In 2014, the International Space Station had to move three times to avoid lethal chunks of space debris and there is an increasing problem of satellites mysteriously breaking down. With first-hand accounts from astronauts and experts, know the scale of the problem of space junk. Our planet is surrounded by hundreds of millions of pieces of junk moving at 17,000 miles per hour. Now the US government is investing a billion dollars to track them, and companies around the world are developing ways to clear up their mess - from robot arms to nets and harpoons. Learn the science behind the hit film Gravity and discovers the reality is far more worrying than the Hollywood fiction.

Al-Khalili travels to northern Syria to discover how, a thousand years ago, the great astronomer and mathematician Al-Biruni estimated the size of the earth to within a few hundred miles of the correct figure. He discovers how medieval Islamic scholars helped turn the magical and occult practice of alchemy into modern chemistry. In Cairo, he tells the story of the extraordinary physicist Ibn al-Haytham, who helped establish the modern science of optics and proved one of the most fundamental principles in physics - that light travels in straight lines. Prof Al-Khalili argues that these scholars are among the first people to insist that all scientific theories are backed up by careful experimental observation, bringing a rigour to science that didn't really exist before.

What if we could explore the vastness of Space? Science fiction has always fed upon our need to explore – to wonder what is out there. Space journeys from Jules Verne’s earliest ideas about attempts to leave our planet, to the Star Wars far away galaxy through to Nichelle Nichols revealing how her groundbreaking role as Lt. Uhura in Star Trek led to her participation in the recruitment of NASA’s astronauts. It explores the deep sea inspiration for Avatar, finds out why Ursula K Le Guin wrote The Left Hand of Darkness and discovers how Stanley Kubrick was able to make 2001: A Space Odyssey seem so believable. In addition, the program looks at the way Dune and The Mars Trilogy embraced the challenge of world building and discusses the appeal of the beaten up ‘dirty space’ of Dark Star and Firefly. From the horrifying scenes of Alien, to the epic spectacle of Star Wars, this is a journey to the stars and the alien encounters that await us there.

When a mysterious cigar-shaped object is spotted tumbling through our solar system, experts race to uncover it's true nature. The object, nicknamed Oumuamua, meaning 'a messenger that reaches out from the distant past' in Hawaiian, was discovered by the Pan-STARRS 1 telescope in Hawaii. Since its discovery, scientists have been at odds to explain its unusual features and precise origins, with researchers first calling it a comet and then an asteroid before finally deeming it the first of its kind: a new class of 'interstellar objects.'
A recent paper by researchers at the Harvard Smithsonian Center for Astrophysics raises the possibility that the elongated dark-red object, which is 10 times as long as it is wide and travelling at speeds of 196,000 mph, might have an 'artificial origin.' The theory is based on the object's 'excess acceleration,' or its unexpected boost in speed as it travelled through and ultimately out of our solar system.

On July 4, 2012, scientists at the giant atom smashing facility at CERN announced the discovery of a subatomic particle that seems like a tantalizingly close match to the elusive Higgs Boson, thought to be responsible for giving all the stuff in the universe its mass. Since it was first proposed nearly fifty years ago, the Higgs has been the holy grail of particle physicists: finding it completes the 'standard model" that underlies all of modern particle physics. Now CERN's scientists are preparing for the Large Hadron Collider's second act, when they restart the history-making collider, running at higher energy--hoping to find the next great discovery that will change what we know about the particles and forces that make up our universe.

Having explained the science behind global warming, and addressed the arguments of the climate change sceptics earlier in the series, Dr Iain Stewart concludes the series by looking at the biggest challenge now facing climate scientists - Just how can they predict exactly what changes global warming will bring?
It's a journey that takes him from early attempts to model the climate system with dishpans, to supercomputers, and to the frontline of climate research today: Greenland. Most worryingly he discovers that scientists are becoming increasingly concerned that their models are actually underestimating the speed of changes already underway.