March 26, 2012

A light in the Martian night

French scientists working on Mars Express discovered a new type of night light emissions on the planet Mars. This discovery explains how the Mars' upper atmosphere moves depending on the seasons.

Using the OMEGA spectrometer, they detected a 1.27 µm emission, the control signature of oxygen (O2) when it just formed from the recombination of two oxygen atoms (O + O).

This emission is not permanent. Over the 40 observations of the night side, only three did detect a strong signal, all three located in the polar regions. This is exactly what a sophisticated 3-dimensional model of the Martian atmosphere predicted when simulating both the circulation and the chemistry of the atmosphere.

When the carbon dioxide molecules (CO2), the main component of the Martian atmosphere, are being exposed to UV solar radiations at an altitude of more than 70 km, they break up into carbon monoxide (CO) and oxygen (O) atoms. These oxygen atoms are then horizontally carried within a huge Hadley-type cell which links the upward part of the summer pole (i.e. the North Pole) with the opposite pole on the winter side (i.e. the South Pole) and spreads by night. Then the oxygen (O) atoms recombine into oxygen (O2) atoms along the downward part of the Hadley cell.

Jean-Loup Bertaux, main author of the study, explained: “On Earth, such circulation pattern is also well known: at every solstice, the upstream air in the summer pole manifests itself by beautiful noctilucent ice clouds because water vapour cool down and turn quickly into ice.“ ”The phenomenon alternates every six months.

Nevertheless, on Mars, the OMEGA and model's data show that, at every equinox, a different model is issued with two symmetrical Hadley cells: upstream air close to the equator dividing itself into two parts to the North and South with simultaneous downstream air towards both poles.

Our results on Mars should enhance the research on the Earth's atmosphere, either to detect a similar situation at the equinox, or to understand why does this exist on Mars and not on Earth.“ ”The twice as long Martian seasons could be an explaining factor.”

Article references

First detection of O2 1.27 µm nightglow emission at Mars with OMEGA/MEX and comparison with general circulation model predictions
J. L. Bertaux1 B. Gondet2 F. Lefèvre3 J. P. Bibring2 and F. Montmessin1

1. Laboratoire Atmosphères, Milieux, Observations Spatiales/Institut,Pierre Simon Laplace, Université de Versailles Saint-Quentin/CNRS, Guyancourt, France.
2. Institut d’Astrophysique Spatiale, Université de Paris Sud 11, Orsay, France.
3. Laboratoire Atmosphères, Milieux, Observations Spatiales /Institut Pierre Simon Laplace, Université Pierre et Marie Curie/CNRS, Paris, France.


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