Ice Giant Study


The ice giant planets, Uranus and Neptune, represent one of the frontiers of solar system exploration. So far they have only been visited in the mid-1980s by the Voyager 2 spacecraft, which showed that they are a distinct class of planets. Uranus and Neptune have compositions that are very different from Jupiter and Saturn, being largely composed of "ices" (volatile elements heavier than hydrogen and helium). This results in their blue colour.


There are many open questions about how these distant planetary systems work, what role they played in solar system formation, and what they can tell us about exoplanets orbiting other stars. For example, the reason why there is so little heat coming from Uranus' core is unknown, and why Neptune has the most dynamic atmosphere in the Solar System is also currently under debate. Also unclear is how Uranus' satellite system survived the event that tilted the rotation axis of the planet, how Triton became a moon of Neptune, and where Triton originated before its capture.


In 2013, ESA called for white papers for the definition of the science themes to be addressed by the future "Large" L2 and L3 missions in the ESA Cosmic Vision Programme. Three white papers on ice giant planetary science were submitted by the community, presenting a Uranus mission with an orbiter and atmospheric descent probe, a mission to Neptune and Triton that also comprised a planetary orbiter, and a mission with twin orbiters to both ice giants. The Senior Survey Committee (SSC) for the selection of the science themes for the L2 and L3 launch opportunities in the Cosmic Vision Programme (see SSC's Report) did not recommend the study of the icy giants for L2 or L3, but considered it to be a theme of very high science quality and perfectly fitting the criteria for an L-class mission. In view of its importance, the SSC recommended that every effort is made to pursue this theme through other means, such as cooperation on missions led by partner agencies. A Uranus Pathfinder mission concept was also proposed to ESA in the frame of M-class mission calls. 


In January 2016 NASA formed an Ice Giant Science Definition Team (SDT), tasked with taking a fresh look at science priorities and concepts for missions to the Uranus and Neptune systems. Upon invitation by NASA, ESA appointed two European scientists to participate in the activities of the NASA Ice Giant SDT, Dr. Diego Turrini, Institute for Space Astrophysics and Planetology INAF-IAPS, Italy, and Dr. Adam Masters, Imperial College London, UK.


The SDT study has been completed, and the final report is publicly available at: