Mars’ Water Cycle and Escape: A View from Mars Express and Beyond
摘要
The search for water on Mars has long been a theme of intense exploration, as it represents a means of addressing Mars’ current climate as well as its evolution in the recent and more distant past. Since the 1970s, several missions have carried instruments to track water in the atmosphere, leading to the conceptualization of a water cycle on Mars characterized by intense seasonal variability in water vapor abundance across the planet. After Mariner 9, Viking, Phobos 2 and Mars Global Surveyor, Mars Express has become the fifth orbiter capable of detecting water vapour, with unique features: measurements by several instruments, each probing a distinct wavelength region from near-infrared to thermal infrared, altitude-dependent profiling of water thanks to solar occultation, and observation in the exosphere of its by-product, hydrogen atoms, which can escape into space, depriving Mars of its primordial water reservoir. Thanks to Mars Express, a new vision of Mars’ water cycle and escape processes has emerged. The achievements of Mars Express, as well as the legacy of other missions, which established the foundations of our understanding of Mars’ water cycle are presented in this article.