In this book, we have discussed how the giant planets and their atmospheres formed 4.6 billion years ago and have reviewed what is known about their atmospheres from existing measurements, models, and theory. The story of the way in which our understanding of these giant worlds has advanced is essentially one of how improvements in technology have allowed more and more detailed observations of these worlds, which in turn have allowed more advanced and accurate analysis. The rate of improvement in these data has rapidly increased with time, and thus we have learned more about these worlds in the last 25 years than in all of the previous centuries put together! Technology continues to develop at an extraordinary rate, and thus many exciting new measurements are expected in the next few years which will further improve our understanding of these giant worlds, and how they formed from circumplanetary disks. Some of the key questions concerning the atmospheres of the giant planets that still remain are
• What are the upper visible clouds of Jupiter and Saturn actually composed of when the spectral signature of ammonia ice seems to be generally so elusive?
• What actually is the composition of the main cloud deck on Uranus and Neptune?
• What is the nature of the chromophores on the different giant planets?
• To what level are different heavy elements enriched on the giant planets and how did the observed differences come about?
• What is the enrichment of heavy elements other than carbon on Uranus and Neptune?
• Were the heavy elements introduced to the giant planet atmospheres through amorphous or crystalline water ice?
• Why is ammonia so scarce down to several tens of bars on Uranus and Neptune and why does it appear depleted in the upper atmosphere of Jupiter?
• Is there really N2 in the atmosphere of Neptune and what are the abundances of other disequilibrium species on the ice giants?
• Why does Uranus have such a small source of internal energy?
• Why do Jupiter and Saturn have strong prograde equatorial jets, while Uranus and Neptune have retrograde jets?
• Why are almost all of the large ovals on the giant planets anticyclonic?
• Is the structure of our solar system actually typical compared with other star systems, or is it in some way unusual?
The list could go on and on since, although we have already learned a huge amount, we have only just begun to really understand the atmospheres of these planets. In this chapter we will review the likely projects in the next ten years, which should have major impacts on our understanding of these worlds. Major developments are expected in the fields of space-based telescopes, ground-based telescopes, and spacecraft missions. Further in the future, missions are currently being planned to search for planets about other stars, which should allow us to understand better the structure of our own solar system and how it most likely formed and evolved.
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