Frosty Roofs, Rocks from Space and UK Quakes

In this week's Ask the Naked Scientists Dave sates your thirst for knowledge with a look at whether frozen water is safe to drink, divides fog from mist, shakes up the world of seismology with a look at how earthquakes occur in countries like the UK, works out why some roofs remain resolutely frost-free in winter and explains how rocks from Mars turn up on Earth.