The comparative exploration of the ice giant planets with twin spacecraft: Unveiling the history of our Solar System

Abstract

In the course of the selection of the scientific themes for the second and third L-class missions of the Cosmic Vision 2015-2025 program of the European Space Agency, the exploration of the ice giant planets Uranus and Neptune was defined "a timely milestone, fully appropriate for an L class mission". Among the proposed scientific themes, we presented the scientific case of exploring both planets and their satellites in the framework of a single L-class mission and proposed a mission scenario that could allow to achieve this result. In this work we present an updated and more complete discussion of the scientific rationale and of the mission concept for a comparative exploration of the ice giant planets Uranus and Neptune and of their satellite systems with twin spacecraft. The first goal of comparatively studying these two similar yet extremely different systems is to shed new light on the ancient past of the Solar System and on the processes that shaped its formation and evolution. This, in turn, would reveal whether the Solar System and the very diverse extrasolar systems discovered so far all share a common origin or if different environments and mechanisms were responsible for their formation. A space mission to the ice giants would also open up the possibility to use Uranus and Neptune as templates in the study of one of the most abundant type of extrasolar planets in the galaxy. Finally, such a mission would allow a detailed study of the interplanetary and gravitational environments at a range of distances from the Sun poorly covered by direct exploration, improving the constraints on the fundamental theories of gravitation and on the behaviour of the solar wind and the interplanetary magnetic field.

Gravitational anomalies in the solar system?

“…Also in this case, its alleged impact on planetary orbital motions was ruled out by a comparison with the observations. 265 As outlined in Section 2, dedicated planetary missions 123,124,127 to the outermost icy gaseous giants of the Solar system would allow to greatly improve their orbital determination, thus allowing for much more stringent tests of the PA-and, more generally, of gravitational theories-in the far regions of the Sun's realm.…”

Is the Recently Proposed Mars-Sized Perturber at 65–80 AU Ruled Out by the Cassini Ranging Data?

“…Dedicated analyses by reprocessing existing Cassini data would allow for a more rigorous analysis. Furthermore, it is worth noticing that new missions towards the ice giants (Arridge et al 2012(Arridge et al , 2014Turrini et al 2014;Hofstadter & et al 2017) would be beneficial in order to get better constraints on the mass distribution in the distant regions of the Solar System.…”

Future Missions to the Giant Planets that Can Advance Atmospheric Science Objectives

“…Since the science case for such a mission remains strong, and the outer planet community (as represented by NASA's Outer Planets Assessment Group, or OPAG) continues to support an Ice Giant mission, there is a good chance a Uranus or Neptune mission will figure prominently in the next Decadal Survey as well. Furthermore, European scientists have continued to express a strong desire for both orbital Ice Giant exploration (Arridge et al, 2012(Arridge et al, , 2014Masters et al, 2014;Turrini et al, 2014) and in situ entry probes (Mousis et al, 2018). The Uranus Pathfinder orbital concept was proposed to both the M3 and M4 calls (Arridge et al, 2012(Arridge et al, , 2014, a Neptune mission was also proposed to M3 (OSS, Christophe et al 2012), and Ice Giants featured strongly when ESA called for scientific themes for its L2 and L3 launch opportunities in 2013.…”

“…Complicating the decision about which Ice Giant to target is the exciting opportunity to visit both planets utilizing two spacecraft (Turrini et al 2014;Simon et al 2018). (The orbital positions of the planets will not allow a single spacecraft to visit both planets-as Voyager did in the 1980's-for another ~150 years.)…”