Space Odyssey: Voyage to the Planets

To accompany Space Odyssey: Voyage To The Planets, BBC FOUR broadcasts a documentary that looks at the history of space exploration to reveal the science behind the series. It tells the story of the human ingenuity that has dispatched robotic missions to all the planets except, as yet, Pluto. Voyager 2 - which accomplished the original grand tour of the planets in the Seventies and Eighties - is a prime example. Incredibly, more than 25 years since its launch and now over seven billion miles from Earth, we can still hear its whispers from deep space. It carries the spirit of human exploration like a metal Christopher Columbus as its sensors probe the edge of our planetary system.

The interplanetary spacecraft Pegasus and her five-strong crew are launched into Earth orbit. Their epic six-year mission has begun. Forty one days from Earth lies their first encounter - with Venus. Although Earth's nearest neighbour, it could not be a more different world. With clouds of sulphuric acid, surface temperatures pushing 500 degrees centigrade, snows of metal encrusting mountain peaks and atmospheric pressures that could destroy a submarine, this is a hell-hole of a planet. Astronauts Zoe Lessard and Yvan Grigorev make the nail-biting descent in a landing craft called Orpheus.

Just over 200 days of travel from the Sun, Pegasus reaches the largest planet of the solar system, Jupiter. Its danger lies in a menace lurking at its core - a churning mass of liquid metallic hydrogen that inflates a magnetic bubble around the planet, producing levels of radiation 500 times the dose that would kill a human. To repel these lethal rays, Pegasus generates its own magnetic field. Mission geologist Zoe is to land on Io, one of Jupiter's moons. As the most volcanically active world in the solar system, it's a geologist's heaven.