With NOMAD on board ExoMars

Arnaud Stiepen wants to know more about the phenomena he revealed about the atmospheric environment of Mars. He is currently interested in the abundance of data captured by sensors in the UV (ultraviolet). Observations in this spectral waveband are a speciality of the Institute for Astrophysics and Geophysics of Liege. “What interests me is a new type of aurora, different to those discovered on Mars by the ESA’s Mars Express probe in 2005. These are diffuse auroras which have been detected on a section of the Red Planet in its Northern hemisphere. What is surprising is that these auroras appear very low in the atmosphere, under the effect of higher energy electrons than is the case during the appearance of discreet auroras”.

While working on the observations made by the MAVEN probe, the astrophysicist from Liege did not expect to have confirmation of so-called “diffuse” auroras. This was one of the first results provided by MAVEN in December 2014 thanks to its IUVS (Imaging UV Spectrograph) instrument. For one year, Arnaud Stiepen was part of the team that examined the data from the ultraviolet imaging spectrograph. He took part in a press conference organised by NASA to speak about the surprises he had uncovered in these “diffuse” auroras which are difficult to detect due to the very faint light coming from them. “This type of aurora is caused by high-energy particles which for this reason are unpredictable. There is no possibility of studying the phenomenon in a routine way: you have to be in the right place at the right time in order to detect and study them”. By means of MAVEN, it is possible to use several instruments to conduct combined observations of this auroral phenomenon. “You need to understand where the electrons that cause the aurora are coming from, how they are accelerated by following the lines of the magnetic field…”


At the heart of the Martian tragedy 

The auroras are not the only focus of Arnaud Stiepen’s interest. Mars has the particularity of having a very thin atmosphere, composed of 95 % carbon dioxide (carbonic gas). 

The observations made by the American probes on Mars show that the atmospheric pressure on Mars 3.5 million years ago was 150 times greater than its current level, a level similar to our own planet… What is the explanation for the slow and inevitable metamorphosis that was produced resulting in the near disappearance of the Martian atmosphere? The MAVEN probe provided new evidence about the dramatic evolution of Mars thanks to the IUVS (Imaging Ultraviolet Spectrograph) developed by the LASP (Laboratory for Atmospheric and Space Physics) of the University of Colorado. This renowned laboratory became interested in the work of Arnaud Stiepen, who studied the atmospheres of Earth’s neighbouring planets Venus and Mars for his doctoral thesis. He drew on his expertise on processing the data transmitted by the IUVS. 

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