From the Radio Times:

A keynote lecture delivered before an audience at BBC Radio 3's Free Thinking festival of ideas. Professor John Zarnecki asks "Space: Why are we there?" and draws on over 30 years of involvement in space missions to attempt an answer

Sorry about the very short notice (Radio 3 is an unusual place for this to turn up and I only just noticed that distinctive Z name buried in the small print a few minutes ago).

But if you miss it it should be available on BBC Radio's 'listen again' service for the next week or so.