Extraordinary phenomena in the sky inspire not only aerial photographers, but also scientists who want to find out the finer details. Researchers in Spain have studied the spectrum of a mesospheric ghost and how it changes over time. Such a ‘ghost’ (Green emissions from excited Oxygen in Sprite Tops, see also the video below at 1:10) is the green glow that sometimes appears above a ‘red sprite’. It was previously thought that this glow was caused by excited atomic oxygen. But after further analysis, it appears to be made up of something else, the researchers report in Nature Communications. Although there was some excited oxygen, there were a number of particles that the researchers believe are responsible for the phenomenon: atomic iron, nickel and nitrogen, molecular nitrogen and ionic molecular oxygen (O₂⁺). They also found traces of sodium and ionic silicon.

Passas-Varo, M. et al. (2023) Nat. Commun. 14(7810), DOI: 10.1038/s41467-023-42892-1