Title of thesis
Spectro-photometric properties of Phobos and Deimos surfaces : preparation of the Martian Moons eXploration mission
Composition of the jury
- Pierre Vernazza (Université Aix-Marseille, LAM) - Reporter
- Olivier Groussin (Université Aix-Marseille, LAM) - Reporter
- François Forget (Sorbonne Université, LMD) - Examiner
- Eri Tatsumi (Instituto de Astrofisica de Canarias) - Examiner
- Cecile Engrand (Université Paris-Saclay, IJCLab) - Examiner
- Abigail Fraeman (NASA, JPL) - Examiner
- Thomas Gautier (LATMOS) - Thesis supervisor
- Alain Doressoundiram (Observatoire de Paris, LIRA) - Thesis supervisor
Abstract
The two Martian moons, Phobos and Deimos, have benefited of a lot of observations since the 1970s. However, despite this development, the origins of the two moons remain uncertain, with two main hypotheses being discussed. The first one is the giant impact hypothesis, which suggests that an impactor collided with Mars in its early history, creating a debris disk that subsequently accreted into Phobos and Deimos. The second theory is based on the capture of one or two asteroids from the outer Main Belt or the Jupiter Trojans swarm, as revealed by their spectroscopic properties. The question of the origin of Phobos and Deimos will be resolved by the Martian Moon eXploration (MMX) mission of the Japanese space agency, which is scheduled to be launched in 2026 and is equipped with a suite of remote-sensing instruments. Notably, the MIRS infrared spectrometer will allow the detection of minerals and organic compounds on the surface of the Martian moons, and MMX will return samples from Phobos to Earth in 2031 which will likely provide definitive conclusions. This work is carried out as part of the MMX mission, and in particular in preparation for future MIRS observations. More specifically, the objective is to provide more detailed constraints on the surface composition and texture of the Martian moons.
This thesis is divided into two main parts. Firstly, a photometric and spectroscopic analysis of the surface of the Martian moons was conducted using available data from ground-based observations, as well as remote-sensing observations of the HRSC camera onboard Mars Express. Secondly, laboratory experiments and simulations of MMX/MIRS observations were performed to prepare the interpretation of the data and to provide additional constraints on the surface properties. My analysis of the HRSC and ground-based data reinforced the hypothesis that Phobos and Deimos have a common origin. Additionally, we found that the blue unit on Phobos is up to 50% brighter than the average surface, with the grooves at the northeastern rim of the Stickney crater being the brightest features on Phobos. A similar analysis of Deimos revealed the presence of a blue unit, characterised by a brighter (30%) and slightly less red visible and near-infrared spectrum. The laboratory experiments demonstrated that the spectroscopic variations associated with the blue unit may be attributable to a porous regolith layer, rather than only to fresher, non-altered materials, as is generally hypothesized. A detailed analysis of the blue and red units present on both Phobos and Deimos has the potential to reveal the origin of the Martian moons. My results suggest that D-type-like materials exhibit a blueing effect following ion irradiation, while basaltic Martian materials are likely to redden. The presence of significant differences of alteration markers by space-weathering between these two units could provide clear evidence for the distinction between the red and blue units. In this case, the origin of the Martian moons would be linked with Martian materials, most likely resulting from a giant impact. In this case, the origin of the Martian moons would be associated with Martian material, most likely from a giant impact. Conversely, the presence of certain compounds, such as organic matter or water ice, would clearly indicate an origin linked to the capture of a primitive asteroid, hypothetically from a single Z-type object coming from the inner main belt that was disrupted during capture, forming Phobos and Deimos.
