Eric Chassefière
Biography & lecture abstracts
 |
Lecture Atmosphere-1: Atmospheric structure and dynamics
Although Mars is twice smaller and 50% farther from the Sun than the Earth, its climate has important similarities, such as the polar ice caps, seasonal changes and the observable presence of weather patterns. Although the martian climate has similarities to the Earth's, including seasons and periodic ice ages, there are also important differences such as the absence of liquid water (although frozen water exists) and much lower thermal inertia. The vertical structure of the atmosphere and its space and time variability will be presented. The three main cycles controlling the meteorology and climate of Mars (H2O,CO2, dust), and their interactions with each other, will be described. The way heat is transported in the atmosphere of Mars, and the resulting dynamical regime of the atmosphere, will be explained with reference to the Earth's case. The important question of the long-term climate evolution of Mars will be assessed. The talk will be illustrated by several examples of observations recently made from the martian orbit by Mars Express and other missions.
Lecture Atmosphere-2: Atmospheric chemistry and cycles
Mars has a very thin atmosphere, with a surface pressure of only 7 mbar, made mostly of carbon dioxide. Measurements made thirty years ago by the Viking landers established the exact composition of the atmosphere on Mars as 95.3% carbon dioxide, 2.7% nitrogen and 1.6% argon, with smaller amounts of oxygen (0.15%) and water vapour (0.03%). Because the thin atmosphere is much more transparent than Earth's atmosphere to the solar-ultraviolet light, it is submitted to an intense photochemical activity. The main cycles controlling Mars atmosphere photochemistry will be described, with a particular emphasis on the Chapman cycle involving molecular oxygen and ozone. The longstanding question of the photochemical stability of CO2 will be assessed. The puzzling discovery of methane in the martian atmosphere, with an apparent methane lifetime (3 months) much smaller than its expected photochemical lifetime (300 years), will be presented and discussed. The potential role of strong atmospheric oxidants, like H2O2, in oxidizing methane will be detailed.
Lecture Atmosphere-3: Climates of Mars and Venus
Of all our planetary neighbours, Venus should be the most Earth-like: its size, bulk composition and distance from the Sun are very similar to those of the Earth. Its original atmospheric inventory was probably similar to that of early Earth, with large abundances of carbon dioxide and water. Venus experienced runaway greenhouse warming, which led to its current hostile climate, with a massive CO2 atmosphere (one hundred bar) and a surface temperature of nearly 500°C. On the contrary, Mars is a small and cold planet, with a tenuous CO2 atmosphere (a few millibar) and an average surface temperature of -50°C. Like the Earth and Venus, Mars is thought to have been endowed with large amounts of volatiles but, due to its small size, most of the initial volatile content could have been lost by escape to space. The reasons for the divergent evolutions of Mars and Venus, which didn't allowed these planets to maintain conditions favourable to life, will be presented and discussed.
Lecture Atmosphere-4: Methane on Mars
The recent detection of CH4 in the martian atmosphere suggests that, either a subsurface hydrothermal activity has been at work relatively recently, or some biogenic sources could still be active or have been active in the past. First, the existing data and their uncertainties will be presented and discussed. Some clues to the existence of clathrate-hydrates of methane in the subsurface, and possibly in the atmosphere, storing methane under solid form will be proposed. The consequences for our understanding of the martian carbon cycle of a continuous release of methane over geological times, at a rate similar to the present one, will be assessed. Typical scenarios of the evolution of the main volatile species in the martian atmosphere (H2O, CO2), combining different possible sources (volcanism, hydrothermalism) and sinks (atmospheric escape, carbonate precipitation, crust serpentinization) will be described and discussed. The possibility of a biological origin will be briefly assessed.