Keys of a Mission to Uranus or Neptune, the Closest Ice Giants

TL;DR

Exploring Uranus and Neptune through dedicated missions is crucial for understanding ice giants' atmospheres, composition, and evolution, which in turn informs planetary science and exoplanet studies.

Contribution

This paper emphasizes the importance of missions to Uranus and Neptune, highlighting the need for orbiters and probes to study their atmospheres, gravity, and magnetic fields.

Findings

Mapping temperature and methane abundance reveals convection patterns.

Probes can determine noble gas abundances to trace planet formation.

Gravity and magnetic field data constrain planetary structure and evolution.

Abstract

Uranus and Neptune are the archetypes of "ice giants", a class of planets that may be among the most common in the Galaxy. They hold the keys to understand the atmospheric dynamics and structure of planets with hydrogen atmospheres inside and outside the solar system; however, they are also the last unexplored planets of the Solar System. Their atmospheres are active and storms are believed to be fueled by methane condensation which is both extremely abundant and occurs at low optical depth. This means that mapping temperature and methane abundance as a function of position and depth will inform us on how convection organizes in an atmosphere with no surface and condensates that are heavier than the surrounding air, a general feature of giant planets. Owing to the spatial and temporal variability of these atmospheres, an orbiter is required. A probe would provide a reference atmospheric profile to lift ambiguities inherent to remote observations. It would also measure the abundances of noble gases which can be used to reconstruct the history of planet formation in the Solar System. Finally, mapping the planets' gravity and magnetic fields will be essential to constrain their global composition, atmospheric dynamics, structure and evolution. An exploration of Uranus or Neptune will be essential to understand these planets and will also be key to constrain and analyze data obtained at Jupiter, Saturn, and for numerous exoplanets with hydrogen atmospheres.