This week it was revealed that astronomers are about to start the most intensive ever search for alien life. The Breakthrough Listen project will scan stars in 100 galaxies for radio and optical signatures that indicate someone, or something, is out there.

Until now, the search for extraterrestrial intelligence - or SETI - has been met with an eerie silence. What makes scientists so convinced it's worthwhile looking for alien life?

What are the chances that we'll find it? And should we consider beaming our own messages out into the cosmos?

Joining Hannah Devlin are astronomer Frank Drake; Professor Geoff Marcy and Dr Andrew Siemion, both from the University of California, Berkeley; and Dr Nick Lane, an evolutionary biochemist at University College London, whose work looks at how life started on Earth.

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