Cold, arid, and tens of millions of miles away from Earth, Mars has intrigued scientists for centuries. The existence of liquid on its surface was confirmed by NASA’s flyby mission, Mariner 4, in 1965, but the question of whether life exists on our neighbouring planet has remained a subject of much speculation.
In the 19th and 20th centuries, observers using only the naked eye and a telescope saw features on Mars which they interpreted as evidence for a dry but Earth-like climate, for vegetation which grew and decayed with the seasons, and for a great Martian canal network designed by a heroic but dying race of hydraulic engineers.
In the third of his Christmas Lectures, Carl Sagan explores the mystery of the Red Planet. From its rocky craters to its polar ice caps, Sagan describes our understanding of the geology and chemistry of Mars, revealing the discovery of its two moons, Phobos and Deimos, in 1877, and the bizarre one-time suggestion that these moons were artificial satellites launched by an ancient but not extinct Martian civilisation.