A bunch of astrophysicists explain lots of fun things about the universe. The chance of alien life. The chance of knowing about alien life. The weather on Jupiter's moons. How windy are other planets. What to fear. Why a solar flare could change the course of history. There are lots of clips of artists impressions of what planetary collisions might have looked like. These are repeated incessantly. Some rather amateur films of things being burnt to explain the effect of 800 degrees centigrade. On the one hand it is done with great enthusiasm by people who seem genuinely interested and knowledgeable. On the other it is stretched out too far, the same concept repeated over and over using the same graphics. This can be said of most Horizon episodes. Would have been a 5 star if it had been condensed into 1 episode.