New analysis of data sent back by the SPICAM spectrometer on board ESA’s Mars Express spacecraft has revealed for the first time that the planet’s atmosphere is supersaturated with water vapour. This surprising discovery has major implications for understanding the Martian water cycle and the historical evolution of the atmosphere.
… Until now, it was generally assumed that such supersaturation cannot exist in the cold Martian atmosphere: any water vapour in excess of saturation was expected to be converted immediately into ice. However, the SPICAM data have revealed that supersaturation occurs frequently in the middle atmosphere — at altitudes of up to 50 km above the surface — during the aphelion season, the period when Mars is near its farthest point from the Sun.
Extremely high levels of supersaturation were found on Mars, up to 10 times greater than those found on Earth. Clearly, there is much more water vapour in the upper Martian atmosphere than anyone ever imagined. It seems that previous models have greatly underestimated the quantities of water vapour at heights of 20–50 km, with as much as 10 to 100 times more water than expected at this altitude.
“The vertical distribution of water vapour is a key factor in the study of Mars’ hydrological cycle, and the old paradigm that it is mainly controlled by saturation physics now needs to be revised,” said Luca Maltagliati. “Our finding has major implications for understanding the planet’s global climate and the transport of water from one hemisphere to the other.”
“The data suggest that much more water vapour is being carried high enough in the atmosphere to be affected by photodissociation,” added Franck Montmessin, also from LATMOS, who is the Principal Investigator for SPICAM and a co-author of the paper.
“Solar radiation can split the water molecules into oxygen and hydrogen atoms, which can then escape into space. This has implications for the rate at which water has been lost from the planet and for the long-term evolution of the Martian surface and atmosphere.” …