Are we alone in the universe? Right now we are in a period of unprecedented change that is taking us closer than ever to answering this fundamental question. A dizzying array of planets are being discovered orbiting alien stars and we've developed instruments so sensitive we can detect the weather systems on these new worlds. But do any harbour life? Geneticist Dr Adam Rutherford seeks to define what life is and Maggie Aderin-Pocock explores our chances of finding it in the universe.

t is one of the most extraordinary space adventures in a generation - to land a spacecraft on a comet.

The European Space Agency's (ESA) Rosetta spacecraft has been hurtling through space for over 10 years, tracking down a comet called 67P/Churyumov-Gerasimenko. Now it is about to do something that has never been attempted before and land a spacecraft on the comet's surface.

This special episode of The Sky at Night puts the viewer right at the heart of the action, witnessing events as they happened from inside mission control. It reveals the latest images, explores the first groundbreaking science coming back from the comet and asks the astonishing questions that make this mission so captivating. Could Earth's water have come from comets? How do comets survive for so long? Could they have triggered the start of life on Earth?

The journey has been fraught with risk and at every stage the comet seems to surprise, but if the mission succeeds it will be a momentous day in the history of space exploration.