It is the first time that this important emission has been observed on another planet beyond Earth.
Green glow from Earth’s atmosphere observed from the ISS.
On Earth, bright oxygen is produced during the polar auroras, when the energetic electrons from interplanetary space hit the upper atmosphere. This oxygen-powered light emission gives the polar auroras their beautiful and characteristic greenish hue.
Aurora, however, is just one of the ways in which planetary atmospheres light up. For example, those on Earth and Mars constantly shine during the day and night as sunlight interacts with atoms and molecules within the atmosphere.
The daytime and nighttime glow are caused by slightly different mechanisms: the nighttime glow occurs when broken molecules recombine, while the daylight glow arises when sunlight directly stimulates atoms and molecules such as nitrogen and oxygen.
On Earth, the green night glow is quite subdued, making it best viewed from an “edge” perspective, as shown in many spectacular images taken by astronauts aboard the International Space Station (ISS). This fact can be a problem when looking for it around other planets, since its shiny surfaces can drown it.
Now, this green glow has been detected for the first time on Mars by the Trace Gas Orbiter (TGO) from the ExoMars mission, which has been orbiting Mars since October 2016.
“One of the brightest emissions observed on Earth comes from the night glow. More specifically, from oxygen atoms emitting a particular wavelength of light that has never been seen around another planet,” says Jean-Claude Gérard, from the University of Liege, Belgium, and lead author of the new study published in Nature Astronomy.” However, it had been theorized that this emission had existed on Mars for about 40 years, and, thanks to TGO, we have found it.”
Observation and model of green atmospheric emission on Mars.
Jean-Claude and his colleagues were able to detect this emission using a special TGO observation mode. One of the orbiter’s advanced instrument sets, known as NOMAD (Nadir and Concealment for the Discovery of Mars) and which includes the Ultraviolet and Visible Spectrometer (UVIS), you can observe in various configurations, one of which places your instruments to point directly towards the Martian surface – also known as the “nadir canal”.
“Previous observations had not captured any kind of green glow on Mars, so we decided to reorient the nadir UVIS channel to target the “edge” of Mars, similar to the perspective seen in images of Earth taken from the ISS“ added co-author Ann Carine Vandaele of the Institut Royal d’Aéronomie Spatiale de Belgique and principal investigator of NOMAD.
Between April 24 and December 1, 2019, Jean-Claude, Ann Carine, and their colleagues used NOMAD-UVIS to scan altitudes ranging from 20 to 400 kilometers from the Martian surface twice per orbit. When they analyzed these data sets, they found the green oxygen emission in all of them.
“The emission was strongest at an altitude of around 80 kilometers and varied depending on the changing distance between Mars and the Sun,” adds Vandaele.
Artist rendering of the TGO detecting the green glow of oxygen in the Martian atmosphere. Credit: ESA.
Studying the glare of planetary atmospheres can provide a wealth of information about the composition and dynamics of an atmosphere, and reveal how energy is deposited by both sunlight and the solar wind, the stream of charged particles that emanate of our star.
To better understand this green glow on Mars and compare it to what we see around our own planet, Jean-Claude and his colleagues delved into how it formed.
“We model this emission and discover that it is produced mainly as carbon dioxide, or CO2, and is divided into its constituent parts: carbon monoxide and oxygen,” says Jean-Claude. “We saw the resulting oxygen atoms glowing in both visible and ultraviolet light.”
Simultaneous comparison of these two types of emission showed that the visible emission was 16.5 times more intense than the ultraviolet.
“The observations on Mars are consistent with previous theoretical models, but not with the actual brightness we have seen around Earth, where the visible emission is much weaker,” adds Jean-Claude. “This suggests that we have more to learn about how oxygen atoms behave, which is very important to our understanding of atomic and quantum physics.”
This understanding is key to characterizing planetary atmospheres and related phenomena, such as auroras. By deciphering the structure and behavior of this bright green layer of Mars’ atmosphere, scientists can gain insight into an altitude range that has remained largely unexplored, and control how it changes as the activity of the Sun and Mars varies. it travels along its orbit around our star.
Source: THAT
