Scientists have been testing whether life exists on Mars for over 40 years, ever since the Viking 1 lander touched down on the Red Planet. Researchers often perform experiments on Earth to better understand the context of data collected by Viking 1 and subsequent landers – data that gives scientists tantalizing clues about the habitability of the Martian surface.

In this episode, Los Alamos National Laboratory researchers Nina Lanza and Chris Yeager discuss their investigations into rock varnish in New Mexico, which could help them understand whether life is present on Mars. Rock varnish is a mysterious coating found on rocks in some of the harshest and most Mars-like landscapes on Earth, but no one knows whether rock varnish is created by living things. If so, finding it on Mars would be a sign that Martian life exists now or has existed in the past.

This episode was produced by Larry O'Hanlon and mixed by Kayla Surrey.