Mars reveals its nocturnal secret: discovering its magical green glow

This image shows an artist’s impression of what an astronaut’s nightglow might look like in the polar winter regions of Mars at night. The green glow occurs when oxygen atoms in the atmosphere combine to form oxygen molecules.
This simulated view was created using a real but dark image of the Martian surface from the panoramic camera of NASA’s Opportunity rover, and an artificial nightglow that matches the real color of the oxygen emission. Image source: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.- E.W. Knutsen

ESA’s ExoMars Trace Gas Orbiter has detected a green nightglow in the Martian atmosphere, providing important data on atmospheric processes and potential illumination for future Mars missions. This phenomenon, which is different from the aurora borealis, represents a major advance in our understanding of natural phenomena Mars.

When future astronauts explore Mars’ polar regions, they will see a green glow lighting up the night sky. For the first time, a visible nightglow has been detected in the Martian atmosphere by the European Space Agency’s ExoMars Trace Gas Orbiter (TGO) mission.

Under a clear sky, the glow can be bright enough for humans to see and for rovers to navigate on dark nights. The night glow on Earth is also observed. On Mars, this was expected, but has never been observed in visible light until now.

Night light on Mars

Atmospheric nightglow occurs when two oxygen atoms combine to form an oxygen molecule, about 50 kilometers (~30 miles) above the planet’s surface.

Oxygen atoms have been on a journey: They form on the dayside of Mars when sunlight gives energy to carbon dioxide molecules, causing them to split into pieces. When the oxygen atoms migrate to the night side and stop exciting the Sun, they regroup and emit light at lower altitudes.

This animation depicts the process thought to be responsible for Mars’ night glow. When exposed to solar ultraviolet radiation above an altitude of 70 km, carbon dioxide molecules – the main component of the Martian atmosphere – split into carbon monoxide and oxygen atoms. These oxygen atoms (depicted as red balls) are transported by the Hadley giant cell, which has an ascending branch over the day pole and a descending branch over the winter pole, located in the night hemisphere. Oxygen atoms recombine to form molecular oxygen in the descending branch of the Hadley cell, at an altitude of 30-50 km, and emit infrared radiation. Credit: European Space Agency

“This emission results from the recombination of oxygen atoms that were formed in the summer atmosphere and transported by winds to high winter latitudes, at altitudes ranging from 40 to 60 kilometers in the Martian atmosphere,” explains Laurieann Soret, a researcher from the Atmospheric and Planetary Laboratory. Physics from the University of Liège in Belgium, and part of the team that published the discovery in Nature astronomy.

The illumination from a nightglow can be bright enough to light the way ahead, and see the glow as bright as moonlit clouds on Earth.

“These observations are unexpected and interesting for future missions to the Red Planet,” says Jean-Claude Girard, lead author of the new study and a planetary scientist at the University of Liège.

Airglow occurs in Earth’s atmosphere when sunlight interacts with atoms and molecules in the atmosphere. In this image, taken by astronauts aboard the International Space Station (ISS) in 2011, a green band of oxygen glow appears above the Earth’s curve. On the surface, parts of North Africa appear, where evening lights shine along the Nile River and its delta. Credit: NASA

Follow the glowing green path

It aroused the interest of the international scientific team A Previous discovery They were made using Mars Express, which observed nightglow at infrared wavelengths a decade ago. The Trace Gas Orbiter spacecraft went on to detect glowing green oxygen atoms above Mars’ dayside in 2020, the first time such dayglow emission has been seen around a planet other than Earth.

These atoms also travel to the night side and then reassemble at a lower altitude, creating the visible night glow discovered in new research published today.

Artist’s impression of the European Space Agency Exomars Track the gas orbit Detecting the green glow of oxygen in the Martian atmosphere. This emission, observed on Mars’ dayside, is similar to the nightglow seen around Earth’s atmosphere from space. Credit: European Space Agency

Orbiting the Red Planet at an altitude of 400 kilometers, TGO was able to observe the night side of Mars through its vehicle’s ultraviolet-visible channel. Nomad tool. The instrument covers a spectral range from near ultraviolet to red light, and was pointed toward the edge of the red planet to better observe the upper atmosphere.

The NOMAD experiment is led by the Royal Belgian Institute for Astronautics, and works with teams from Spain (IAA-CSIC), Italy (INAF-IAPS), and the United Kingdom (Open University), among others.

Scientific value

The night glow serves as a tracer of atmospheric processes. It can provide a wealth of information about the composition and dynamics of a region of the atmosphere that is difficult to measure, as well as oxygen density. It can also reveal how energy is deposited by sunlight and the solar wind – the stream of charged particles emanating from our star.

A shot from space of the Milky Way and Earth together outside the International Space Station. The Milky Way Galaxy extends below the curve of Earth’s limb in the scene, which also registers a faint green airglow. The galaxy’s central bulge appears with star fields cut by dark slits of interstellar dust. The photo was taken by NASA astronaut Scott Kelly in 2015 during his one-year mission in space. Image credit: NASA/Scott Kelly

Understanding the properties of the Martian atmosphere is not only scientifically interesting, but also essential for missions to the Red Planet’s surface. For example, the density of the atmosphere directly affects the drag experienced by satellites orbiting Mars and the parachutes used to deliver probes to the Martian surface.

Night glow vs aurora

Nightglow is also observed on Earth, but should not be confused with the aurora borealis. The aurora borealis is just one way the planetary atmosphere is illuminated.

The aurora borealis is produced, On Mars As on Earth, when energetic electrons from the Sun hit the upper atmosphere. They vary across space and time, while night light is more uniform. Both nightglow and aurora borealis can show 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, so it is best seen by looking from an “edge” perspective – as shown in Many amazing photos Taken by astronauts International Space Station.

Time lapse video by European Space Agency The photo was taken of astronaut Tim Peake during his six-month Principia mission on the International Space Station. The British astronaut commented on this timelapse: “ISS view of the ‘aurora rising’ – do you see the two satellites at the end? A Timelapse video created from images taken at one-second intervals played 25 times faster. Credit: European Space Agency/NASA

Reference: “Mars Observation O₂ “Night Glow Visible by the NOMAD Spectrograph on Board the Trace Gas Orbiter” by J.-C. Girard, L. Surette, I.R. Thomas, P. Ristic, Y. Willam, C. Debez, A.C. Vandel, F. Dearden, B. Hubert, J.P. Mason, M.R. Patel, and M.A. Lopez Valverde, November 9, 2023, Nature astronomy.
doi: 10.1038/s41550-023-02104-8