The Planets: Aug 4

In the final episode of The Planets, Professor Brian Cox looks at the ice cold planets of Uranus and Neptune.

This is a journey into the darkness, to a place that the most mysterious planets of the
Solar System call home. They remain shadowy for a simple reason. We have visited the planets of the inner solar system multiple times over the decades and each time we have gone, our understanding has deepened. But the planets beyond Saturn have only been visited once.

The ice giant Uranus was once thought to be the furthest planet from the Sun. Then
another ice giant showed up, Neptune. Thanks to a rare alignment of the planets in 1976, Voyager 2 had a close encounter with both worlds. There we discovered far more vibrant planets than we ever imagined. Even at such cold temperatures, great storms whip around these frozen worlds that are also home to spectacular moons and intricate ring systems. After a few hours of observation at each planet, Voyager 2 left them behind and our solar system for good.

For decades that’s as far as we got, until 2015 when NASA’s New Horizons probe began its approach to the dwarf planet Pluto. Once again all our assumptions about such a distant world were wrong. Here we found a world with ice volcanoes, dunes, geysers, even a subsurface ocean. What’s more, we discovered that Pluto isn’t alone out there – there’s a plethora of weird icy companions, like Eris and Charon, which together are redefining what we mean by the word ‘planet’ and everything we thought we knew about the strange, distant reaches of our solar system.

7:40pm Sunday on ABC.