Sunday, abc, 7.40pm
English professor Brian Cox (pictured) is a natural storyteller, which is a winner for viewers of his documentaries – he really does make educational topics fu n . As Cox continues his tour of the solar system with The Two Sisters – Earth and Mars, he reveals that it was once home to not one, but two blue planets. The story he tells sounds like a fairytale – two sisters, alike in many ways, take different paths, but while one flourishes, the other dies. The sisters in question are, of course, Earth and Mars. Today, Mars is an arid desert world, but it did have the same potential as Earth. Which begs a big question – was there once life on Mars?