How were new craters on Mars discovered?

When a space rock smashes into the surface of a planet, a hole - or crater - is formed. New craters might be relatively straightforward to identify on Earth, but what about on other planets, such as Mars? In this episode we hear from Dr Ben Fernando, a researcher from Oxford's Department of Physics and a scientist on NASA's InSight mission, about the techniques used to discover new craters on the red planet.