The planets – Mars after Viking (1977)

Carl Sagan

Carl Sagan asks, is there life on Mars?

Watch time: 59:34
Carl Sagan smiling with audience of children during CHRISTMAS LECTURES
Credit: Royal Institution

Lecture 5 - Mars after Viking

In his fifth lecture, Carl Sagan takes a look at the design, launch and accomplishments of the Viking mission, a major chapter in the history of planetary exploration.

After Mariner 9's remote orbital inspection of Mars, the Viking program finally allowed scientists to study the Martian surface in detail. The photography of the terrain, the chemical analysis of the soil and testing for microbiological life yielded stunning, yet enigmatic results.

Results returned from the microbiology experiments gave signs consistent with life, however, the search for organic molecules in the Martian soil turned up completely negative. The conflict between these results suggested either the presence of microbiological life or a non-biological, inorganic process occurring within the Martian soil.

Four decades later – following the success of subsequent Mars rovers – the question concerning life on Mars is one that still remains unanswered.


What exists beyond Earth? Over six Lectures presented in 1977, American astronomer and cosmologist Carl Sagan explores the vast expanse of space that surrounds the third planet from the Sun.

Life on Earth

Where at first we could only discern the size of our planet and some knowledge of its atmosphere and configuration, the evolution of planetary exploration has revealed not only intricate details of Earth’s climate and geology, but a multitude of stars and planets besides our own.

Beginning with a closer look at the world we inhabit, Carl 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.

The Red Planet

In Lecture three onwards, Carl 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 Carl 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?