The worlds that surround our planet are all made of rock, but there the similarity ends. Some have a beating geological heart, others are frozen in time. Brian travels to the tallest mountain on earth, the volcano Mauna Kea on Hawaii, to show how something as basic as a planet's size can make the difference between life and death. Even on the summit of this volcano, Brian would stand in the shade of the tallest mountain in the solar system, an extinct volcano on Mars called Olympus Mons, which rises up 27 km. Yet the fifth wonder in the series isn't on a planet at all. It's on a tiny moon of Jupiter. The discoveries made on Io have been astonishing. This fragment of rock should be cold and dead, yet, with the volcanic landscape of eastern Ethiopia as a backdrop, Brian reveals why Io is home to extraordinary lakes of lava and giant volcanic plumes that erupt 500 km into the sky.
Professor Brian Cox visits some of the most stunning locations on earth to describe how the laws of nature have carved natural wonders across the solar system. Brian descends to the bottom of the Pacific in a submarine to witness the extraordinary life forms that survive in the cold, black waters. All life on Earth needs water so the search for aliens in the solar system has followed the search for water. Soaring above the dramatic Scablands of the United States, Brian discovers how the same landscape has been found on Mars. And it was all carved out in a geological heartbeat by a monumental flood. Armed with a gas mask, Brian enters a cave in Mexico where bacteria breathe toxic gas and leak concentrated acid. Yet relatives of these creatures could be surviving in newly-discovered caves on Mars. But Brian's sixth wonder isn't a planet at all. Jupiter's moon Europa is a dazzling ball of ice etched with strange cracks. The patterns in the ice reveal that, far below, there is an ocean with more potentially life-giving water than all the oceans on Earth. Of all the wonders of the solar system forged by the laws of nature, there is one that stands out. In the final episode of this series, Brian reveals the greatest wonder of them all.