Lord Rees said he believed that astro-physicists could be able to view images of distant planets outside the solar system as soon as 2025. This could potentially lead to the discovery of some form of life on them.
When asked what changes could be expected in science in the next 40 years, he said understanding more about the "origin of life, the place where it exists, and whether aliens exist, is going to be crucial", the Daily Mail reported.
The astronomer was speaking at the launch of Professor Stephen Hawking's new series Grand Design, due to begin next Thursday on the Discovery Channel.
Lord Rees, who has been Astronomer Royal - a senior position within the Royal Household offering advice to the Queen on astronomical matters - since 1995, said: "Within 10 or 20 years we will be able to image other planets like the earth, orbiting other stars.