Credit: www.esa.int
On June 2nd, 2003, European Space Agency (ESA) launched a probe named Mars Express to investigate, well, Mars. Now, it is orbiting its target at the orbital inclination of 86.3 degree with a period of 6 h 43m. On board, SPICAM spectrometer works by receiving a light from Mars, putting it through grating, and looking for a pattern in a spectrum to determine what does Mars’ atmosphere consist of. From a discovery published in Science by Maltagliati et al (2011), Mars’ atmosphere is supersaturated with water vapor.
Don’t get carried away here. Even though the term for Martian atmosphere is “supersaturated” with water vapor, it is still about 10000 times less water vapor than that of the Earth. But it is “wetter” than we expected anyway (around 10 to 100 times.) At first, scientists thought that the supersaturated state cannot exist on Mars because when the atmosphere is already saturated with water, the excess part would get frozen by Mars’ cold temperature. However, the data from SPICAM suggest that the supersaturated state exists at 50 km above the ground even when Mars is at its farthest point from the Sun.
Similar to that on Earth, energy from Sun’s ray is a part of the Martian water cycle. When ice at the polar caps are warmed up by the sun during spring and summer, it sublimates (not evaporates!) into the atmosphere. It sticks with dust in the air, if there is any, to form a cloud. But when not many dusts exist, water molecules fill the air and turn it into the supersaturated state. At high altitude, wind is so strong that it might blow water molecules to another pole or up even higher. In a high altitude, the Sun attacks water molecules, photodissociation, by breaking it into two hydrogen atoms and an oxygen atom. Those atoms could escape from Mars into a vast universe.
More studies are still needed to fully understand the whole hydrological cycle. For now, we know that Mars continuously lose water but at different rate depending on a season and atmospheric weather.
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