SMART-1 launched in 2003 and was the first European spacecraft to go to the moon. It was also the first mission of a program called Small Missions for Advanced Research in Technology, which was a series of low-cost spacecraft that the European Space Agency launched to test new spaceflight technologies. SMART-1's primary objective was to test something called Solar Electric Primary Propulsion, or a solar-powered electric engine.
While it orbited the moon for almost two years, it looked for water ice and other chemicals on the lunar surface. When it slammed into the moon, that was also done for science. Astronomers back on Earth watched the impact with their telescopes, hoping that it would give them some insight into the mechanics of meteor impacts.
Source: space.com