It is not only on earth that the sky shines at night. For the first time, ESA’s Trace Gas Orbiter (TGO) probe has captured the phenomenonairglow, or sky glow in French, around the planet Mars. An observation that could lead to new discoveries about the atmosphere of the Red Planet, with possible consequences for its exploration.
This airglow is exactly what the title suggests: under certain conditions, atoms in the upper atmosphere emit a diffuse light that illuminates the night sky. It’s because of this airglow that the Earth’s sky is never completely black, even if we ignore the light of the Sun traveling from the other side of the Earth.
All mechanisms that generate this glow are not yet fully understood. It is for this reason that researchers recently created a airglow artificially in Alaska, to study the mechanism in depth.
Why researchers light up Alaska’s skies
An elusive glow
During the day, the sun’s radiation excites carbon dioxide molecules in Mars’ atmosphere, causing them to break apart. This is how we obtain carbon and oxygen atoms. This separation produces a slight glow that was first observed in 2020.
On the other hand, this radiation occurs at high altitudes (about 150 km) and only affects the illuminated part of Mars. It is therefore of little interest to researchers studying the dynamics of Mars’ atmosphere. To obtain more interesting information, we should work on a similar glow at a lower altitude, about 50 km altitude.
The Mars Express probe had already observed such radiation in the infrared region about ten years ago. But until recently there was no evidence of this airglow Martian also ventured into the visible domain.
An intermediary for studying the atmosphere
This has changed thanks to NOMAD, the Trace Gas Orbiter’s UV-visible sensor. Finally the ESA was able to do this observe a airglow for the first time at night in the visible domain.
The origin of this other glow is slightly different. She is closely associated with oxygen atoms due to the decomposition of CO2 mentioned above. These atoms migrate with the wind through the atmosphere until they reach the unlit side of the planet. When placed in the shade, the oxygen atoms tend to combine in contact with CO2 to form an atom dioxygen molecule in an excited state. This excess energy is then released, which is reflected in the production of light.
This discovery may seem anecdotal, but it could have significant implications for planetary scientists. This skyglow can indeed serve as an intermediary in studying various chemical and physical processes. Because of this airglow visible, researchers will be able to do so study the composition and dynamics of Mars’ atmosphere in a region where current machines traditionally struggle to make accurate measurements.
“ The study of these emissions is an excellent tool for studying the composition and dynamics of the Martian atmosphere between 40 and 80 km », explains Benoit Hubert, researcher at the University of Liège.
A resource for future Mars missions
In addition to the challenges in fundamental science, these measurements can also directly contribute to the success of future missions on Mars. “ These new observations are unexpected and very interesting for future trips to the Red Planet », rejoices Jean-Claude Gérard, researcher at the University of Liège and lead author of this work.
For example, airglow can be used locally estimates the density of the atmosphere. This is very important data for the various devices used in Mars exploration.
First of all, her directly affects the trajectory of vehicles placed in orbit. The higher it is, the more friction the satellites have to endure. In the long term, it is therefore essential to take this into account to adequately correct their trajectory so that they do not dive to the surface prematurely.
Rovers and other surface equipment can also benefit from this information. Mars’ atmosphere may be much less dense than Earth’s, but it is still enough to allow spacecraft to land parachutes. However, their ability to slow the fall of objects depends directly on the density of the atmosphere. So studying the skyglow could help engineers refine the deployment of the next reconnaissance vehicles.
All that remains is to study this airglow closer. And the good news is that, according to the study authors, it will be quite easy to achieve this. “ The intensity of this glow from the night sky is such that relatively simple and inexpensive instruments can use it to study atmospheric currents. A future ESA mission could easily carry a camera to capture this on a global scale », concludes Gérard.
The text of the study can be found here.