The IUVS instrument observes the atmosphere at different altitudes by sweeping across it following vertical zones in search of markers due to the luminescence and auroras. From the position, intensity and shape of these emissions, it is possible to get an understanding of the dynamic and chemical processes which produced them. The IUVS provides a new view of the impact of solar activity on the atmospheric behaviour of Mars. “What particularly interests me, is to know whether the Martian atmosphere is capable of changing rapidly and how it changes under the effects of the Sun and gravitational waves that are spread across the surface of Mars”. The participation of Arnaud Stiepen in research by the LASP could only be beneficial to the LPAP. So this expert on the atmospheres of Mars and Venus who hails from Liege distinguished himself by contributing to a major discovery on the evolution of the Martian atmosphere: the progressive erosion of this atmosphere over a period of 3 to 4 billion years due to the impact of ions and electrons emitted by the sun.  

“This erosion continues as long as there is an atmosphere”, explains Arnaud Stiepen, “Most of all, we want to understand this slow process by taking a trip back in time. We would like to determine the mass that the Martian atmosphere lost over a period of three to four billion years. In this way, we will be able to extrapolate what the Martian atmosphere will be like in the future”. He also refers to a shift in paradigm in the context of his investigation: “Before we had the information from the MAVEN probe, we thought that the erosion of the Martian atmosphere by the solar wind was somewhat calm. We now know that this was absolutely not the case. We were able to understand the fact that the solar wind wore away the atmosphere over the ages due to its violent eruptions. These energetic solar events are a very important element which must be taken into account in terms of the overall erosion”. 

This phenomenon of erosion cannot be underestimated. As the co-author of a report on the data from MAVEN with regard to this process, Arnaud Stiepen points out: “What we know, is that the atmosphere some three to four billion years ago was denser, warmer and capable of retaining liquid water on its surface. And then, over time – in the order of hundreds of millions of years – this layer became eroded. In this study, I used the airglow value, that is to say the light produced by the excited atmosphere. This gives us information about the composition, dynamics and the atmospheric winds”. If the Sun is shown to be more active and is reheating the atmosphere, we can understand that more of the atmosphere was released into space. The evolution of the Martian atmosphere reveals the action of the solar wind. “It’s a little bit like wind erosion on a mountain”. The major discovery concerns the role of CMEs (Coronal Mass Ejections) or ejections of the coronal mass as accelerators of erosion. The Red Planet sometimes finds itself in the path of this high-energy plasma ejected from the Sun. Because the planet does not have a magnetic field to deflect these ejections, it directly excites the Martian atmosphere and accelerate its erosion. 

Using NOMAD for better results

This behaviour of CMEs is enough to stimulate the curiosity of Arnaud Stiepen. Especially as the LPAP is counting on his productive collaboration with the IASB to make the most of the observations made by NOMAD. “If the objective of the first instrument developed in Belgium is the study of methane in the atmosphere, we can use this for the measurement of other constituents and dynamics processes. I am counting on having access to the data to learn more about my subjects of interest concerning Mars which are the “diffuse” auroras and atmospheric erosion”.