Noctilucent clouds found on Mars
The European Space Agency (ESA) Mars Express spacecraft has found new cloud formations, high in the atmosphere above Mars. While clouds have been seen before on Mars, they have clung to the lower atmosphere. These new discoveries are between 80 and 100 km above the planet's red earth. These new clouds were discovered by accident, thanks to the Mars Express SPICAM ultraviolet and infrared atmospheric spectrometer. The instrument was used to observe stars just above the horizon, as they slipped behind Mars. As the light travels through the Martian atmosphere, it allows the instrument to develop a picture of the Martian atmosphere. In the region around 90 km high, the light dimmed significantly about one per cent of the time. Following some 600 sweeps of the atmosphere, the researchers were confident that this was the effect of a natural but transient phenomenon - clouds. 'If you wanted to see these clouds from the surface of Mars, you would probably have to wait until after sunset,' said Franck Montmessin, a SPICAM scientist with Aeronomics Department of the French National Centre for Scientific Research (CNRS), who collaborated with researchers in Russia and Belgium to publish the results in ICARUS, the International Journal of Solar System Studies. The clouds appear to be similar to the mesospheric clouds found on Earth. Because the clouds are so high, they can be seen thanks to reflected light, often appear to shine brightly at twilight, and are often referred to as 'noctilucent'. On Earth, these clouds also occur around 80 km up, but because of the differences in atmosphere and temperature, the clouds themselves must be very different. On Mars, the temperature at 80-100 km would be around -193°C, meaning that the clouds - far too cold to be formed from water - will be formed from carbon dioxide. 'We observe the clouds in super-cold conditions where the main atmospheric component CO2 (carbon dioxide), cools below its condensation point. From that we infer that they are made of carbon dioxide,' says Dr Montmessin. However, the clouds may provide insight into phenomena on Earth. Mars has frequently been cited as a very extreme example of what could happen under extreme global warming. On Earth, some experts have suggested that mesospheric clouds are forming more often and at lower altitudes than before. While this makes for beautiful sunsets, they could be the work of atmospheric particles or global warming. On Mars, the clouds seem to form thanks to a thin layer of dust grains, around 60 km up. These tiny grains are on the nanoparticle-scale and could be debris from meteors plunging through the Martian atmosphere or the result of very high winds on the harsh surface below. The team believes that these particles could be responsible for the clouds, allowing CO2 to condense on the particles and then evaporate and rise higher still, generating the clouds. This could be a model for something similar occurring on Earth. The research also suggests that the Martian atmosphere is denser than previously supposed, and this could influence the design of future missions to Mars.
Countries
Belgium, France, Russia