Comparative planetary science closest analogue is the Pluto-Charon system, though its axial tilt is completely different. Both our Moon and Charon are hypothesized to have formed via giant impacts. Giant impacts are hypothesized to account for both the tilt of Uranus, and the retrograde rotation of Venus. Giant impacts are also candidates for the Mars ocean hypothesis, and the high density of Mercury. Most giant planets (except Neptune) have retinues of moons, rings, ring shepherds, and moon Trojans analogous to mini-solar systems. These systems are postulated to have accreted from analogous gas clouds, and possibly with analogous migrations during their formation periods. The
Wonders of the Solar System as mapped on the Hertzsprung–Russell diagram. Cox starts this episode in Al-Qayrawan, Tunisia to analyse the orbit of the planets around our Sun, with details on how the 23 degree tilt of the Earth creates the seasonal weather patterns. He also visits the Atlas Mountains, and relates how in clear night skies the ancients observed the rotation of the stars and the retrograde and prograde motion of Mars and the other wandering planets. In Oklahoma, US, he discusses the universal reach of the Coriolis effect and the importance of the conservation of angular momentum. Next, at the Jet Propulsion Laboratory