Every year, over a thousand climbers try to reach the summit of Mount Everest, with the annual record for successful attempts currently standing at 633. But of that number, nearly half were Sherpas - the mountain's unsung heroes. Yet the Sherpa community has remained secretive about their nation, culture and experiences living in the shadow of the world's highest mountain. Now, for the first time, they open the door into their world. Without the expertise of the Sherpas, only the hardiest and most skilful climbers would succeed. Every day they risk their lives for the safety of others, yet they seek neither glory nor reward, preferring to stay in the background. Following the stories of four such Sherpas - Phurba, Ngima, Ngima Tenji and Gelu - this film reveals the reality of their daily lives, not just up the mountain, but with their families after they return home.

In this episode, Helen seeks out the colours that turned planet Earth multicoloured. To investigate the essence of sunlight Helen travels to California to visit the largest solar telescope in the world. She discovers how the most vivid blue is formed from sulfur atoms deep within the Earth's crust and why the presence of red ochre is a key sign of life. In gold, she discovers why this most precious of metals shouldn't even exist on the surface of the planet and in white, Helen travels to one of the hottest places on Earth to explore the role salt and water played in shaping planet Earth.

Comet ISON can well be the brightest and most spectacular comet for a generation. It appeared above the eastern horizon from December 2013 as a glorious streak across the sky. ISON has been travelling towards the sun for ten thousand years and will make only one orbit through its corona before disappearing off into the outer solar system.
But as well as providing a great spectacle, ISON's tail of vaporised gas and water, hundreds of millions of kilometres long, will give insights into some of the greatest mysteries of science; it will help explain the origins of the solar system, whether earth's water was delivered on comets and even whether we are alone in the universe.

Minerva B is a small rocky planet just like earth, where spacecraft Artemis has found water, organic molecules, and complex creatures. Is there something more to find?
'I am the mind of the spaceship, alone among the stars. 50 years ago, from a planet far away, the planet you call home, I launched. A journey of 28 trillion miles across the yawning time of space to the exoplanet, Minerva B: a small, rocky planet, much like Earth, but orbiting another sun. Here, I have found water, organic molecules, and microorganisms. When the news of my discovery reaches Earth years from now, some of you will be amazed. But others will remain unsatisfied, and you will ask, have I not found animals or birds? Have I not met intelligent life like us? And so, my search continues. I will find life of marvellous complexity, and the traces of a devastating loss.'

A variety of cosmic events have both helpful and harmful effects on life on Earth. From the beauty of the Aurora Borealis and rainbows to the dangers of UV radiation and cosmic rays, from the miracle of photosynthesis to the thrill of a meteor shower, this episode explores how the effects generated by the sun and other extra-solar sources can literally get under our skin, scramble our technology, make life possible and threaten our existence all at the same time

They're the cooling corpses of stars like our sun, but new research proves white dwarfs are one of the driving forces of our universe. And they can tell us literally about the nature of the cosmos itself. Have scientists finally discovered how these small stars could be such massive galactic players?