Wonders of the Solar System on the matter that composite the rings - a phenomenon called orbital resonance. The third episode looks at the atmosphere of the planets and moons of the Solar System, with Earth, Mars, and Venus being the main focus. The episode starts with Cox travelling to South Africa and taking a journey in an English Electric Lightning up to an altitude of 18 kilometres where the "thinness and fragility" of the atmosphere could be observed in the middle of the day. This is then contrasted with the planet-wide consequences of Mercury's depleted, and Venus' broiling greenhouse atmospheres. Later, the dunal morphology
Moons of Neptune formed "in situ". Triton and Nereid are unusual irregular satellites and are thus treated separately from the other five irregular Neptunian moons, which are more like the outer irregular satellites of the other outer planets. Firstly, they are the largest two known irregular moons in the Solar System, with Triton being almost an order of magnitude larger than all other known irregular moons. Secondly, they both have atypically small semi-major axes, with Triton's being over an order of magnitude smaller than those of all other known irregular moons. Thirdly, they both have unusual orbital eccentricities: Nereid has one of the