Multiprobe Exploration of the Giant Planets – Shallow Probes

Comparative planetology of the giant planets is key to the origin and evolution of the solar system and, by extension, extrasolar systems. In particular, elemental composition of well-mixed atmospheres is the most critical measurement, but it is also most challenging. This is because the well-mixed region for certain species lies well below the clouds, a deep region where measurements are difficult to make and the data are hard to transmit from. Here we discuss a new approach, which combines microwave radiometry with shallow entry probes, that could alleviate much of these problems. At Saturn and Jupiter, the probes need to be deployed to only about 10 bars. At the ice-giants, Uranus and Neptune, neither probes – even deep probes – nor radiometry would be of much help in determining the elemental abundance of oxygen, and possibly nitrogen. However, the lack of determination of O/H and N/H at Uranus and Neptune is not detrimental, provided that all other critical elements have been measured and compared with those on the gas giants. Therefore probes to 10 bars, with a maximum to 50 bars would be sufficient at the ice giants. At these depths, all critical elements, except O and N can be accessed. We recommend multiple probes at each of the giant planets, together with microwave radiometry from flyby or orbiter spacecraft. The value of microwave radiometry at Uranus and Neptune requires further study. It is quite conceivable that the first such mission – a Saturn flyby with probes and microwave radiometry – could be ready in the near short term within the cost cap of NASA's New Frontiers class. Multinational partnerships are desirable for the highest science return as well as possible cost savings.