In 1977, just a few months after Voyager 1 and 2 began their grand tour of the solar system, Carl Sagan gave the esteemed Christmas Lectures at the Royal Institution of Great Britain. You can watch them below via YouTube or at the Royal Institution's site. Launched by Michael Faraday in 1825, the Christmas Lectures are meant to be "engaging and mind-expanding… for all ages but particularly children and young adults." As usual, Carl delivered the goods. From the Royal Institution:
Beginning with a closer look at the world we inhabit, Sagan explores of the diversity of life on our own planet and the building blocks behind it, before questioning whether the same organic chemistry is occurring on planets in the outer solar system.
In Lecture Three onwards Sagan takes a closer look at our neighbouring planet, Mars. From early interpretations of terrestrial life on its surface to the surprising discoveries made by NASA's Viking Program, the Red Planet has become the focus of efforts to discern whether intelligent life exists elsewhere in the universe.
When Sagan delivered his lectures in the late 1970s, NASA had only just begun its Voyager program to the furthest planets in our solar system and no extra-solar planets were known to exist. Now, over three decades later, astronomers are looking at planets that lie beyond our solar system to ask the very same question we pondered over Mars: is there life out there?