Melvyn Bragg and guests discuss the planet Saturn with its rings of ice and rock and over 60 moons. In 1610, Galileo used an early telescope to observe Saturn, one of the brightest points in the night sky, but could not make sense of what he saw: perhaps two large moons on either side. When he looked a few years later, those supposed moons had disappeared. It was another forty years before Dutch scientist Christiaan Huygens solved the mystery, realizing the moons were really a system of rings. Successive astronomers added more detail, with the greatest leaps forward in the last forty years. The Pioneer 11 spacecraft and two Voyager missions have flown by, sending back the first close-up images, and Cassini is still there, in orbit, confirming Saturn, with its rings and many moons, as one of the most intriguing and beautiful planets in our Solar System. WithCarolin Crawford Public Astronomer at the Institute of Astronomy and Fellow of Emmanuel College, University of CambridgeMichele Dougherty Professor of Space Physics at Imperial College LondonAndAndrew Coates Deputy Director in charge of the Solar System at the Mullard Space Science Laboratory at UCL.

Melvyn Bragg and guests discuss the eminent 19th-century scientist Michael Faraday. Born into a poor working-class family, he received little formal schooling but became interested in science while working as a bookbinder's apprentice. He is celebrated today for carrying out pioneering research into the relationship between electricity and magnetism. Faraday showed that if a wire was turned in the presence of a magnet or a magnet was turned in relation to a wire, an electric current was generated. This ground-breaking discovery led to the development of the electric generator and ultimately to modern power stations. During his life he became the most famous scientist in Britain and he played a key role in founding the Royal Institution's Christmas lectures which continue today.With:Geoffrey Cantor Professor Emeritus of the History of Science at the University of LeedsLaura Herz Professor of Physics at the University of OxfordFrank James Professor of the History of Science at the Royal InstitutionProducer: Victoria Brignell.

Melvyn Bragg and his guests discuss the evolution and role of Circadian Rhythms, the so-called body clock that influences an organism's daily cycle of physical, behavioural and mental changes. The rhythms are generated within organisms and also in response to external stimuli, mainly light and darkness. They are found throughout the living world, from bacteria to plants, fungi to animals and, in humans, are noticed most clearly in sleep patterns. WithRussell Foster Professor of Circadian Neuroscience at the University of OxfordDebra Skene Professor of Neuroendocrinology at the University of SurreyAndSteve Jones Emeritus Professor of Genetics at University College London.

Melvyn Bragg and guests discuss the problem of P versus NP, which has a bearing on online security. There is a $1,000,000 prize on offer from the Clay Mathematical Institute for the first person to come up with a complete solution. At its heart is the question "are there problems for which the answers can be checked by computers, but not found in a reasonable time?" If the answer to that is yes, then P does not equal NP. However, if all answers can be found easily as well as checked, if only we knew how, then P equals NP. The area has intrigued mathematicians and computer scientists since Alan Turing, in 1936, found that it's impossible to decide in general whether an algorithm will run forever on some problems. Resting on P versus NP is the security of all online transactions which are currently encrypted: if it transpires that P=NP, if answers could be found as easily as checked, computers could crack passwords in moments.With Colva Roney-Dougal Reader in Pure Mathematics at the University of St AndrewsTimothy Gowers Royal Society Research Professor in Mathematics at the University of CambridgeAnd Leslie Ann Goldberg Professor of Computer Science and Fellow of St Edmund Hall, University of OxfordProducer: Simon Tillotson.

Melvyn Bragg and guests discuss the rise of the idea of perpetual motion and its decline, in the 19th Century, with the Laws of Thermodynamics. For hundreds of years, some of the greatest names in science thought there might be machines that could power themselves endlessly. Leonardo Da Vinci tested the idea of a constantly-spinning wheel and Robert Boyle tried to recirculate water from a draining flask. Gottfried Leibniz supported a friend, Orffyreus, who claimed he had built an ever-rotating wheel. An increasing number of scientists voiced their doubts about perpetual motion, from the time of Galileo, but none could prove it was impossible. For scientists, the designs were a way of exploring the laws of nature. Others claimed their inventions actually worked, and promised a limitless supply of energy. It was not until the 19th Century that the picture became clearer, with the experiments of James Joule and Robert Mayer on the links between heat and work, and the establishment of the First and Second Laws of Thermodynamics.With Ruth Gregory Professor of Mathematics and Physics at Durham UniversityFrank Close Professor Emeritus of Physics at the University of OxfordandSteven Bramwell Professor of Physics and former Professor of Chemistry at University College LondonProducer: Simon Tillotson.

In 1977, scientists in the submersible "Alvin" were exploring the deep ocean bed off the Galapagos Islands. In the dark, they discovered hydrothermal vents, like chimneys, from which superheated water flowed. Around the vents there was an extraordinary variety of life, feeding on microbes which were thriving in the acidity and extreme temperature of the vents. While it was already known that some microbes are extremophiles, thriving in extreme conditions, such as the springs and geysers of Yellowstone Park (pictured), that had not prepared scientists for what they now found. Since the "Alvin" discovery, the increased study of extremophile microbes has revealed much about what is and is not needed to sustain life on Earth and given rise to new theories about how and where life began. It has also suggested forms and places in which life might be found elsewhere in the Universe. With Monica Grady Professor of Planetary and Space Sciences at the Open UniversityIan Crawford Professor of Planetary Science and Astrobiology at Birkbeck University of LondonAndNick Lane Reader in Evolutionary Biochemistry at University College LondonProducer: Simon Tillotson.

While glass items have been made for at least 5,000 years, scientists are yet to explain, conclusively, what happens when the substance it's made from moves from a molten state to its hard, transparent phase. It is said to be one of the great unsolved problems in physics. While apparently solid, the glass retains certain properties of a liquid. At times, ways of making glass have been highly confidential; in Venice in the Middle Ages, disclosure of manufacturing techniques was a capital offence. Despite the complexity and mystery of the science of glass, glass technology has continued to advance from sheet glass to crystal glass, optical glass and prisms, to float glasses, chemical glassware, fibre optics and metal glasses.With:Dame Athene Donald Professor of Experimental Physics at the University of Cambridge and Master of Churchill College, CambridgeJim Bennett Former Director of the Museum of the History of Science at the University of Oxford and Keeper Emeritus at the Science MuseumPaul McMillan Professor of Chemistry at University College LondonProducer: Simon Tillotson.

Melvyn Bragg and his guests discuss the Earth's Core. The inner core is an extremely dense, solid ball of iron and nickel, the size of the Moon, while the outer core is a flowing liquid, the size of Mars. Thanks to the magnetic fields produced within the core, life on Earth is possible. The magnetosphere protects the Earth from much of the Sun's radiation and the flow of particles which would otherwise strip away the atmosphere. The precise structure of the core and its properties have been fascinating scientists from the Renaissance. Recent seismographs show the picture is even more complex than we might have imagined, with suggestions that the core is spinning at a different speed and on a different axis from the surface.WithStephen Blundell Professor of Physics and Fellow of Mansfield College at the University of OxfordArwen Deuss Associate Professor in Seismology at Utrecht UniversityandSimon Redfern Professor of Mineral Physics at the University of CambridgeProducer: Simon Tillotson.

Melvyn Bragg and his guests discuss the scientific achievements of the Curie family. In 1903 Marie and Pierre Curie shared a Nobel Prize in Physics with Henri Becquerel for their work on radioactivity, a term which Marie coined. Marie went on to win a Nobel in Chemistry eight years later; remarkably, her daughter Irène Joliot-Curie would later share a Nobel with her husband Frédéric Joliot-Curie for their discovery that it was possible to create radioactive materials in the laboratory. The work of the Curies added immensely to our knowledge of fundamental physics and paved the way for modern treatments for cancer and other illnesses.With:Patricia Fara Senior Tutor of Clare College, University of CambridgeRobert Fox Emeritus Professor of the History of Science at the University of OxfordSteven T Bramwell Professor of Physics and former Professor of Chemistry at University College LondonProducer: Simon Tillotson.

Melvyn Bragg and his guests discuss dark matter, the mysterious and invisible substance which is believed to make up most of the Universe. In 1932 the Dutch astronomer Jan Oort noticed that the speed at which galaxies moved was at odds with the amount of material they appeared to contain. He hypothesized that much of this 'missing' matter was simply invisible to telescopes. Today astronomers and particle physicists are still fascinated by the search for dark matter and the question of what it is.With Carolin Crawford Public Astronomer at the Institute of Astronomy, University of Cambridge and Gresham Professor of AstronomyCarlos Frenk Ogden Professor of Fundamental Physics and Director of the Institute for Computational Cosmology at the University of DurhamAnne Green Reader in Physics at the University of NottinghamProducer: Simon Tillotson.