A SpaceX rocket stage launched in February 2015 is on course to smash into the Moon on March 4. Weighing about 4 metric tons, the hulking steel tube will hit the moon at about 2.58 km/second (around 5,500 miles per hour.) Unfortunately it's expected to hit on the far side of the Moon so we won't see the collision from Earth. From Ars Technica:
This information is important because it will allow satellites presently orbiting the Moon, including NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan-2 spacecraft, to collect observations about the impact crater. With the LCROSS mission, NASA deliberately impacted a spent rocket upper stage into the Moon in 2009 for this purpose. Although scientists are most keen to understand the presence of ice at the lunar poles, being able to observe the subsurface material ejected by the Falcon 9 rocket's strike could still provide some valuable data[…]
It's likely that this will be the first time a piece of space hardware unintentionally strikes the Moon.
More data here from Project Pluto.
top image: SpaceX