We know that distant galaxies are racing away from us. But just how fast is the Universe expanding? Scientists are yet to agree on an answer. Show more

Comets and asteroids have been witnessed in our skies for millennia, but only now can we see these tiny, mysterious worlds up close. What will the next one bring us? Show more

With the dream of sending humans to Mars closer than ever before, Horizon asks the world's leading experts on Mars where they would go and what they would need to survive. Show more