What has the space satellite 'Mir' discovered

Also why was it launched?

Mir was a Russian-built space station, and was the first multi-module space stations in use. It was originally going to be occupied for 5 years, but the mission stretched to 11. The US and Russia came to an agreement, and the Russians allowed the US Shuttle to doc, and to have astronauts stay on Mir for the last few years of it's service, to gain in-space experience.
The record setting stay goes to a Russian Cosmonaut, Valeri Polyakov, launched in January, 1994, and stayed at Mir for 437 days.