this problematic. In the 1800s they came up with another planet, Vulcan, to explain the erratic behaviour of Mercury's orbit. Vulcan was later found to not exist.
The most fascinating thing about Mercury is its orbit. It circles the sun every 88 days and its solar day is 176 of our days... Wow. Its sidereal day is 58.7 of our days. And yet, Saturn, a huge planet compared to tiny fleet-footed Mercury, has a sidereal day of 10.5 Earth hours. Go figure!