Questions of life

In 1961, astronomer Frank Drake drew up a list of questions to help calculate how many intelligent communicating civilisations live in our Milky Way Galaxy.

1. How many stars does our galaxy contain?
2. What fraction of stars have planets?
3. How many wet, warm planets occur in each planetary system?
4. If the planet is wet and warm, what is the chance of life breaking out?
5. What is the chance of life becoming intelligent?
6. What is the chance of this intelligent life being able to communicate with life elsewhere?
7. During what fraction of a planet's existence will intelligent communicating life exist?

In 1997, scientist Carl Sagan worked out that one million intelligent, communicating life forms exist in our galaxy and the nearest is only 300 light years away.