The planets – Mars before Viking (1977)

Carl Sagan

Carl Sagan views Mars through the eyes of Mariner 9.

Watch time: 59:43
A still of Carl Sagan during his CHRISTMAS LECTURE in 1977
Credit: Royal Institution

Lecture 4 - Mars before Viking

Observing the planets in our solar system from Earth provided limited scope for astronomers wishing to explore them in more detail. To get a better understanding of planets such as Mars, astronomers needed to get a closer look through the use of unmanned space probes which could beam data back remotely.

In this Lecture, Carl Sagan explores the surprising discoveries made by Mariner 9, the first unmanned space probe to orbit another planet. This mission went on to provide scientists with a glimpse at Mars that was wildly different from their expectations.

Carl explores the features of Mars as uncovered by Mariner 9, including the formation of craters, presence of volcanoes, polar regions and the significance of its winding sinuous valleys and tributaries.

These findings point towards a planet that has undergone considerable climate change, with early evidence that it might once have been conducive to terrestrial life.


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?