Mike Holcombe from Largs in Scotland asks, "How do we look for alien life and what are we expecting to find?"
In the first of two episodes on the search for ET, Hannah and Adam look for life inside the Solar System. How do we define life and why we obsessed with finding it on Mars? Or should we be looking for space squid on Europa instead?
Features interviews with planetary scientist Monica Grady from the Open University, senior astronomer Seth Shostak from SETI and zoologist Matthew Cobb from the University of Manchester.
Send your Curious Cases for consideration in to curiouscases@bbc.co.uk
Presenters: Hannah Fry, Adam Rutherford Producer: Michelle Martin.