The phenomenon of airglow, the nocturnal glows that sometimes illuminate the sky, is well-known on Earth. However, it is now observed on Mars for the first time in a range of wavelengths that would have made it visible to potential explorers of the Red Planet.
Strange glows have been observed in the Martian sky before, mainly in the ultraviolet range, undetectable by the human eye. This latest observation by scientists at the University of Liège reveals that the light was indeed emitted in the visible range.
Different From Polar Auroras
The Uvis-Nomad instrument, typically dedicated to mapping the ozone layer surrounding the planet, aboard the Trace Gas Orbiter, incidentally detected these unusual glows in the Martian night. Observed between 40 and 70 kilometers altitude, these glows are believed to result from the recombination of oxygen atoms created in the warm atmosphere of Martian summer and transported by winds to the polar regions of the opposite hemisphere during winter. In this region, oxygen atoms, excited by ultraviolet radiation from the Sun, come into contact with CO2 molecules, producing O2 molecules. This molecular recombination emits light in the visible spectral range, a phenomenon known as chemiluminescence, distinct from the one responsible for polar auroras.
Understanding Mars’ Atmospheric Dynamics
While airglow is a familiar phenomenon on Earth and has been observed on Venus, this is the first time it’s been documented on Mars. Researchers have also noted other light emissions in the ultraviolet range, associated with the recombination of oxygen and nitrogen atoms to form nitric oxide (NO). Studying these phenomena could provide insights into the dynamics of the Martian upper atmosphere and its variations throughout the Martian year. These findings have been published in the journal Nature Astronomy.