In this module, you left behind the Earth and the other planets that are either too close to the Sun or too small to be habitable. At Jupiter and Saturn, you encountered conditions so extreme that no probe can survive long inside them. In fact, the final act of several missions — including Galileo at Jupiter and Cassini at Saturn — was to dive intentionally into their atmospheres, erasing any trace of the spacecraft to avoid contaminating nearby moons that might harbour life.
Despite their hostile environments, astronomers are deeply interested in studying Jupiter and Saturn for two main reasons. The first, which you explored throughout this module, involves their moons. Discoveries made over the past two decades have completely reshaped our understanding of what it means for a world to be habitable. For example, Titan has no liquid water on its surface, yet it hosts vast methane–ethane lakes. We know that life on Earth depends on liquid water, but we do not yet know why water — specifically H2O — is essential. Could another liquid play a similar role elsewhere? If so, Titan might be a prime candidate for an alternative form of life. And if the answer is no — if liquid water is uniquely necessary — then we already have two strong candidates, Europa and Enceladus, where water, organic molecules, and internal heat all coexist, providing the essential ingredients for life as we know it.
The second major reason for studying Jupiter and Saturn, as highlighted in the Juno mission work you completed, is that these two planets are thought to have been the first worlds to form in our Solar System. Understanding their composition, structure, and evolution gives scientists valuable clues about how planetary systems originate — not only our own, but those now being discovered around other stars. By exploring their atmospheres, magnetic fields, and deep interiors, missions like Juno, along with future explorers such as Europa Clipper, JUICE, and Dragonfly, continue to reveal how the building blocks of planets and life itself came together.
In Module 10, you will investigate the details of current theories about the formation and evolution of planetary systems, and examine the evidence that supports them. But before we turn to those broad origins, we’ll take one more step outward — to the planets and icy worlds that lie beyond Saturn. In the next module, you’ll meet Uranus, Neptune, and the Kuiper Belt objects that were only discovered with the aid of the telescope, completing your tour of the Solar System’s outer frontier.
cosmiCave.org 