The atmospheric nightglow is observed on Earth. On Mars, it was something expected, yet never observed in visible light until now.
This image shows an artist’s impression of what nightglow might look like to an astronaut in the polar winter regions of Mars at night. Image credit: NASA / JPL-Caltech /Cornell University / Arizona State University / E.W. Knutsen.
Airglow occurs when two oxygen atoms combine to form an oxygen molecule, about 50 km above the planetary surface.
The oxygen atoms form on Mars’s dayside when sunlight gives energy to carbon dioxide molecules, making them split apart.
When the oxygen atoms migrate to the night side and stop being excited by the Sun, they regroup and emit light at lower altitudes.
“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,” said Dr. Lauriane Soret, a planetary scientist at the University of Liège.
The illumination from the nightglow could be bright enough to light the way of future see the glow as bright as moonlit clouds on Earth.
“These observations are unexpected and interesting for future trips to the Red Planet,” said Dr. Jean-Claude Gérard, a planetary scientist at the University of Liège.
ESA’s Mars Express spacecraft observed the Martian nightglow in infrared wavelengths a decade ago.
ESA’s Trace Gas Orbiter followed up by detecting glowing green oxygen atoms high above the dayside of Mars in 2020 — the first time that this dayglow emission was seen around a planet other than Earth.
These atoms also travel to the nightside and then recombine at lower altitude, resulting in the visible nightglow detected by the orbiter.
Orbiting Mars at an altitude of 400 km, Trace Gas Orbiter 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 was oriented towards the edge of the planet to better observe the upper atmosphere.
“The nightglow serves as a tracer of atmospheric processes,” the researchers said.
“It can provide a wealth of information about the composition and dynamics of a region of the atmosphere difficult to measure, as well as the oxygen density.”
“It can also reveal how energy is deposited by both the Sun’s light and the solar wind.”
“Understanding the properties of the Martian atmosphere is not only scientifically interesting but it is also key for missions to the planet’s surface.”
“Atmospheric density, for example, directly affects the drag experienced by orbiting satellites and by the parachutes used to deliver probes to the Martian surface.”
The team’s paper was published in the journal Nature Astronomy.
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JC. Gérard et al. Observation of the Mars O2 visible nightglow by the NOMAD spectrometer onboard the Trace Gas Orbiter. Nat Astron, published online November 9, 2023; doi: 10.1038/s41550-023-02104-8
