Scientists have long been fascinated by the prospect of life on Mars - but how can we begin to look for life on a planet which has a much thinner atmosphere and much lower temperatures than our own?   One method, currently being researched by The Open University's Dr Mario Toubes-Rodrigo, is to grow the micro-organisms of very salty lakes here on Earth and analyse the gases they produce, which are then in turn compared with potential bio-signatures in the Martian atmosphere.   Writer and Science Communicator Dr Natalie Starkey caught up with Mario to find out more about what is becoming a fascinating area of research.