Titan sub and an HIV vaccine

Dr Chris Smith and the Naked Scientist team present the latest science news, analysis and breakthroughs.In today's programme: The missing Titan sub might have imploded - we look at the conditions that the vehicle - and would be rescuers - were having to work with 4km down. Also, we discuss the telescope heading for space to shed new light on dark energy.Plus, 40 years on since the identification of HIV we look at where this virus came from, and how far away we are from an effective vaccine.Get the podcast from the BBC Sounds app.