Emissions from the upper-atmospheric trihydrogen cation (H3+) have been used to study the global-scale interactions of Jupiter, Saturn and Uranus with their surrounding space environments for over 30 years, revealing the processes shaping the aurorae. However, despite repeated attempts, and contrary to models that predict it should be present, this ion has proven elusive at Neptune. Now, using observations from the NASA/ESA/CSA James Webb Space Telescope,...
