As part of the ESA project „CAVES 2012“, our group is investigating how the presence of humans changes the natural microbiological community in a cave. In September 2012, a team of six astronauts will spend six days in a cave. We would like to determine the impact and how much influence the presence of human has on the microbiological community and how many foreign contaminations they will generate. Due to the cave’s isolation and harsh climate it is comparable to other planets. In this respect we hope to gain valuable insights for questions regarding planetary protection.