The five episodes of the series cover the usual ground but do include reasonably recent updates from scientific missions such as Juno and Cassini. Episode 1 starts close to home, covering the rocky planets. Episode 2 gets even closer, focusing exclusively on Earth and its sister planet, Mars. This recasting of Earth’s twin as Mars rather than Venus, as usual, adds welcome interest and is motivated by recent discoveries. Episodes 3 and 4 travel out to the gas giants, Jupiter, then Saturn, and finally episode 5 reaches the ice giants, plus the calling points of New Horizons, Pluto and MU69 (called Ultima Thule in the programme).
The first episode of the series asks the big question: what makes Earth so special? Of the four terrestrial planets, why is it just Earth that hosts life? Each rocky planet had an ‘Earth-like’ moment in its history, but due to a series of unfortunate events, only one experiences that moment currently. Mercury apparently formed out near the temperate orbit of Mars, but a chance encounter with another body kicked it into a tight, elliptical orbit around the Sun. Venus itself had its Earth-like moment early on, when the Sun was young and faint. It was an ocean world that got scorched in the glare of the warming Sun, turning it into a greenhouse, portrayed as a vision of hell compared with Earth’s heaven in the episode. While Venus was sweltering, Mars’s watery surface was basking in the cosy warmth of an atmosphere. But its small mass and absent global magnetic field meant its humid blanket was slowly leaking into space, turning warm, wet Mars into cold, arid and apparently lifeless Mars.
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