Perseverance rock drop: 'This is a really big deal'
Nasa's Perseverance Mars rover is about to build a cache of rocks on the ground for later return to Earth. The materials have been packaged in small titanium tubes with the expectation they can be picked up by a future mission and brought home. It's a major milestone in the quest to find out whether there is life on Mars. Nasa's director of planetary science, Lori Glaze, spoke with our science correspondent Jonathan Amos.
