Volcanoes here on Earth are pretty crazy – but did you know that even wilder versions are merrily bubbling away in space? This Horizon documentary introduces us to the international team of volcanologists who are researching the parallels between our own volcanoes and those around the solar system – the Olympus Mons on Mars, for example, is the solar system’s largest volcano and shares similarities with those in Iceland. Incredible, mind-boggling stuff.