Yesterday the MESSENGER spacecraft circled behind Mercury one last time, where no one on Earth could see it, and slammed into the surface of the intemperate planet at an estimated 8750 miles per hour. It was the second probe to visit Mercury—Mariner 10 completed three fly-bys of the planet in 1974, and according to NASA, still orbits the sun; probably fried, out of fuel, a derelict.
MESSENGER began its scientific mission in 2011. With its destination so near to the sun, under the influence of immense gravitational force, MESSENGER had to fly by "Earth once, Venus twice, and Mercury itself three times" in order to slow down and gently insert itself into orbit. The spacecraft proceeded to take over 100,000 images of Mercury's surface, allowing NASA to map 100% of the innermost planet of our solar system. After completing its primary objectives in 2012, Messenger's mission was twice extended. According to Wikipedia, "MESSENGER's instruments have yielded significant data, including a characterization of Mercury's magnetic field and the discovery of water ice at the planet's north pole." Using an array of spectrometers and a laser altimeter, MESSENGER also revealed a ton of information about the geology and composition of the planet, including evidence of past volcanism and a liquid iron core.
MESSENGER continued its surveys until its dying breath. After running out of liquid propellant, its operations were extended four weeks with the innovative appropriation of gaseous helium as a fuel source. Finally, when there was nothing left in the tanks, MESSENGER made its very own, brand new crater on the planet to which its existence was dedicated.