The mystery of the blue light strip on Mars

The European Space Agency (ESA) first observed the green band around a planet other than Earth.

The atmosphere of planets like Earth and Mars glow continuously day and night due to sunlight interacting with atoms and molecules neutral in the atmosphere. The glow at two opposites during the day is caused by two different mechanisms. While blue light at night comes from the combined molecules, the daytime glow is caused by the Sun's direct stimulation of atoms and molecules such as nitrogen and oxygen.

Graphic that simulates the orbital ExoMars and the blue light strip on Mars atmosphere. (Photo: ESA).

On Earth, the phenomenon appears rather faint and is most clearly observed in low-level orbit, such as from the position of the International Space Station (ISS). On other planets, it is difficult to hunt down the faint blue band because they are overwhelmed by the bright surface of the celestial body.

"The blue band around the Earth is best seen at night. At that time, the oxygen atoms in the atmosphere emit a special wavelength of light ," said lead author Jean-Claude Gérard from Belgium's de Liège University said. " This glow is also predicted to exist on Mars 40 years ago but until now we have found it thanks to the orbit ExoMars."

Jean-Claude and his colleagues used the Ultraviolet and Visible Spectroscopy (UVIS), one of ExoMars' most advanced tools, to study the atmosphere of the "red planet" in the regime. Special observations from April to December last year.

Blue bands in the Earth's atmosphere seen from the ISS. (Photo: NASA).

"Previous direct observations didn't capture any blue light, so we decided to adjust the UVIS towards the edge of Mars, just like how astronauts photograph phenomena from ISS , " co-author of the study Ann Carine Vandaele from Belgium's Royalutéomomie Spatiale de Belgique Institute adds.

The team scanned the Martian atmosphere at altitudes between 20 and 400km and detected blue light at all altitudes; in particular, the band appears most clearly at 80km from the surface.

Based on computer models, the scientists found that the blue light on Mars is mainly derived from the decay of carbon dioxide - accounting for 95% of the planet's atmosphere - into carbon monixide and oxygen. These oxygen atoms glow in both visible and ultraviolet light; of which, visible light is 16.5 times stronger than ultraviolet light.

This new discovery is key to describing planetary atmospheres and related phenomena such as aurora. By deciphering the structure of the blue glowing atmosphere on Mars, astronomers can better understand the unexplored range of altitudes, and track its changes in activity. of the Sun changes and when Mars moves in orbit around the star.