NASA’s Messenger spacecraft will make history tonight when it becomes the first probe to orbit the planet Mercury. Since it launched in August 2004, the orbiter has made nearly 15 laps around the sun, flying by Earth, Venus and Mercury to slingshot itself into just the right position for orbital entry. Starting at 6pm tonight the Messenger spacecraft will fire its main thruster for about 15 minutes in what scientists call an “orbital insertion burn.” If all goes well, the maneuver should slow the probe down enough for it to be caught by Mercury’s gravity and enter orbit. In the mid-1970’s NASA flew spacecraft quickly past Mercury which gave us just a peek at what the planet nearest to the sun looks like. Because Messenger is orbiting the planet it will be able to hang around for months if not years and take thousands of pictures and measurements.