Laboratory investigation of perchlorate deliquescence at the surface of Mars with a Raman scattering lidar

A sample of magnesium perchlorate hexahydrate was subjected to the water vapor pressure and temperatures found at the landing site of the Phoenix Mars mission. Laser Raman scattering was applied to detect the onset of deliquescence and provide a relative estimate of the quantity of water taken up and subsequently released by the sample. As the temperature of the sample decreased at the same rate as measured on Mars during the evening, significant uptake of water from the atmosphere was observed to occur prior to the frost point temperature being reached. As the temperature was lowered further, the relative humidity over ice increased to 100% and frost formed on the surface surrounding the perchlorate sample. Freezing of the brine film was observed at the eutectic temperature of −67°C, and thawing occurred at a temperature of −62°C.