ESA Mars Express: Seasonal Ozone Layer Over The Martian South Pole

Ozone production over Mars southern winter pole.
Credit: ESA/ATG medialab.

For the past decade, ESA's Mars Express orbiter has been observing atmospheric structure on the Red Planet.

Among its discoveries is the presence of three separate ozone layers, each with its own characteristics.

A new comparison of spacecraft data with computer models explains how global atmospheric circulation creates a layer of ozone above the planet's southern winter pole.

Ozone (O3) is a form of oxygen gas which contains three atoms, rather than two.

On Earth, ozone is a pollutant at ground level, but at higher altitudes it provides an essential protective layer against harmful solar ultraviolet (UV) light.

However, ozone molecules are easily destroyed by solar ultraviolet light and by chemical reactions with hydrogen radicals, which are released by photolysis (splitting) of water molecules.

The role of pollution in its destruction has been a major focus of attention since the mid-1980s, when a hole in the ozone layer was discovered above Antarctica.

Until the early 1970s, no one could be sure whether ozone existed on any of the other planets. Ozone was then detected on Mars and it has since been discovered on Venus by ESA's Venus Express mission.

ESA's Mars Express orbiter

On Mars, the ozone concentration is typically 300 times thinner than on Earth, although it varies greatly with location and time.

In recent years, the SPICAM UV spectrometer on board Mars Express has shown the presence of two distinct ozone layers at low-to-mid latitudes.

These comprise a persistent, near-surface layer below an altitude of 30 km, and a separate layer, which is only present in northern spring and summer, and whose altitude varies from 30 to 60 km.

In recent years, SPICAM has also provided evidence for the existence of a third ozone layer which exists 40-60 km above the southern winter pole, with no counterpart above the North Pole.

In a paper published in the journal Nature Geoscience, Franck Montmessin and Franck Lefevre, two scientists from LATMOS in Guyancourt, France, have analysed approximately 3000 occultation sequences and vertical ozone profiles collected by SPICAM on the night side of Mars.