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A strange green halo on the martian surface. That is what has captured the Satellite for the study of Trace Gases ( TGO ) of the mission ExoMars of the European Space Agency (ESA), who has been orbiting Mars from 2016 to learn more about the atmosphere of our neighbor. This is the first time it is detected on a planet different from Earth, so that means a milestone of spatial relevance.

“One of the emissions the brightest seen on Earth comes from the night glow. More specifically, atoms of oxygen, and emit a wavelength particular light that has never been around another planet, Jean-Claude Gérard , University of Liege, Belgium, and lead author of the new study published in Nature Astronomy. “However, it is anticipated that this issue exists on Mars for about 40 years, and, thanks to TGO, we found”, explains in a press release.

The mechanism in the Earth

On Earth, the oxygen glows during the aurora, when the charged electrons from the interplanetary space, collide with the upper atmosphere . The light emission due to the oxygen gives the aurora its characteristic greenish shade. However, the aurora is not only one of the ways in which the planetary atmospheres shine. In the case of planets like Earth and Mars , the luminescence is constant during the day and night while the solar light interacts with atoms and molecules of the atmosphere. Glows day and night are due to mechanisms something different: the night will occur when recombined molecules decomposed, while the day arise when the Sunlight directly drives atoms and molecules such as nitrogen and oxygen.

On Earth, the night glow green is very dim, so it is best to see way cross, as shown by numerous spectacular images taken by astronauts aboard the International Space Station (ISS). The weakness of the glare can be a problem when looking around other planets, since the brightness of the surface can put the lid back on.

How you could see the halo on Mars

Gérard and his colleagues were able to detect this emission on Mars using a mode special observation of the TGO . One of the sets of advanced instruments of the orbiter, known as the NOMAD (Nadir and Occultation for the discovery of Mars) and including the spectrometer, ultraviolet and visible (UVIS), can be observed in several configurations, one of which placed their instruments directly pointing towards the martian. surface – also known as the channel ‘nadir’.

“previous observations had not captured any kind of green glow on Mars, so we decided to refocus the channel nadir UVIS to point to the ‘edge’ of Mars, similar to the perspective that is seen in the images of the Earth taken from the ISS,” adds co-author Ann Carine Vandaele of the Institut Royal d Aéronomie Spatiale de Belgique, Belgium, and principal investigator of NOMAD.

Studying other radiances

The study of the glow of planetary atmospheres can offer a lot of information about the composition and the dynamics of the atmosphere , and to reveal how it is deposited to the energy of the sunlight and the solar wind, the stream of charged particles from our star.

Understanding the properties of the martian atmosphere not only has a scientific interest, it is also critical to operate the missions that are sent to the medium-term to the Red Planet. Atmospheric density, for example, directly affects the drag experienced by satellites in orbit and by the parachutes used to pose probes on the martian surface.