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This image shows an artist’s impression of what nighttime glow would look like for an astronaut in the winter polar regions of Mars at night. The green glow occurs when oxygen atoms high in the atmosphere combine to form oxygen molecules.
This simulated view was created using a real but darkened image of the Martian surface taken by the panoramic camera on NASA’s Opportunity rover, and a synthetic night glow corresponding to the real color of the oxygen emission. Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.– EW Knutsen
ESA’s ExoMars Trace Gas Orbiter has discovered a green nighttime glow in the Martian atmosphere, providing crucial data on atmospheric processes and potential lighting for future Martian missions. This phenomenon, distinct from auroras, marks a significant advance in our understanding of the When future astronauts explore the polar regions of Mars, they will see a green glow lighting up the night sky. For the first time, a visible night glow has been detected in the Martian atmosphere by ESA’s ExoMars Trace Gas Orbiter (TGO) mission.
Under clear skies, the glow could be strong enough for humans to see and for rovers to navigate on dark nights. Nightglow is also observed on Earth. On Mars, it was expected but never observed in visible light until now.
Nightglow on Mars
Atmospheric nightglow occurs when two oxygen atoms combine to form an oxygen molecule, about 50 km (~30 miles) above the planetary surface.
Oxygen atoms are on a journey: they form on the dayside of Mars, when sunlight provides energy to carbon dioxide molecules, causing them to split apart. When oxygen atoms migrate to the night side and stop being excited by the Sun, they regroup and emit light at lower altitudes.
This animation shows the process believed to be responsible for the Martian night glow. When exposed to ultraviolet solar radiation above an altitude of 70 km, carbon dioxide molecules – the main atmospheric constituent of Mars’ atmosphere – are split into carbon monoxide and oxygen atoms. These oxygen atoms (represented as red spheres) are transported by a gigantic Hadley cell, which has an ascending branch above the daytime summer pole and a descending branch over the winter pole, which is in the nighttime hemisphere. Oxygen atoms recombine into molecular oxygen in the descending branch of the Hadley cell at an altitude of 30-50 km, emitting infrared radiation. Credit: ESA
“This emission is due to the recombination of oxygen atoms created in the summer atmosphere and transported by winds to high winter latitudes, at altitudes of 40 to 60 km in the Martian atmosphere”, explains Lauriane Soret, researcher at the Atmospheric and Planetary Analysis Laboratory. . Physics at the University of Liège, Belgium, and part of the team that published the discovery in Nature Astronomy.
Night glow lighting can be bright enough to illuminate the path of the future and see the glow as bright as the moonlit clouds on Earth.
“These observations are unexpected and interesting for future trips to the Red Planet,” says Jean-Claude Gérard, lead author of the new study and planetary scientist at the University of Liège.
Airglow occurs in Earth’s atmospheres as sunlight interacts with atoms and molecules within the atmosphere. In this image, taken by astronauts aboard the International Space Station (ISS) in 2011, a green band of oxygen glow is visible over the curve of the Earth. On the surface, portions of North Africa are visible, with night lights shining along the Nile River and its delta. Credit: NASA
Follow the bright green road
The international science team was intrigued by a previous discovery made using Mars Express, which observed night glow in infrared wavelengths a decade ago. The Trace Gas Orbiter detected glowing green oxygen atoms high above the dayside of Mars in 2020 – the first time this dayglow emission has been seen around a planet other than Earth.
These atoms also travel to the night side and then recombine at lower altitudes, resulting in the visible night glow detected in new research published today.
Artist’s impression of ESA’s ExoMars Trace Gas Orbiter detecting the green glow of oxygen in the Martian atmosphere. This emission, detected on the dayside of Mars, is similar to the nighttime glow seen from space around Earth’s atmosphere. Credit: ESA
Orbiting the Red Planet at an altitude of 400 km, TGO was able to monitor the night side of Mars with the ultraviolet-visible channel of its NOMAD instrument. The instrument covers a spectral range from near-ultraviolet to red light and has been oriented toward the edge of the Red Planet to better observe the upper atmosphere.
The NOMAD experience is led by the Royal Belgian Institute of Space Aeronomy, working with teams from Spain (IAA-CSIC), Italy (INAF-IAPS) and the United Kingdom (Open University), among others.
Scientific Value
Night glow serves as a tracker of atmospheric processes. It can provide a lot of information about the composition and dynamics of a difficult-to-measure region of the atmosphere, as well as the oxygen density. It could also reveal how energy is deposited by both sunlight and the solar wind – the stream of charged particles emanating from our star.
Space snapshot of the Milky Way and Earth posing together beyond the International Space Station. The Milky Way extends below the curve of Earth’s limb in the scene that also records a faint green glow from the air. The central bulge of the galaxy appears with star fields cut by dark rifts of obscure interstellar dust. The photo was taken by NASA astronaut Scott Kelly in 2015 during his year-long mission in space. Credit: NASA/Scott Kelly
Understanding the properties of Mars’ atmosphere is not only scientifically interesting, but also critical for missions to the surface of the Red Planet. Atmospheric density, for example, directly affects the drag experienced by orbiting satellites and the parachutes used to launch probes to the Martian surface.
Night glow versus aurora
Nightglow is also observed on Earth, but should not be confused with auroras. Auroras are just one way in which planetary atmospheres light up.
Auroras are produced, both on Mars and Earth, when energetic electrons from the Sun reach the upper atmosphere. They vary in space and time, while nighttime brightness is more homogeneous. Night glow and auroras can display a wide range of colors depending on which atmospheric gases are most abundant at different altitudes.
The green night glow on our planet is quite faint and is therefore best observed from an “sideways” perspective – as depicted in many spectacular images taken by astronauts from the
A timelapse video of
